Xantia V6 broken exhaust (update: and rough low rpm running)

[Mandrake]

Away from the garage last night I was careful not to let the ignition sit in position II for too long before starting - like before, firing up the engine before the warning lights go out. The outbound journey earlier was the same. On both journeys the car was healthy sounding, ran well, and mpg was good (70ish mph on the A1 was getting 30-45mpg depending on gradient). However, without thinking, I started the engine before heading back AFTER the ignition had been in position II for about 15 minutes (the engine was still warm at this point, but not so much it was showing on the temp gauge). Power-loss wasn't too bad, but the drone was deafening again and fuel consumption was horrendous. My girlfriend even commented when we got to the country roads that "she sounds very noisy again". I pulled into a lay-bay, knocked-off the ignition, took the key out and then re-started quickly. Suddenly we're back to quiet, smooth and economical mode despite a warm start.

Something is definitely happening when the key is in position II for too long. Whether it's like I said before and the ECU is having the time to re-load incorrect parameters - I've said before that I think the ECU only applies new parameters at start-up, not mid-journey, so maybe it's adjusting for the weak spark/bad ignition it detected at the oxygen sensor on the previous journey (as yours may do with the incorrect sensor) and applying those settings. Firing-up immediately might by-pass these settings and so the ECU either works with preset defaults or simply does things on-the-fly.

Very interesting. However I have to ask - why did you have the key on in position two with the engine stopped for 15 minutes ?? Not a normal occurrence I would say, and all bets are off then. I can tell you what it isn't, and suggest a couple of things it might be.

If key off then an immediate restart cured it, it won't be anything to do with the oxygen sensor, fuel trim (learnt from the oxygen sensor) or timing advance (learnt from the knock sensor) as those are constantly learning and adapting as you drive the car, they don't require a key off then on to take them into account. Also when you turn off the engine both tables are kept in battery backed memory and used immediately when you start the engine again (unless you take the battery off for 10 minutes or perhaps do your "ICV reset" procedure) so the fact that you cure the problem by switching it off and on tells me its not fuel trim or timing related.

I'll tell you what IS recalibrated every time you turn on the key to start the car though - the TPS idle position, and the MAP sensor barometric calibration...

For the TPS, every time you turn the key on to position two, if the TPS voltage is less than a certain threshold (I'm not sure exactly what the threshold is, but its around 0.9 - 1.0 volts from my experimentation) the ECU then calibrates this as a fully closed throttle position, until otherwise contradicted by a lower voltage reading. Typical closed throttle voltages are around 0.6 - 0.7 volts. If the voltage is above this 0.9-1.0 volt threshold when the key is turned on calibration does NOT take place as the computer assumes (reasonably) that you are pressing the throttle. Only if it is near closed will it assume that it is closed and calibrate that as the zero degree position.

This means that if you hold the throttle open slightly when the key is turned on, this is calibrated as closed throttle. I've proven this conclusively with the Lexia, where you can get a real time reading of both raw TPS output voltage AND throttle opening percentage which is derived from the voltage, taking into account idle and full throttle calibration.

For example my normal closed throttle voltage is about 0.65 volts, if I hold the throttle down slightly so that the voltage is 0.8 volts it will read about 5 degrees of throttle opening, however if I keep it held at that position and turn the key off and on then now it will show 0.8 volts as zero degrees of throttle opening even though the throttle is held open slightly. If I increase the throttle opening the opening in degrees will increase but remains about 5 degrees in error. If I reduce the throttle opening to 0.8 volts it drops to zero degrees again. If I let the throttle fully close so it drops to 0.65 volts it still reads zero degrees, but if I then open it to 0.8 volts again it will now read 5 degrees.

This proves conclusively that the calibration can change (in one direction only) while the engine is running - if it encounters a voltage that is lower than the previously seen minimum since last turn on, a recalibration occurs on the fly and the new minimum voltage becomes the new zero degree throttle opening point. Now image what happens if the connection to the TPS goes open circuit momentarily while driving allowing it to drop right down to zero volts, even for a fraction of a second...correct calibration is lost and can only be restored by turning the key off and on with the throttle not depressed, as it will not change calibration in the other direction while driving. (It will only "expand" the voltage range while driving, not contract it)

Calibration of full throttle works in a similar way - it will make an initial assumption of the full throttle voltage to begin with of around 4.3-4.4 volts (?) but if it sees a higher voltage than this during driving the new maximum becomes the new full throttle position, so full throttle is recalibrated. I THINK you can manually calibrate full throttle with the key on and engine off using the 10 seconds key on, 10 second full throttle, 10 second closed throttle technique, but I have not verified this.

Now imagine what happens if the ground wire to the TPS looses contact momentarily while driving - calibration of full throttle is mucked up as the ECU would temporarily see a full 5 volts which is outside the normal range of 0.6v to 4.5v. Key off and on should fix this if the fault was only momentary. Of course momentary loss of contact between the wiper and the carbon track when moved quickly (dead spots) is a common way that a TPS or any potentiometer can fail when it wears out, so its easy to see how a failing TPS could cause these kind of symptoms where calibration of the TPS is randomly lost until the next key on calibration.

The MAP sensor is also calibrated for local barometric pressure during key on but before cranking, on the basis that with the engine not spinning there is no vacuum, and the MAP sensor will read accurate barometric pressure even with the throttle closed. (The ICV is still half open anyway, when the key is on waiting to start) This barometric pressure reading is memorised and used to calibrate the MAP readings - since the MAP sensor is a manifold absolute pressure sensor and not a relative vacuum gauge, the same amount of relative vacuum at a different altitude would give a different MAP pressure reading.

So to work out how much vacuum there is, ambient barometric pressure needs to be known so that current measured pressure can be subtracted from it to calculate vacuum and thus engine load. Great, so how does it account for changes in barometric pressure if you climb or descend a mountain without turning the engine off and on ? The answer is that it simply waits for you to fully depress the throttle while you're driving, the MAP reading when the throttle is fully depressed is assumed to be ambient barometric pressure since there is no throttle plate restriction - even though the engine is pumping there will be no vacuum. This reading now becomes the newly memorised barometric pressure used in calculations until the next time the throttle is fully depressed. (or the key switched off and on with the engine not turning over)

Seems a bit mickey mouse, but that's what a lot / most petrol engine cars do! I don't know how close to full throttle you have to get for a calibration to be performed - whether it has to be flat to the floor, or whether something like 70% is sufficient - at low rpm anything over about 50% throttle usually pegs the MAP reading at maximum (ambient) so I'd say it doesn't require completely flooring the throttle.

A few cars do have a separate barometric pressure sensor (sometimes in the same plastic package) that constantly measures the barometric pressure directly by sampling it in the engine bay instead of the manifold - if some go to the trouble of adding a second sensor purely to read ambient pressure an accurate determination of barometric pressure must be reasonably important in the calculations...

Are you starting to see a dependence between the TPS and the MAP here ? While driving, the TPS signal is also used as a trigger to initiate a barometric pressure re-calibration, what if instead of only occurring at full throttle as it should, the MAP recalibration occasionally occurs at a condition of significant vacuum, due to a fault in the TPS or TPS wiring ? This would throw things out dramatically. Fuelling is based largely on MAP reading for low throttle openings and TPS for large throttle openings. If it thought the barometric pressure was lower than it really was, the MAP derived load figure would be way too high, which may cause the ECU to over fuel when in open loop mode...so much so that the engine could be running massively rich under some conditions.

Meanwhile if the TPS calibration is screwed up the fuelling under wide throttle may also be wrong. (The oxygen sensor isn't used when the throttle is moved quickly, nor above an engine load of around 30-40%, and again its the MAP sensor and TPS that determine the engine load) Turn the key off and on and the TPS and MAP are recalibrated from fresh and the problem goes away.

Here's the thing - I've observed the same symptoms as you many times. Performance on a long drive would get lethargic and the exhaust would start to drone and boom but there was no power. Stopping, turning the key off, waiting a few seconds then starting it like you did usually fixed it. I'd love to tell you what fixed it, but I don't know for sure - it hasn't had this symptom for over 6 months, and a lot has changed since then.

I'm reasonably sure its related to MAP and TPS signals and both of mine have been replaced, but then so to have both of yours ? I've also checked and cleaned the contacts on the ECU connector and sensor connectors.

OR something is happening with the fuel pressure during this time - I say this because my drone was a permanent feature before I cleaned up the fuel pump terminals. This would suggest either the pump is nodding off to sleep, pressure is leaking off somewhere (my fuel drop when it's like this resembles a leak), or there's a vacuum issue at startup which is affecting the pressure regulator and continues to affect the pressure during the journey (maybe some vapour-lock somewhere). The only argument against this problem being caused by a drop in fuel pressure is that the power delivery doesn't drop too much (when I had dirty fuel pump terminals my power was very low). Maybe having the drone with low fuel pressure was a sign of that AND bad sparks.

I need to sort my other three sparks and see what changes, don't I?

