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

Tell us your ongoing tales and experiences with your French car here. Post pictures of your car here as well.

Moderators: RichardW, myglaren

Hell Razor5543
Donor 2021
Posts: 11864
Joined: 01 Apr 2012, 09:47
x 1461

Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Hell Razor5543 »

I would use the PTFE tape as an under layer, followed by a good insulating tape over the top (to stop the PTFE tape coming loose). I would also make sure to have enough tape on either side of the damage to try and limit the possibility of arcing (although it shouldn't happen).
User avatar
Mandrake
Posts: 8414
Joined: 10 Apr 2005, 17:23
x 412

Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Mandrake »

stevieb wrote: I've been through a few more engine bay connectors and earthing points to clean them up and re-mount them - none of them were particularly bad. Then I decided to start the car and see if it ran loud or quiet (and take the opportunity to wiggle the now loose HT leads and see if that made a difference - it didn't). The engine is running noisy, from a cold start, with a return of the top-end clatter/tapping noise I'd had until last summer.

It's almost diesel-like at the minute and quite disturbing. It emanates from beneath the forward area of the inlet manifold so it's got to be either a rear-bank injector or just plain old noisy tappets. I'd always assumed it was a noisy injector seeing as the tappets are hydraulic and shouldn't be noisy, and considering the Terraclean treatment seemed to cure this noise I thought I'd guessed right. I have a spare set of injectors and I think I'm going to have to take the plunge and fit them - or at least the rear three to see what happens...
I've had quite a bit of trouble with noisy hydraulic lifters on mine - at one point I added some wynns hydraulic lifter treatment and they quietened right down on a cold start but one or two are still a bit noisy when hot, in the rear bank I think.

Later I changed the oil and they got noisy again, (!) normally an oil change will quieten hydraulic lifters, its not uncommon for them to be noisy when the oil is in need of changing. The oil that came out was totally black and looked like oil changes have been neglected before I got the car, so I did another oil change a couple of months later, as well as using some lubegard engine flush before draining. Once again the drained oil was totally black after only being in for two months.

This time I put in some fully synth 5w-30 Castrol Magnatec (an oil I had good experiences with on my previous Xantia) and they seem to have settled down now - they're not silent but they're not loud either. At the time when I was experiencing noisy and then quiet lifters there did seem to be some correlation with the timing retard issue, but I could never be sure... because the oil was so black I think I'll do another change in a few months.
Now I get to ask for some help - my ICV hums loudly (so much so I can hear it in the cabin) with the ignition in position II and the engine off. It sounds a lot like it's jammed up against its stop and can't move any further - like a stalled motor - but considering the physical stops inside the barrel of the ICV are beyond the normal operating arc of the inner valve it sounds as if it's being asked to rotate to a position it can't achieve. I noted with the problems I had last summer that this excess noise was a warning that something somewhere was amiss, because some days it was virtually silent and all was well. If yours is still behaving Simon, would you mind telling me if yours hums as well, ideally with a cold engine?
Yes my car is running perfectly again today. My ICV hums and its audible under the bonnet with the engine stopped and the key on, you can also feel a vibration if you put your hand on it. I can't hear it inside the cabin though. I checked it tonight although that was on a warm engine.

I wonder if the supply to one of the two coils is going open circuit when it's noisy ? The way that type of stepper motor works is there are two coils at 90 degrees rotation to each other. Energising only one coil on its own would rotate the stator fully towards that coil, (shaft at 0 degrees relative to an arbitrary reference) energising only the other coil would rotate it fully towards the other coil. (90 degrees) Energising both coils an equal amount would cause it to pull equally towards each extreme causing equilibrium at the half way (45 degree) point.

The ECU drives each coil with a pulse width modulated waveform of opposite duty cycle. For example for a 30% opening one coil would have a 30% on time while the other coil would have a 70% on time. If only one coil was being driven it would probably rotate right around to one of the stops and the vibration of the coil would be transmitted into the housing by virtue of touching the limit stop, thus magnifying the apparent noise and vibration.

When this noisy ICV occurs is it able to regulate the idle though ? Because in the above scenario the idle speed would either be too high or low and unsteady...
And secondly, with the engine running, can you hear the air passing through the ICV? I have a soft hissing sound from that area that might be an air leak, but I think may just be the airflow being strangled a bit too much - it'd be nice to identify which it is.
No, I don't hear any hissing of air around the ICV with all the hoses connected. The easiest way to tell how much air flow there is through the ICV is to disconnect the small hose between the air filter box and ICV at the air filter end - the engine will still run normally.