I think the loud drone ultimately just comes from misfiring cylinders, eg cylinders that are dead weight and just pumping gases through - whether ignition misfire, lean misfire or even a rich misfire if enough cylinders are misfiring you get a drone/boom when opening the throttle. So I'm not sure that the drone helps to tell us anything other than the engine is misfiring.

[lexi]

One area I wouldn't use it though is on the seals in a DOT 4 brake system, which are not compatible with mineral oils therefore won't be compatible with mineral lithium grease.

Those are the seals and boots I am thinking of specifically. Red rubber grease in there.

[stevieb]

Very interesting. However I have to ask - why did you have the key on in position two with the engine stopped for 15 minutes ?? Not a normal occurrence I would say, and all bets are off then. I can tell you what it isn't, and suggest a couple of things it might be.

Hehehe, nothing sinister. It was simply the time it took a polystyrene cup of tea to cool from nuclear-reactor-core-temperature to drinkable. The significance of the 15 minutes seems vague in my post, but it was the fact that the behaviour was exactly the same with just leaving the key in position II until the lights go out that I found interesting. I'd been wondering if an instant start may have been benefitting from the first surge from the fuel pump, but pausing that couple of seconds might cause a drop in fuel pressure due to an open injector or the regulator leaking back to the tank - and wondered afterwards if the 15 minutes had exaggerated the problem or merely repeated it. It seems too coincidental that the fuel pump connector problem gave the drone at deafening volumes, and so did this...

As you say though, all bets are off now because I've fitted the rear three plugs...

If key off then an immediate restart cured it, it won't be anything to do with the oxygen sensor, fuel trim (learnt from the oxygen sensor) or timing advance (learnt from the knock sensor) as those are constantly learning and adapting as you drive the car, they don't require a key off then on to take them into account. Also when you turn off the engine both tables are kept in battery backed memory and used immediately when you start the engine again (unless you take the battery off for 10 minutes or perhaps do your "ICV reset" procedure) so the fact that you cure the problem by switching it off and on tells me its not fuel trim or timing related.

I'll tell you what IS recalibrated every time you turn on the key to start the car though - the TPS idle position, and the MAP sensor barometric calibration...

For the TPS, every time you turn the key on to position two, if the TPS voltage is less than a certain threshold (I'm not sure exactly what the threshold is, but its around 0.9 - 1.0 volts from my experimentation) the ECU then calibrates this as a fully closed throttle position, until otherwise contradicted by a lower voltage reading. Typical closed throttle voltages are around 0.6 - 0.7 volts. If the voltage is above this 0.9-1.0 volt threshold when the key is turned on calibration does NOT take place as the computer assumes (reasonably) that you are pressing the throttle. Only if it is near closed will it assume that it is closed and calibrate that as the zero degree position.

This means that if you hold the throttle open slightly when the key is turned on, this is calibrated as closed throttle. I've proven this conclusively with the Lexia, where you can get a real time reading of both raw TPS output voltage AND throttle opening percentage which is derived from the voltage, taking into account idle and full throttle calibration.

For example my normal closed throttle voltage is about 0.65 volts, if I hold the throttle down slightly so that the voltage is 0.8 volts it will read about 5 degrees of throttle opening, however if I keep it held at that position and turn the key off and on then now it will show 0.8 volts as zero degrees of throttle opening even though the throttle is held open slightly. If I increase the throttle opening the opening in degrees will increase but remains about 5 degrees in error. If I reduce the throttle opening to 0.8 volts it drops to zero degrees again. If I let the throttle fully close so it drops to 0.65 volts it still reads zero degrees, but if I then open it to 0.8 volts again it will now read 5 degrees.

This proves conclusively that the calibration can change (in one direction only) while the engine is running - if it encounters a voltage that is lower than the previously seen minimum since last turn on, a recalibration occurs on the fly and the new minimum voltage becomes the new zero degree throttle opening point. Now image what happens if the connection to the TPS goes open circuit momentarily while driving allowing it to drop right down to zero volts, even for a fraction of a second...correct calibration is lost and can only be restored by turning the key off and on with the throttle not depressed, as it will not change calibration in the other direction while driving. (It will only "expand" the voltage range while driving, not contract it)

Calibration of full throttle works in a similar way - it will make an initial assumption of the full throttle voltage to begin with of around 4.3-4.4 volts (?) but if it sees a higher voltage than this during driving the new maximum becomes the new full throttle position, so full throttle is recalibrated. I THINK you can manually calibrate full throttle with the key on and engine off using the 10 seconds key on, 10 second full throttle, 10 second closed throttle technique, but I have not verified this.

Now imagine what happens if the ground wire to the TPS looses contact momentarily while driving - calibration of full throttle is mucked up as the ECU would temporarily see a full 5 volts which is outside the normal range of 0.6v to 4.5v. Key off and on should fix this if the fault was only momentary. Of course momentary loss of contact between the wiper and the carbon track when moved quickly (dead spots) is a common way that a TPS or any potentiometer can fail when it wears out, so its easy to see how a failing TPS could cause these kind of symptoms where calibration of the TPS is randomly lost until the next key on calibration.

The MAP sensor is also calibrated for local barometric pressure during key on but before cranking, on the basis that with the engine not spinning there is no vacuum, and the MAP sensor will read accurate barometric pressure even with the throttle closed. (The ICV is still half open anyway, when the key is on waiting to start) This barometric pressure reading is memorised and used to calibrate the MAP readings - since the MAP sensor is a manifold absolute pressure sensor and not a relative vacuum gauge, the same amount of relative vacuum at a different altitude would give a different MAP pressure reading.

So to work out how much vacuum there is, ambient barometric pressure needs to be known so that current measured pressure can be subtracted from it to calculate vacuum and thus engine load. Great, so how does it account for changes in barometric pressure if you climb or descend a mountain without turning the engine off and on ? The answer is that it simply waits for you to fully depress the throttle while you're driving, the MAP reading when the throttle is fully depressed is assumed to be ambient barometric pressure since there is no throttle plate restriction - even though the engine is pumping there will be no vacuum. This reading now becomes the newly memorised barometric pressure used in calculations until the next time the throttle is fully depressed. (or the key switched off and on with the engine not turning over)

Seems a bit mickey mouse, but that's what a lot / most petrol engine cars do! I don't know how close to full throttle you have to get for a calibration to be performed - whether it has to be flat to the floor, or whether something like 70% is sufficient - at low rpm anything over about 50% throttle usually pegs the MAP reading at maximum (ambient) so I'd say it doesn't require completely flooring the throttle.

A few cars do have a separate barometric pressure sensor (sometimes in the same plastic package) that constantly measures the barometric pressure directly by sampling it in the engine bay instead of the manifold - if some go to the trouble of adding a second sensor purely to read ambient pressure an accurate determination of barometric pressure must be reasonably important in the calculations...

Are you starting to see a dependence between the TPS and the MAP here ? While driving, the TPS signal is also used as a trigger to initiate a barometric pressure re-calibration, what if instead of only occurring at full throttle as it should, the MAP recalibration occasionally occurs at a condition of significant vacuum, due to a fault in the TPS or TPS wiring ? This would throw things out dramatically. Fuelling is based largely on MAP reading for low throttle openings and TPS for large throttle openings. If it thought the barometric pressure was lower than it really was, the MAP derived load figure would be way too high, which may cause the ECU to over fuel when in open loop mode...so much so that the engine could be running massively rich under some conditions.

Meanwhile if the TPS calibration is screwed up the fuelling under wide throttle may also be wrong. (The oxygen sensor isn't used when the throttle is moved quickly, nor above an engine load of around 30-40%, and again its the MAP sensor and TPS that determine the engine load) Turn the key off and on and the TPS and MAP are recalibrated from fresh and the problem goes away.

Here's the thing - I've observed the same symptoms as you many times. Performance on a long drive would get lethargic and the exhaust would start to drone and boom but there was no power. Stopping, turning the key off, waiting a few seconds then starting it like you did usually fixed it. I'd love to tell you what fixed it, but I don't know for sure - it hasn't had this symptom for over 6 months, and a lot has changed since then.

I'm reasonably sure its related to MAP and TPS signals and both of mine have been replaced, but then so to have both of yours ? I've also checked and cleaned the contacts on the ECU connector and sensor connectors.

I think the loud drone ultimately just comes from misfiring cylinders, eg cylinders that are dead weight and just pumping gases through - whether ignition misfire, lean misfire or even a rich misfire if enough cylinders are misfiring you get a drone/boom when opening the throttle. So I'm not sure that the drone helps to tell us anything other than the engine is misfiring.

Further updates on mine that might add to the mix.

The first one fits in with the TPS voltage idea (I now see why there are two methods for calibrating the thing). As well as the exhaust drone coming with the fuel connector issue, I also remember it being cured in the past with a throttle body cleanup - so we're back to the TPS again. I always presumed that the gunk in the throttle body was causing the butterfly to rest in one of those "higher voltage" areas and so when it returned to its natural rest position the ECU was confused by the negative figure/position it was seeing. But from what you're saying, the ECU can re-calibrate its zero-point in use. Hmmm, so now I'm not sure why the throttle body clean should have such an effect (and it's a well-known cure on the Coupé Club so it's not just me). Maybe it really is nothing more than the stickiness causing that momentary delay in the butterfly allowing air to pass. It still doesn't explain why cleaning the throttle body cured the deafening drone though... My head's hurting now (too many late nights and early mornings )

Anyway, with new plugs installed the other day and nothing else changed, I decided to try both coilpacks again. The cracked one was a tiny bit louder at tickover, nothing significant, but louder. Blipping the throttle with this one gave a momentary hesitation, but again, nothing major. Then I tried the better coilpack. Smooth, quiet, sounding good. The exhaust was louder than recent good days, but it was the V6 burble, not the racket it had become and definitely quieter than the cracked coilpack. Then I blipped the throttle, this time sat in the car. And the central display dimmed momentarily - like you get when you spin the starter over... There was a split second hesitation - barely noticeable - but the dimming of the display caught my eye. I've never noticed this before, even when the car has been running with a battery past its best. It did it again and again. Is it that mine is struggling to get the volts through to get an accurate TPS reading? If, as you say, it's based on volts, and not on resistance, then a shortfall in the feed will create havoc. My battery isn't very old, but I'm starting to wonder... The other question would be where does the coilpack feed originate? If it's a direct path straight from the ECU, then I think I seriously need to get the ECU connectors looked at - it's one job I haven't done because they've never needed to be disturbed - maybe they're as bad as the fuel pump...

Another thing is I've had two instances of starts that have taken a couple of seconds to fire - as if there's either no sparks or no fuel. One was a cold morning start after being sat for over 12 hours (with three new plugs in), the other was a warm(ish) start after being sat for around two hours (with all six plugs in). This rules out the CTS, and if you're right that the TPS and MAP sensor re-calibrate at startup then it rules those out too. But then I'm back to that dimming of the centre display - if low volts caused a zero volt-reading back to the ECU, would it refuse to open the injectors or supply a spark but allow the engine to turn over? Like an immobilised state (that IS my other possibility - that the alarm chip/sensor is getting tired). Then when the volts trickled through the TPS the ECU accepted that a startup was being attempted?

On a positive note, outside of this initial weirdness the car has been running well. Since the new plugs have gone in I don't have that difference between instant start and delayed start - I've tried both and they're both identical now. The extreme version of the drone is gone (although there's still a peak in noise at 3,000rpm that then drops off very quickly), but that's the price for the exhaust I've got. At tickover it's barely audible (I can hear my squeaky clutch pedal again ) The only thing so far is that the fuel consumption hasn't been great, but I put that down to a lot of shorter journeys yesterday and today - a trip on the 50mph M1 tomorrow morning might prove interesting.

[Mandrake]

Hehehe, nothing sinister. It was simply the time it took a polystyrene cup of tea to cool from nuclear-reactor-core-temperature to drinkable. The significance of the 15 minutes seems vague in my post, but it was the fact that the behaviour was exactly the same with just leaving the key in position II until the lights go out that I found interesting. I'd been wondering if an instant start may have been benefitting from the first surge from the fuel pump, but pausing that couple of seconds might cause a drop in fuel pressure due to an open injector or the regulator leaking back to the tank - and wondered afterwards if the 15 minutes had exaggerated the problem or merely repeated it. It seems too coincidental that the fuel pump connector problem gave the drone at deafening volumes, and so did this...

If the pressure is leaking away from the rail quickly when the pump is not running then it could certainly have an effect on starting. The pump only energises for about a second when you turn to position two, so if you turned it to two then waited a few seconds before turning to start it might not catch quite as quickly. However I can't see how waiting to engage start or not would have any effect on the ongoing running - once you turn to start and the engine is turning over the fuel pump is on constantly.

By the way I don't know if yours does it - but after mine has been running and has been switched off every few minutes the fuel pump comes back on for a second to prime the fuel rail, I'm not sure how long this goes on for - maybe 15 minutes or so. Something to be aware of when disconnecting the fuel rail! (always remove the fuel pump fuse)

Further updates on mine that might add to the mix.

The first one fits in with the TPS voltage idea (I now see why there are two methods for calibrating the thing). As well as the exhaust drone coming with the fuel connector issue, I also remember it being cured in the past with a throttle body cleanup - so we're back to the TPS again. I always presumed that the gunk in the throttle body was causing the butterfly to rest in one of those "higher voltage" areas and so when it returned to its natural rest position the ECU was confused by the negative figure/position it was seeing. But from what you're saying, the ECU can re-calibrate its zero-point in use. Hmmm, so now I'm not sure why the throttle body clean should have such an effect (and it's a well-known cure on the Coupé Club so it's not just me). Maybe it really is nothing more than the stickiness causing that momentary delay in the butterfly allowing air to pass.

Cleaning the throttle body is not just a placebo - the gunk doesn't prevent the throttle plate mechanically closing fully as far as I'm aware (it's only oily carbon and the spring is pretty strong!) however it seals around the edge of the throttle plate like a gasket.

From what I've read normal throttle plate behaviour is that there is a small calibrated leak around the edge of the throttle plate that provides some of the air needed to idle (with the ICV making up the difference) and that a clean throttle plate will cause the air flow to smoothly start to increase even with the tiniest angular movement of the plate - no dead zone.

On a dirty throttle plate the oily carbon residue acts as a gasket around the edge completely blocking the air flow when the throttle plate is closed. (The ICV compensates by opening a bit more than normal) The problem is that with that residue there as you start to open the throttle plate the residue continues to seal the edge of the plate until it tilts at a sufficient angle to clear the gunk - so you end up with a "dead zone" where the first few (5 ?) degrees of throttle movement doesn't actually cause any increase in air flow even though the TPS is turning and telling the ECU you're opening the throttle.

Therefore the ECU thinks you've left the idle state (throttle partially open) but the air flow has not increased, or not increased as much as expected. Now that you're no longer in idle state the ECU stops trying to regulate the idle with the ICV and you potentially get a dip in revs if the air through the throttle plate is lower than it should be. With the throttle off idle only if the revs drop to a near stall will the ICV intervene and open to prevent the stall. (Hence the near stall then surge)

It still doesn't explain why cleaning the throttle body cured the deafening drone though... My head's hurting now (too many late nights and early mornings )

No idea on that one, sorry!

Anyway, with new plugs installed the other day and nothing else changed, I decided to try both coilpacks again. The cracked one was a tiny bit louder at tickover, nothing significant, but louder. Blipping the throttle with this one gave a momentary hesitation, but again, nothing major. Then I tried the better coilpack. Smooth, quiet, sounding good. The exhaust was louder than recent good days, but it was the V6 burble, not the racket it had become and definitely quieter than the cracked coilpack. Then I blipped the throttle, this time sat in the car. And the central display dimmed momentarily - like you get when you spin the starter over... There was a split second hesitation - barely noticeable - but the dimming of the display caught my eye. I've never noticed this before, even when the car has been running with a battery past its best. It did it again and again. Is it that mine is struggling to get the volts through to get an accurate TPS reading? If, as you say, it's based on volts, and not on resistance, then a shortfall in the feed will create havoc. My battery isn't very old, but I'm starting to wonder...

The display dimming when you blipped the throttle is simply the engine rpm dropping below normal idle speed. The output voltage from the alternator drops rapidly below idle speed. When you say blipped throttle, do you mean you were flooring it at idle (I'd call that a snap throttle test) or were you just lightly tapping it but not really depressing it ? The lights on my dashboard dim if I do the light throttle tap and the engine tries to stall - I posted a video of that earlier.

The other question would be where does the coilpack feed originate? If it's a direct path straight from the ECU, then I think I seriously need to get the ECU connectors looked at - it's one job I haven't done because they've never needed to be disturbed - maybe they're as bad as the fuel pump...

The positive supply for the coil pack (shared by all three coils) comes from one of the "double injection relays" - which are the two relays inside the plastic ECU container with fly leads and a connector with a sliding section. At least on the Xantia! Not sure where they will be on a 406 but I'd look in the box with the ECU first. The ground return of each coil goes back directly to the ECU connector as the ECU has the ignition drivers built in and grounds the coil to charge it.

Another thing is I've had two instances of starts that have taken a couple of seconds to fire - as if there's either no sparks or no fuel. One was a cold morning start after being sat for over 12 hours (with three new plugs in), the other was a warm(ish) start after being sat for around two hours (with all six plugs in). This rules out the CTS, and if you're right that the TPS and MAP sensor re-calibrate at startup then it rules those out too. But then I'm back to that dimming of the centre display - if low volts caused a zero volt-reading back to the ECU, would it refuse to open the injectors or supply a spark but allow the engine to turn over? Like an immobilised state (that IS my other possibility - that the alarm chip/sensor is getting tired). Then when the volts trickled through the TPS the ECU accepted that a startup was being attempted?

As I said above, the dimming of the centre display is a natural result if the engine rpm dips below normal 650 rpm, I wouldn't worry about it except in so much as finding out why the rpm is dipping too low. The TPS runs off a regulated 5 volt rail - low battery voltage won't cause the 5 volt reference to drop so don't worry about that.

On a positive note, outside of this initial weirdness the car has been running well. Since the new plugs have gone in I don't have that difference between instant start and delayed start - I've tried both and they're both identical now. The extreme version of the drone is gone (although there's still a peak in noise at 3,000rpm that then drops off very quickly), but that's the price for the exhaust I've got. At tickover it's barely audible (I can hear my squeaky clutch pedal again ) The only thing so far is that the fuel consumption hasn't been great, but I put that down to a lot of shorter journeys yesterday and today - a trip on the 50mph M1 tomorrow morning might prove interesting.

Sounds like overall you've made good progress, especially if performance is always good. MPG is always going to vary with conditions, temperature etc so is a less reliable indicator of how well the car is running than the throttle response and power. Likewise exhaust note varying slightly I wouldn't worry about too much.

Mine is running well too aside from some momentary hesitation here and there - yesterday was very wet, heavy rain, a lot of water on the road and yet it was going like a little rocket. It's too early to be certain yet but I think there is a definite and quite significant improvement in engine performance in WET, damp conditions since I greased the spark plug lead boots with lithium grease. It's running better in the wet now than it was a week ago before I swapped the coil then swapped it back.

The rubber boots on the spark plug leads that go onto the top of the coils really don't fit very well now I look closer - they should (must!) be a snug air-tight fit and they're not, they're quite a sloppy fit. I'm starting to wonder if some of the "runs better for a while then gets worse" I was seeing every time I swapped a coil pack was in fact these poorly fitting (but new!!) spark plug lead boots ? They'll be making electrical connection ok (there is a spring cir-clip to see to that) but if the boot is not air tight then moisture will find its way in and you will get high voltage "leakage" out through the gap between the boot and the plastic elbow, leakage that will get worse in damp conditions. There is enough movement of the boot that vibration could move it around slightly opening up a gap to the outside air.

Regarding the stumble at idle I'm going to have another look at the throttle plate to make sure its clean and also check the idle stop (the tiny screw under a plastic cap on the left of the throttle body) - yes I admit that I fiddled with the idle stop recently. The stumble was already there before that, however due to the ICV being too closed at idle I tried closing the throttle body slightly more with the idle screw - in hindsight I think this is the cause of the occasional jerking back and forth I see on the overrun with the throttle closed in 1st gear. So I'm going to increase the idle screw setting again and see what happens. I also have a hunch that opening the throttle plate idle screw slightly might help with the engine rev dip then surge that sometimes occurs, by slightly increasing the minimum idle speed that can occur with the ICV closed.

Thinking about vacuum leaks, if my oil cap o-ring is not sealing properly is it possible that extra air could be sucked in there through the crankcase ventilation system ? I'm not sure that I understand exactly how the ventilation system works without causing a massive vacuum leak in the intake manifold (no PCV valve on these engines) - does it just rely on the crank case and rocker covers (including oil cap) all being air tight ?? Is it worth me finding an additional flat o-ring to slip over the one on the oil cap ? The existing one looks very flat and very hard, and when fitting it it doesn't feel like its sealing well.

In other news my injectors have arrived (at the post office unfortunately as nobody was in) so I'm going to collect those tomorrow and start striping/cleaning/testing those this weekend although I doubt I'd be able to swap them over until the following weekend at the earliest!

Onward and upwards.

[stevieb]

If the pressure is leaking away from the rail quickly when the pump is not running then it could certainly have an effect on starting. The pump only energises for about a second when you turn to position two, so if you turned it to two then waited a few seconds before turning to start it might not catch quite as quickly. However I can't see how waiting to engage start or not would have any effect on the ongoing running - once you turn to start and the engine is turning over the fuel pump is on constantly.

By the way I don't know if yours does it - but after mine has been running and has been switched off every few minutes the fuel pump comes back on for a second to prime the fuel rail, I'm not sure how long this goes on for - maybe 15 minutes or so. Something to be aware of when disconnecting the fuel rail! (always remove the fuel pump fuse)

I always thought the pump ran a lot longer with the key in position II. Mine certainly did after I'd cleaned up the terminals and tested it before I'd re-fitted the back seat. The thing that's conspicuous now is the lack of pump noise when I turn on the ignition - I could hear it before. I'm not sure when this changed, but maybe it's just quieter now it's getting the full 12 volts, or maybe it is failing now more demand is being placed on it. I've come across this before with electric motors when they get tired - they run fine on a lower voltage, but try to run them at their rated voltage and they're not happy, demanding more amps than they're supposed to work with. This causes hot wiring and connectors, which might be why mine had begun corroding...

I'm still tempted to check my fuel pressure, but it can wait for now - read on...

Cleaning the throttle body is not just a placebo - the gunk doesn't prevent the throttle plate mechanically closing fully as far as I'm aware (it's only oily carbon and the spring is pretty strong!) however it seals around the edge of the throttle plate like a gasket.

From what I've read normal throttle plate behaviour is that there is a small calibrated leak around the edge of the throttle plate that provides some of the air needed to idle (with the ICV making up the difference) and that a clean throttle plate will cause the air flow to smoothly start to increase even with the tiniest angular movement of the plate - no dead zone.

On a dirty throttle plate the oily carbon residue acts as a gasket around the edge completely blocking the air flow when the throttle plate is closed. (The ICV compensates by opening a bit more than normal) The problem is that with that residue there as you start to open the throttle plate the residue continues to seal the edge of the plate until it tilts at a sufficient angle to clear the gunk - so you end up with a "dead zone" where the first few (5 ?) degrees of throttle movement doesn't actually cause any increase in air flow even though the TPS is turning and telling the ECU you're opening the throttle.

Therefore the ECU thinks you've left the idle state (throttle partially open) but the air flow has not increased, or not increased as much as expected. Now that you're no longer in idle state the ECU stops trying to regulate the idle with the ICV and you potentially get a dip in revs if the air through the throttle plate is lower than it should be. With the throttle off idle only if the revs drop to a near stall will the ICV intervene and open to prevent the stall. (Hence the near stall then surge)

That makes sense. I just struggled to imagine the gunk being elastic enough to create that air-tight film. I know that snapping the throttle (engine off) when the gunk is in there results in a dull thud as the butterfly snaps shut - it's a very definite metallic sound once it's cleaned - so I'd always assumed the TPS was getting an incorrect zero-point reading. It seems I need to re-think that idea.

The display dimming when you blipped the throttle is simply the engine rpm dropping below normal idle speed. The output voltage from the alternator drops rapidly below idle speed. When you say blipped throttle, do you mean you were flooring it at idle (I'd call that a snap throttle test) or were you just lightly tapping it but not really depressing it ? The lights on my dashboard dim if I do the light throttle tap and the engine tries to stall - I posted a video of that earlier.

It was just a throttle tap - I was trying to see if the engine would hesitate with the new plugs installed. The concerning thing is that I've never seen this before, and I've certainly tried throttle blipping often enough in the last seven years. As it is, I cleaned up the battery terminals yesterday before I headed out - I'd decided another ECU reset couldn't hurt either. The battery terminals were dulled, but not grotty. I took some emery cloth to the posts, the terminals, and my copper-pipe size-changers until everything was shiny then re-assembled with copper grease. There was no change in the startup time, (taking a little longer than normal, presumably thanks to the ECU reset), but the dimming central display is massively reduced so I can only assume there was a power issue there somewhere. I guess if other connectors are tarnished and beginning to corrode then the losses will begin to mount up - and at least ensuring full voltage from the source should improve things. Time to go through the other potential culprits now methinks...

The positive supply for the coil pack (shared by all three coils) comes from one of the "double injection relays" - which are the two relays inside the plastic ECU container with fly leads and a connector with a sliding section. At least on the Xantia! Not sure where they will be on a 406 but I'd look in the box with the ECU first. The ground return of each coil goes back directly to the ECU connector as the ECU has the ignition drivers built in and grounds the coil to charge it.

Thanks for that Simon - I'll go through these as soon as I get chance

As I said above, the dimming of the centre display is a natural result if the engine rpm dips below normal 650 rpm, I wouldn't worry about it except in so much as finding out why the rpm is dipping too low. The TPS runs off a regulated 5 volt rail - low battery voltage won't cause the 5 volt reference to drop so don't worry about that.

That's good to hear. I'd wondered why the ECU took a voltage reference rather than simply measuring the varying resistance, but I guess there was a logic there somewhere.

Sounds like overall you've made good progress, especially if performance is always good. MPG is always going to vary with conditions, temperature etc so is a less reliable indicator of how well the car is running than the throttle response and power. Likewise exhaust note varying slightly I wouldn't worry about too much.

Mine is running well too aside from some momentary hesitation here and there - yesterday was very wet, heavy rain, a lot of water on the road and yet it was going like a little rocket. It's too early to be certain yet but I think there is a definite and quite significant improvement in engine performance in WET, damp conditions since I greased the spark plug lead boots with lithium grease. It's running better in the wet now than it was a week ago before I swapped the coil then swapped it back.

The rubber boots on the spark plug leads that go onto the top of the coils really don't fit very well now I look closer - they should (must!) be a snug air-tight fit and they're not, they're quite a sloppy fit. I'm starting to wonder if some of the "runs better for a while then gets worse" I was seeing every time I swapped a coil pack was in fact these poorly fitting (but new!!) spark plug lead boots ? They'll be making electrical connection ok (there is a spring cir-clip to see to that) but if the boot is not air tight then moisture will find its way in and you will get high voltage "leakage" out through the gap between the boot and the plastic elbow, leakage that will get worse in damp conditions. There is enough movement of the boot that vibration could move it around slightly opening up a gap to the outside air.

Regarding the stumble at idle I'm going to have another look at the throttle plate to make sure its clean and also check the idle stop (the tiny screw under a plastic cap on the left of the throttle body) - yes I admit that I fiddled with the idle stop recently. The stumble was already there before that, however due to the ICV being too closed at idle I tried closing the throttle body slightly more with the idle screw - in hindsight I think this is the cause of the occasional jerking back and forth I see on the overrun with the throttle closed in 1st gear. So I'm going to increase the idle screw setting again and see what happens. I also have a hunch that opening the throttle plate idle screw slightly might help with the engine rev dip then surge that sometimes occurs, by slightly increasing the minimum idle speed that can occur with the ICV closed.

Thinking about vacuum leaks, if my oil cap o-ring is not sealing properly is it possible that extra air could be sucked in there through the crankcase ventilation system ? I'm not sure that I understand exactly how the ventilation system works without causing a massive vacuum leak in the intake manifold (no PCV valve on these engines) - does it just rely on the crank case and rocker covers (including oil cap) all being air tight ?? Is it worth me finding an additional flat o-ring to slip over the one on the oil cap ? The existing one looks very flat and very hard, and when fitting it it doesn't feel like its sealing well.

In other news my injectors have arrived (at the post office unfortunately as nobody was in) so I'm going to collect those tomorrow and start striping/cleaning/testing those this weekend although I doubt I'd be able to swap them over until the following weekend at the earliest!

Onward and upwards.

Running well indeed. The first 130-odd miles after the ECU reset (a mix of motorway - 50/70mph running - hilly country roads and town driving) saw an average mpg of 35.4. Later in the day I added 20-odd miles of city centre driving and it's dropped to 33.2mpg, but I'm not going to complain too much. The power seemed a lot lower at first, and the drone was back along with a noisier tickover, but as the day went on this diminished more and more to the point I had a lovely quiet tickover and the drone was more of a grumbly burble. I expect a few more days of pootling about might see things improve further.

I haven't had a slow-to-catch startup since the last ECU reset which might be telling, and I've even noticed the engine now catches so quickly the starter solenoid is being caught out. I have re-acquired that slight miss at low rpm/high gear. It's not as violent as it was before (which was on the other coilpack), so I'm not sure what the cause is. For a while now I've found I can hear the drivetrain taking up the slack from standing starts (a worn CV joint I think) and it's getting worse - so maybe what I'm feeling is a little like snatching at the clutch - that momentary hesitation of the engine before the ECU has chance to stop a stall. The weaker coilpack would've exaggerated the problem.

On the point of vacuum leaks I can't imagine the crankcase breathers have any effect. The main breather feeds into the throttle body on the outer, atmospheric, side of the butterfly - so it can't create any down-wind air leaks. If I remember rightly, the only hose feeding the engine side of the throttle butterfly is the fuel tank ventilator hose (I forget the proper term) that has a connector on the bottom of the throttle body. To be honest I don't think there are many places that vacuum leaks can occur - the manifold gasket is the main culprit, followed by the ICV rubber elbow and then the MAP sensor aperture (I was convinced I had a leak past the O-ring on my Intermotor sensor). If you've adjusted the idle stop I'd be looking there first. I've never touched mine, but the throttle butterfly definitely closes fully - I have photos taken into the aperture and there's definitely no visible gaps around the butterfly, and I would've though a tiny gap designed to supplement the ICV would create a lot of noise - the only sucking of air I can hear from mine at tickover comes from the ICV.

Now, the boots on the HT leads... Should I grease mine or leave well alone...? It can't hurt, can it?

[Mandrake]

I always thought the pump ran a lot longer with the key in position II. Mine certainly did after I'd cleaned up the terminals and tested it before I'd re-fitted the back seat. The thing that's conspicuous now is the lack of pump noise when I turn on the ignition - I could hear it before. I'm not sure when this changed, but maybe it's just quieter now it's getting the full 12 volts, or maybe it is failing now more demand is being placed on it. I've come across this before with electric motors when they get tired - they run fine on a lower voltage, but try to run them at their rated voltage and they're not happy, demanding more amps than they're supposed to work with. This causes hot wiring and connectors, which might be why mine had begun corroding...

Have you checked to make sure that the fuel pump isn't generating a vacuum in the tank after a while ? I'm not actually sure whether there is a separate breather for the tank or whether the only form of pressure equalisation is through the charcoal canister line and the canister purge valve ? Does anyone know ?

If the fuel tank was completely air tight due to a blocked breather or the charcoal canister system was blocked somewhere along the way the pump would start to struggle after a while as a vacuum developed, and probably get noisy too. The pressure in the tank would also change with ambient temperature due to expansion/contraction of air in the tank, with greater temperature related variations when the tank is nearing empty and most of the tank is air.

In the past I've sometimes noticed the car instantly running better after freshly filling up with fuel even though the new fuel can't have mixed or made its way to the injectors yet. Could it be that a vacuum lock on the pump was released when I opened the petrol cap ?

If it was mostly blocked but there was still a tiny leak the vacuum might dissipate by itself after the car has been left to sit for a while, but then get worse again as the car is driven and fuel is consumed.

Occasionally I've noticed the pump (at least my original pump) get unusually noisy on very hot days - when the demand comes on it gradually got noisy over a 5-10 second period, then when I slowed down it slowly got quieter again. Could that have been the pump struggling against a vacuum ? Easy way to prove it I guess - a test drive with the fuel cap left off ! (I've never tried it)

It was just a throttle tap - I was trying to see if the engine would hesitate with the new plugs installed. The concerning thing is that I've never seen this before, and I've certainly tried throttle blipping often enough in the last seven years.

Mine does this all the time now and has done for at least several months and I still have no clue as to the cause and it stubbornly resists any attempts to fix it. The annoying thing is it hasn't always done this and I can't remember exactly when it started or whether there was any correlation with anything I did.

On the point of vacuum leaks I can't imagine the crankcase breathers have any effect. The main breather feeds into the throttle body on the outer, atmospheric, side of the butterfly - so it can't create any down-wind air leaks. If I remember rightly, the only hose feeding the engine side of the throttle butterfly is the fuel tank ventilator hose (I forget the proper term) that has a connector on the bottom of the throttle body.

Actually that's not true, unless the 406 has a different throttle body to the Xanita, which seems unlikely. The crank case breather which connects on the lower left of the throttle body goes directly to the manifold vacuum side - try disconnecting it with the engine running and you'll soon find out from the massive suction that occurs with the throttle closed.

Here's a diagram of the air inlet system:

https://dl.dropboxusercontent.com/u/782 ... ircuit.pdf" onclick="window.open(this.href);return false;

The breather hose is item A which is definitely after the throttle plate. Seems like a stupid idea to me but what do I know ? I'm guessing the reason for it is if it was in front of the throttle plate the oil fumes from the breather would rapidly clog up the throttle plate with gunk.

Anyway, because it is actually after the throttle plate any air leaks in the crank case breather system (including cracked breather hoses) would cause a manifold vacuum leak. If those leaks varied intermittently so too would the vacuum leak potentially causing variations in idling.

To be honest I don't think there are many places that vacuum leaks can occur - the manifold gasket is the main culprit, followed by the ICV rubber elbow and then the MAP sensor aperture (I was convinced I had a leak past the O-ring on my Intermotor sensor).

Unless the manifold flanges are warped then it can't be the manifold gasket as the vacuum leak has persisted across multiple manifold gaskets. I suppose it could be one of the lower manifold gaskets but I'm not game to tackle those at the moment as its a lot of extra work to get the lower manifold out, and if I was going to that trouble I'd swap the knock sensor while I was at it! Another possibility is a leaking o-ring on one of the injectors causing a vacuum leak directly above the inlet valve.

The hose from ICV to throttle body I checked when I had it out last time and it seemed ok. I know its not the charcoal canister line as I have that blanked off at the moment at the throttle body!

A smoke machine would most likely find the leak quite easily but I don't have one nor access to borrow one.

If you've adjusted the idle stop I'd be looking there first. I've never touched mine, but the throttle butterfly definitely closes fully - I have photos taken into the aperture and there's definitely no visible gaps around the butterfly, and I would've though a tiny gap designed to supplement the ICV would create a lot of noise - the only sucking of air I can hear from mine at tickover comes from the ICV.

Yes I've put the idle stop back where it should be today. (I think) I turned it clockwise a whole turn at first and that was far too much - idling at 1100 rpm. I backed it off half a turn and it seemed a lot better - I noticed that power take up when driving was a lot smoother rather than an abrupt on throttle / off throttle transition I had before. Unfortunately it was still struggling slightly to get the idle speed down with it lingering a bit too high sometimes, so I backed it off another quarter of a turn (so a quarter of a turn more open than where I started) and it seems to be ok now.

It definitely drives smoother with the screw slightly further open though - but because I have a vacuum leak somewhere the ICV can't get the idle speed low enough in that position. (That's the original reason I closed the idle screw a bit) If I can find and fix my vacuum leak I may be able to open the screw a quarter of a turn again.

Now, the boots on the HT leads... Should I grease mine or leave well alone...? It can't hurt, can it?

No it can't hurt, as long as the grease is clean and a non-conductive type like the plain lithium grease. Don't use grease from a tub that you've put dirty fingers into as it will be contaminated possibly with metallic particles, and don't use copper slip or other specialised mechanical greases that include metallic particles...

Just lift the plug leads off the coil, smear a little bit of grease inside the boot with your pinky and a very thin layer on the outside of the elbow joint on the coil pack. Couldn't be easier. When you put the boot back on it should squelch and hydraulic slightly due to it being an air tight seal so you might need to wriggle it back on.

[Mandrake]

Here's what I've been setting up this afternoon:







I have the second hand fuel rail assembly which I collected from the post office today piped to my original now spare fuel pump (which in hindsight I don't think has anything wrong with it) and the fuel pressure gauge attached to the schrader valve. The injectors are all pointed over a catchment tray.

Because the return flow back to the pump fills the swirl pot and the swirl pot has a one way valve at the bottom preventing flow back into the tank I should just be able to fill the swirl pot with fuel rather than filling the bottom of the plastic dish - the dish is more there to catch spills than be a fuel reservoir.

All I need to do now is get the electrical wiring worked out. Obviously I don't want any sparks over the fuel pump as I don't want to blow myself up! Luckily I have the proper fuel pump connector and about a foot worth of wire still attached to it which came with the second hand fuel pump I got, so I'm going to solder and tape a metre extension to that to bring the connections well away from both bowls.

I'm digging through my assorted bits (mostly packed away in boxes ) trying to find a push button to activate the fuel pump before each pressure drop test, and figure out a good way to connect the injector pulser to the injectors. (I might just have to use croc leads)

Hopefully my 13.8 volt 5 amp bench supply is enough to run the fuel pump, as fuel pumps are around 5-7 amps, otherwise I might have to find a small 12v battery to connect in parallel to bolster it. It will have no trouble supplying the injectors though as they are only about 1 amp.

Then I'll be able to test the fuel pressure regulator, check that the rail holds its pressure over a 10 minutes period (no leaky injectors or regulator) and then do a balance test.

I thought I'd do an initial test before stripping the injectors out and cleaning them, then test again when I'm finished. Fingers crossed!

If I find any significant imbalance between the injectors that I can't cure with basic cleaning I guess I'll need to send them away to get professionally cleaned and tested - no point fitting them if they're not balanced!

By the way am I right in thinking that to remove the retaining plate that holds the injectors the screws can only be accessed from underneath - so that it's impossible to remove an injector in-situ in the car without completely lifting the rails out ??

[stevieb]

Have you checked to make sure that the fuel pump isn't generating a vacuum in the tank after a while ? I'm not actually sure whether there is a separate breather for the tank or whether the only form of pressure equalisation is through the charcoal canister line and the canister purge valve ? Does anyone know ?

If the fuel tank was completely air tight due to a blocked breather or the charcoal canister system was blocked somewhere along the way the pump would start to struggle after a while as a vacuum developed, and probably get noisy too. The pressure in the tank would also change with ambient temperature due to expansion/contraction of air in the tank, with greater temperature related variations when the tank is nearing empty and most of the tank is air.

In the past I've sometimes noticed the car instantly running better after freshly filling up with fuel even though the new fuel can't have mixed or made its way to the injectors yet. Could it be that a vacuum lock on the pump was released when I opened the petrol cap ?

If it was mostly blocked but there was still a tiny leak the vacuum might dissipate by itself after the car has been left to sit for a while, but then get worse again as the car is driven and fuel is consumed.

Occasionally I've noticed the pump (at least my original pump) get unusually noisy on very hot days - when the demand comes on it gradually got noisy over a 5-10 second period, then when I slowed down it slowly got quieter again. Could that have been the pump struggling against a vacuum ? Easy way to prove it I guess - a test drive with the fuel cap left off ! (I've never tried it)

That may well be a good point - I think mine gets worse as the fuel level drops (and it hasn't seen the full mark for quite a while now ), so maybe I need to investigate this further. I'm certain I've read that the fuel system is designed to be air-tight though - no breathing fuel vapour to the atmosphere - and if this is the case then I need to see what's creating the blockage. Either that or use one of my very small drill-bits and put a tiny hole in the filler cap like cars used to have. It wouldn't take much to fill the hole again if need be...

Mine does this all the time now and has done for at least several months and I still have no clue as to the cause and it stubbornly resists any attempts to fix it. The annoying thing is it hasn't always done this and I can't remember exactly when it started or whether there was any correlation with anything I did.

Well I haven't disturbed anything major that could've caused it, and it certainly didn't do it before. The only change has been the new plugs

Actually that's not true, unless the 406 has a different throttle body to the Xantia, which seems unlikely. The crank case breather which connects on the lower left of the throttle body goes directly to the manifold vacuum side - try disconnecting it with the engine running and you'll soon find out from the massive suction that occurs with the throttle closed.

Here's a diagram of the air inlet system:

https://dl.dropboxusercontent.com/u/782 ... ircuit.pdf" onclick="window.open(this.href);return false;

The breather hose is item A which is definitely after the throttle plate. Seems like a stupid idea to me but what do I know ? I'm guessing the reason for it is if it was in front of the throttle plate the oil fumes from the breather would rapidly clog up the throttle plate with gunk.

Anyway, because it is actually after the throttle plate any air leaks in the crank case breather system (including cracked breather hoses) would cause a manifold vacuum leak. If those leaks varied intermittently so too would the vacuum leak potentially causing variations in idling.

I'd forgotten all about that connector. I was thinking about the fatter one on the rubber hose between air box and throttle body, which is the crankcase breather. The one after the butterfly is the one fed from the rocker cover breather hoses, and as you say could be the cause of your vacuum leak. This is the one that causes the inside of the inlet manifold to acquire a film of engine oil, usually in three of the passages, but not the other three. Sorry for any confusion thrown into the mix on that one.

Unless the manifold flanges are warped then it can't be the manifold gasket as the vacuum leak has persisted across multiple manifold gaskets. I suppose it could be one of the lower manifold gaskets but I'm not game to tackle those at the moment as its a lot of extra work to get the lower manifold out, and if I was going to that trouble I'd swap the knock sensor while I was at it! Another possibility is a leaking o-ring on one of the injectors causing a vacuum leak directly above the inlet valve.

The hose from ICV to throttle body I checked when I had it out last time and it seemed ok. I know its not the charcoal canister line as I have that blanked off at the moment at the throttle body!

A smoke machine would most likely find the leak quite easily but I don't have one nor access to borrow one.

Ooh, I don't know about the manifold gasket - if the two metallic surfaces are perfectly machined but the gasket isn't perfectly even then there will still be weak spots. The one I took off last week had areas where it had definitely been crushed, but a few areas where the print was still all shiny and new - where it hadn't been clamped as tightly as I would've liked. When fitting the new one I gave all the contacting surfaces a good film of fresh engine oil to try and swell the gasket - this may be as much to do with my improved running as anything else if there were tiny leaks affecting just one or two cylinders. I know I've read of people with consistent problems getting these gaskets to seal, who have ended up using sump-gasket Loctite to create a better seal and had success - maybe these has warped manifolds, or maybe not, but can you be sure yours are perfectly straight...?

I would imagine you've checked all that, but it's one of those things that's easy to assume is "right", when in fact it might not be.

Yes I've put the idle stop back where it should be today. (I think) I turned it clockwise a whole turn at first and that was far too much - idling at 1100 rpm. I backed it off half a turn and it seemed a lot better - I noticed that power take up when driving was a lot smoother rather than an abrupt on throttle / off throttle transition I had before. Unfortunately it was still struggling slightly to get the idle speed down with it lingering a bit too high sometimes, so I backed it off another quarter of a turn (so a quarter of a turn more open than where I started) and it seems to be ok now.

It definitely drives smoother with the screw slightly further open though - but because I have a vacuum leak somewhere the ICV can't get the idle speed low enough in that position. (That's the original reason I closed the idle screw a bit) If I can find and fix my vacuum leak I may be able to open the screw a quarter of a turn again.

I think this one will finally reach its natural conclusion when the vacuum leak is sorted...

No it can't hurt, as long as the grease is clean and a non-conductive type like the plain lithium grease. Don't use grease from a tub that you've put dirty fingers into as it will be contaminated possibly with metallic particles, and don't use copper slip or other specialised mechanical greases that include metallic particles...

Just lift the plug leads off the coil, smear a little bit of grease inside the boot with your pinky and a very thin layer on the outside of the elbow joint on the coil pack. Couldn't be easier. When you put the boot back on it should squelch and hydraulic slightly due to it being an air tight seal so you might need to wriggle it back on.

This might be a Sunday job, subject to the weather. I need to suss out why the car is squirming first though (a 9 month old wishbone bush is most likely - gonna try some of these American "Moog" ones if it turns out to be that).

[stevieb]

By the way am I right in thinking that to remove the retaining plate that holds the injectors the screws can only be accessed from underneath - so that it's impossible to remove an injector in-situ in the car without completely lifting the rails out ??

Yup. Six Torx bolts - T30 I think (but don't hold me to that - I've had a sleep since I did mine)

[Mandrake]

That may well be a good point - I think mine gets worse as the fuel level drops (and it hasn't seen the full mark for quite a while now ), so maybe I need to investigate this further. I'm certain I've read that the fuel system is designed to be air-tight though - no breathing fuel vapour to the atmosphere - and if this is the case then I need to see what's creating the blockage. Either that or use one of my very small drill-bits and put a tiny hole in the filler cap like cars used to have. It wouldn't take much to fill the hole again if need be...

If it's designed to be fully air tight then the only pressure equalisation must be through the charcoal canister and the canister purge valve into the inlet manifold - the electro-valve is off when the car is parked so presumably there is a pressure relief safety valve somewhere too to stop the tank blowing up like a balloon on a really hot day.

When the engine is running the purge solenoid intermittently opens on a duty cycle - it's not at all clear to me exactly when and how much it opens though - the Lexia reports that it is open a certain percentage (duty cycle modulated) which generally increases with throttle, but I seldom hear it clicking. Then out of the blue one day it will sit there at idle CLICK CLICK CLICK CLICK like a noisy tappet and stop as soon as I rev the engine... so I suppose its possible that the electro-valve is sticky and doesn't actually work reliably... if it stays jammed for long enough it could allow vacuum to gradually develop over a long journey.

Pity its in such an inaccessible place - I really ought to test mine. At the moment I have the purge line input on the throttle body blanked off to rule out air leaks from that system affecting running, however the hose from the electro-valve is open and lying loose in the engine bay - so IF the electro-valve is working it should still be equalising the pressure in the tank, however if it's stuck then the hose being off still won't help the tank equalise.

Ooh, I don't know about the manifold gasket - if the two metallic surfaces are perfectly machined but the gasket isn't perfectly even then there will still be weak spots. The one I took off last week had areas where it had definitely been crushed, but a few areas where the print was still all shiny and new - where it hadn't been clamped as tightly as I would've liked. When fitting the new one I gave all the contacting surfaces a good film of fresh engine oil to try and swell the gasket - this may be as much to do with my improved running as anything else if there were tiny leaks affecting just one or two cylinders. I know I've read of people with consistent problems getting these gaskets to seal, who have ended up using sump-gasket Loctite to create a better seal and had success - maybe these has warped manifolds, or maybe not, but can you be sure yours are perfectly straight...?

I would imagine you've checked all that, but it's one of those things that's easy to assume is "right", when in fact it might not be.

No I've not checked the manifold flanges with a ruler, I really should. Every time I have the manifold out its always a rush to get the job done as I work out in the open at the mercy of the weather. If I had the luxury of a garage I would take my time and be a bit more thorough in my investigations. I have noticed that when I take the manifold out there is usually oil on the faces, even if I've fitted the gasket dry, could that suggest a warped surface that doesn't meet well ? Check the photos in this post:

http://www.frenchcarforum.co.uk/forum/v ... 09#p372309" onclick="window.open(this.href);return false;

Funny thing is when I first got the car there was no gasket there at all - just what remained of some blue silicon (?) sealant of some sort. Guess what - silicon greases or sealants are absolutely forbidden on the inlet system of a car with an oxygen sensor as the silicon kills oxygen sensors... So any additional sealant to help the gasket would need to be mineral based not silicon.

Injector update:

I spent a few hours last night banished to the shed testing the injectors and fuel rail. On initial testing 4 of the 6 injectors were stuck closed. I recorded some video and started to edit it together into one clip and got carried away as I was using it as an excuse to play around with iOS iMovie - and ended up with this standalone video:

" onclick="window.open(this.href);return false;



One injector came right by itself and miraculously was caught red handed un-sticking on camera! The rest took a bit of persuasion - basically leaving the injector timer tool running on constant pulses together with some judicious tapping around the injector housing and each one came free - two fairly easily within a few minutes, the third wouldn't budge even after 20 minutes, until I'd removed the rails from the manifold and given it a few good whacks with a screw driver on the side of the rail near the injector.

Once they were all working I did a balance test and they were not too bad, although one was slightly lower on flow than the others. I then removed all the injectors (after I figured out the technique - a screwdriver on each side simultaneously) and gave them a good clean with carb-clean. All of them had perfectly clear screens although some of them had carbon build-up on the orange plastic bit at the bottom. I also had the regulator and pulsation damper out and flushed out the rails. There was a bit of carbon build-up in the bottom of the holes where the injectors went in.

Two of the injector seal faces were covered in aluminium corrosion from the lower mainfold:



I removed all the bottom orange o-rings and cleaned them up as well as the bottom face of the rails and they all came up fine - greased the o-rings and re-fitted them and I'm sure they'll be fine - they're still nice and soft. The o-rings on the injectors were all greased and the injectors went back in easily with one thumb pressing them.

After everything was back together I added some injector cleaner to my 2 litres of circulating petrol and ran each injector for extended periods of time with fuel pressure. Spray patterns all look good so I then did several balance tests in a row - absolutely spot on (within the margins of error for the technique - its not as good as the method the professional cleaners use with side by side graduated test tubes) no visible difference in flow rates at all. (Dropping from 36 psi to exactly 18 on all 6 injectors on the last test)

All six injectors now sound identical too - they didn't start that way. They sound quite noisy (like injector 1 in the video) but bear in mind that there is no engine noise to drown them out and the speed the timer runs them at (33 Hz) equates to about 2000 rpm. (I think )

I'm now happy to fit them to the car and be reasonably confident that they're not going to be any worse than the ones that are in there now! There is no doubt if I had just swapped them over without doing the work I did to clean up the fuel rail faces and unblock the injectors, that I would have had a massive misfire both from stuck injectors and air leaks around the bottom orange o-ring on two of them.

Over the next few days I'm going to quickly check them on the timer tool to make sure that none of the injectors have stuck again after sitting over night. Quite pleased with the results so far as it was looking very much like I'd have to send these ones away for professional cleaning - one of them was well stuck and wouldn't budge, it was running constantly on the timer tool for over 20 minutes with intermittent tapping from me before it finally let go!

My testing with the scope (see video) shows how you can easily confirm whether an injector is physically moving or is stuck just from the current waveform - now that I have samples of stuck and working waveforms for these particular type of injectors I can easily do an test in-situ on the injectors still in the car with the timer tool and scope and see whether any given injector is sticking or not. I'll bet anything if I do the test on a cold engine that one is initially sticking and causing the misfire I hear when I first start the car.

I'll try to check this before I swap the rails over, and of course I'll do the same battery of tests on the rails and injectors I remove from the car afterwards that I did on these ones.

I've just been out to run another balance test tonight after the injectors have been sitting for 24 hours - no problems with the balance and no sticking either. Looking promising

I also found the cause of intermittent pressure leakage with the pump stopped - with the pump stopped pressure was intermittently dropping fairly quickly - too quickly for me to do the balance test as it requires a stable starting pressure. From pinching hoses I've confirmed its the non return valve in the output of the pump leaking, but only sometimes. I guess the ball valve is pitted or has grit in it so sometimes it doesn't seal quite right. After operating for a while the leakage stops.

That may well explain what I thought was a leaky regulator when I originally swapped the regulators - at the time I was still on the old pump. A small amount of leakage in the non return valve wouldn't affect running though - only cause the pressure to drop if you linger too long between key on and start...and even then it would only momentarily increase cranking to start. Nothing to worry about really given the age of the car!

[stevieb]

If it's designed to be fully air tight then the only pressure equalisation must be through the charcoal canister and the canister purge valve into the inlet manifold - the electro-valve is off when the car is parked so presumably there is a pressure relief safety valve somewhere too to stop the tank blowing up like a balloon on a really hot day.

When the engine is running the purge solenoid intermittently opens on a duty cycle - it's not at all clear to me exactly when and how much it opens though - the Lexia reports that it is open a certain percentage (duty cycle modulated) which generally increases with throttle, but I seldom hear it clicking. Then out of the blue one day it will sit there at idle CLICK CLICK CLICK CLICK like a noisy tappet and stop as soon as I rev the engine... so I suppose its possible that the electro-valve is sticky and doesn't actually work reliably... if it stays jammed for long enough it could allow vacuum to gradually develop over a long journey.

Pity its in such an inaccessible place - I really ought to test mine. At the moment I have the purge line input on the throttle body blanked off to rule out air leaks from that system affecting running, however the hose from the electro-valve is open and lying loose in the engine bay - so IF the electro-valve is working it should still be equalising the pressure in the tank, however if it's stuck then the hose being off still won't help the tank equalise.

Whereabouts is your electro valve? Mine's clipped to the side of the ECU box, so when it clicks is clatters the whole ECU box with it - definitely more than just a CLICK CLICK CLICK

No I've not checked the manifold flanges with a ruler, I really should. Every time I have the manifold out its always a rush to get the job done as I work out in the open at the mercy of the weather. If I had the luxury of a garage I would take my time and be a bit more thorough in my investigations. I have noticed that when I take the manifold out there is usually oil on the faces, even if I've fitted the gasket dry, could that suggest a warped surface that doesn't meet well ? Check the photos in this post:

http://www.frenchcarforum.co.uk/forum/v ... 09#p372309" onclick="window.open(this.href);return false;

Funny thing is when I first got the car there was no gasket there at all - just what remained of some blue silicon (?) sealant of some sort. Guess what - silicon greases or sealants are absolutely forbidden on the inlet system of a car with an oxygen sensor as the silicon kills oxygen sensors... So any additional sealant to help the gasket would need to be mineral based not silicon.

I would take the use of silicon as a bit of an indicator that somebody's either bodged it with silicon because they didn't have a proper gasket (potentially creating the vacuum issues if the mating surfaces aren't perfect), or they've used silicone as an attempted cure after discovering vacuum problems with the regular gasket.

I seem to remember in the depths of the past that UK mechanics were advised in the 70's not to dismantle Japanese motorbike engines whilst they were still warm, because the alloys could be prone to deforming - not in a major way, but enough to cause premature headgasket failure on the re-assembled engine. Maybe our inlet manifold is just as prone - I know I've dismantled mine when it's still been VERY warm to the touch and I've always had the oily patches on the gasket. Strangely though, the oily patches on mine always looked the most compressed - which is why I oiled mine this time - I'm convinced it'll cause the gasket to swell and seal better, but I wouldn't recommend it to anybody until I've confirmed it.

Injector update:

I spent a few hours last night banished to the shed testing the injectors and fuel rail. On initial testing 4 of the 6 injectors were stuck closed. I recorded some video and started to edit it together into one clip and got carried away as I was using it as an excuse to play around with iOS iMovie - and ended up with this standalone video:

" onclick="window.open(this.href);return false;



One injector came right by itself and miraculously was caught red handed un-sticking on camera! The rest took a bit of persuasion - basically leaving the injector timer tool running on constant pulses together with some judicious tapping around the injector housing and each one came free - two fairly easily within a few minutes, the third wouldn't budge even after 20 minutes, until I'd removed the rails from the manifold and given it a few good whacks with a screw driver on the side of the rail near the injector.

Once they were all working I did a balance test and they were not too bad, although one was slightly lower on flow than the others. I then removed all the injectors (after I figured out the technique - a screwdriver on each side simultaneously) and gave them a good clean with carb-clean. All of them had perfectly clear screens although some of them had carbon build-up on the orange plastic bit at the bottom. I also had the regulator and pulsation damper out and flushed out the rails. There was a bit of carbon build-up in the bottom of the holes where the injectors went in.

Two of the injector seal faces were covered in aluminium corrosion from the lower mainfold:



I removed all the bottom orange o-rings and cleaned them up as well as the bottom face of the rails and they all came up fine - greased the o-rings and re-fitted them and I'm sure they'll be fine - they're still nice and soft. The o-rings on the injectors were all greased and the injectors went back in easily with one thumb pressing them.

After everything was back together I added some injector cleaner to my 2 litres of circulating petrol and ran each injector for extended periods of time with fuel pressure. Spray patterns all look good so I then did several balance tests in a row - absolutely spot on (within the margins of error for the technique - its not as good as the method the professional cleaners use with side by side graduated test tubes) no visible difference in flow rates at all. (Dropping from 36 psi to exactly 18 on all 6 injectors on the last test)

All six injectors now sound identical too - they didn't start that way. They sound quite noisy (like injector 1 in the video) but bear in mind that there is no engine noise to drown them out and the speed the timer runs them at (33 Hz) equates to about 2000 rpm. (I think )

I'm now happy to fit them to the car and be reasonably confident that they're not going to be any worse than the ones that are in there now! There is no doubt if I had just swapped them over without doing the work I did to clean up the fuel rail faces and unblock the injectors, that I would have had a massive misfire both from stuck injectors and air leaks around the bottom orange o-ring on two of them.

Over the next few days I'm going to quickly check them on the timer tool to make sure that none of the injectors have stuck again after sitting over night. Quite pleased with the results so far as it was looking very much like I'd have to send these ones away for professional cleaning - one of them was well stuck and wouldn't budge, it was running constantly on the timer tool for over 20 minutes with intermittent tapping from me before it finally let go!

My testing with the scope (see video) shows how you can easily confirm whether an injector is physically moving or is stuck just from the current waveform - now that I have samples of stuck and working waveforms for these particular type of injectors I can easily do an test in-situ on the injectors still in the car with the timer tool and scope and see whether any given injector is sticking or not. I'll bet anything if I do the test on a cold engine that one is initially sticking and causing the misfire I hear when I first start the car.

I'll try to check this before I swap the rails over, and of course I'll do the same battery of tests on the rails and injectors I remove from the car afterwards that I did on these ones.

I've just been out to run another balance test tonight after the injectors have been sitting for 24 hours - no problems with the balance and no sticking either. Looking promising

I also found the cause of intermittent pressure leakage with the pump stopped - with the pump stopped pressure was intermittently dropping fairly quickly - too quickly for me to do the balance test as it requires a stable starting pressure. From pinching hoses I've confirmed its the non return valve in the output of the pump leaking, but only sometimes. I guess the ball valve is pitted or has grit in it so sometimes it doesn't seal quite right. After operating for a while the leakage stops.

That may well explain what I thought was a leaky regulator when I originally swapped the regulators - at the time I was still on the old pump. A small amount of leakage in the non return valve wouldn't affect running though - only cause the pressure to drop if you linger too long between key on and start...and even then it would only momentarily increase cranking to start. Nothing to worry about really given the age of the car!

I love the vid - perfect

I can't wait to see what effect you get from the new injectors. For what it's worth, mine is still running like a dream. I think one of the replacement injectors was a bit sticky at first as the vibration levels increased and there was a definite "cough" from at least one cylinder (like it had been with the factory injectors - it even remained when all six plugs had been changed too), but I've run a couple of £3 bottles of Redex through the last £60-odd of fuel and it's as smooth as the proverbial doo-dah now. Your improvement will be greater that mine and I fully expect to hear your Eureka moment during your first journey all the way down here

With mine, the drone is gone too. Just occasionally I think "hmmm, it's getting loud again", then I check the radio and realise I haven't even turned it on and the bulk of the noise is road and wind noise Take into account that before the recent improvements I had no concept of the level of road noise and you realise how quiet the car now is (though the road noise is a little louder than normal because last summer's Delphi wishbone bushes have turned to marzipan and are wrecking the front wheel alignment - new bushes ordered).

I'm following this thread with even more interest now than before - I want to know how much can be gained by changing/cleaning/improving these "non-serviceable" injectors that everybody seems to be too scared to touch

[lexi]

I am impressed with your Shenanigans Simon and a nice video. What is the little missy saying to this further "work" on the V6?

Not bad temperature wise for shed work? Last year at this time would have frozen you out there.

[Northern_Mike]

I am impressed with your Shenanigans Simon and a nice video. What is the little missy saying to this further "work" on the V6

Mrs. Mandrake must be a very, very patient lady. Mrs. Northern_Mike is amazingly tolerant but she'd have kicked me out by now if I'd done as much work on my car.

Or she's already left and Simon hasn't noticed :-p

Sent from my GT-I9300 using Tapatalk

[stevieb]

Or she's already left and Simon hasn't noticed :-p

[stevieb]

Another quick update on mine. A pootle back up the motorway earlier saw the low fuel light coming on, about 10 or 15 miles from my exit. Knowing that there's at least 80 or 90 miles left in the tank (and the trip computer giving me a range of 74), I carried on so I could fill-up nearer home.

After a few miles of the light being on I noticed a marked increase in exhaust noise (extra noticeable now mine is so quiet) and a slight need for more right boot - the mpg also rose. I think the pump might be dragging air in when the fuel is low or at least changing the way it supplies fuel. I wonder if this is a fault or by design - like I say, the mpg improved, so maybe its a way of eking out the last couple of gallons by forcibly leaning off the fuel supply. Very unlikely I know, but hey, it's French...! Either way, I thought I'd throw this nugget into the mix.