I find on mine there is a loud hissing/suction noise from the disconnected hose on a cold start (ICV open a lot) but by the time its settled into a hot 650 rpm idle there is barely any flow through this hose at all. In fact if I block the hose under these conditions the idle only drops from 650 rpm to 560rpm - it should drop a lot more than that to the point of a near stall which tells me I have a vacuum leak somewhere else. Also my Lexia ICV valve opening during a hot idle (no accessory load) is only 25% when it should be 30-35%, which tells me the ICV is more closed than normal to make up for a vacuum leak.
EDIT: This was my Coupé Club thread about dismantling an old ICV - http://www.406coupeclub.org/PHPBB3/view ... 83&t=44110" onclick="window.open(this.href);return false; - I'd forgotten just how much metal swarf was stuck to the grease under the plastic cap, not to mention what was stuck to the magnets. This can't be doing it any good, can it? :evil:
When I took my ICV off and cleaned it it wasn't sticky or even dirty really - a little bit of carbon but otherwise clean and moving freely. So for my car at least I don't believe the ICV has been any significant problem.
stevieb
Posts: 265
Joined: 03 Nov 2004, 21:14

Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by stevieb »

Mandrake wrote:I've had quite a bit of trouble with noisy hydraulic lifters on mine - at one point I added some wynns hydraulic lifter treatment and they quietened right down on a cold start but one or two are still a bit noisy when hot, in the rear bank I think.

Later I changed the oil and they got noisy again, (!) normally an oil change will quieten hydraulic lifters, its not uncommon for them to be noisy when the oil is in need of changing. The oil that came out was totally black and looked like oil changes have been neglected before I got the car, so I did another oil change a couple of months later, as well as using some lubegard engine flush before draining. Once again the drained oil was totally black after only being in for two months.

This time I put in some fully synth 5w-30 Castrol Magnatec (an oil I had good experiences with on my previous Xantia) and they seem to have settled down now - they're not silent but they're not loud either. At the time when I was experiencing noisy and then quiet lifters there did seem to be some correlation with the timing retard issue, but I could never be sure... because the oil was so black I think I'll do another change in a few months.
I wish mine was that simple. My oil was changed three times in quick succession less than 12 months ago thanks to a leaky sump that refused to seal at the first two attempts. It was flushed too (the flush made the original minor leak ten times worse :? ), and I only carried out the most recent oil change ten days ago. I used Total Quartz 9000 as specified by Pug, as I found Castrol increased the vibration and noise on mine, and my preferred Mobil is a little expensive. Since I bought the car in 2007 (42k on the clock) this ticking has always been there, regardless of oil changes. The only time it stopped was after Terraclean had done its stuff, which I think is the kicker.

Thinking about it, if your mis-fire was blasting back as far as the throttle-body/air-box hose, it's possible some of that blast found its way back to the crankcase via the breathers - that might explain some of the blackening of the oil so quick - not so much because of heat/flame, but the pressure going the wrong way and forcing carbon and old oil deposits back into the crankcase.

EDIT: Mine is as tappet/clattery as this one http://www.youtube.com/watch?v=SIJcK6O5-xQ. I had the revs dip for a while too. I forget exactly what the cure for this problem was, but I'm sure the new TPS and re-calibration of it went a long way towards it. I imagine low fuel pressure probably doesn't help either...
Mandrake wrote:Yes my car is running perfectly again today. My ICV hums and its audible under the bonnet with the engine stopped and the key on, you can also feel a vibration if you put your hand on it. I can't hear it inside the cabin though. I checked it tonight although that was on a warm engine.

I wonder if the supply to one of the two coils is going open circuit when it's noisy ? The way that type of stepper motor works is there are two coils at 90 degrees rotation to each other. Energising only one coil on its own would rotate the stator fully towards that coil, (shaft at 0 degrees relative to an arbitrary reference) energising only the other coil would rotate it fully towards the other coil. (90 degrees) Energising both coils an equal amount would cause it to pull equally towards each extreme causing equilibrium at the half way (45 degree) point.

The ECU drives each coil with a pulse width modulated waveform of opposite duty cycle. For example for a 30% opening one coil would have a 30% on time while the other coil would have a 70% on time. If only one coil was being driven it would probably rotate right around to one of the stops and the vibration of the coil would be transmitted into the housing by virtue of touching the limit stop, thus magnifying the apparent noise and vibration.

When this noisy ICV occurs is it able to regulate the idle though ? Because in the above scenario the idle speed would either be too high or low and unsteady...
I guess maybe the sound deadening on yours might be better than mine (aren't Citroens renowned for their quietness?) which would explain why you can't hear the humming. I do know that the vibration in mine feels like the rotating valve is tight up against one of the stops. When I dismantled my old ICV I found the physical movement of the internal barrel is about 110°, but the movement required is presumably 90° (fully open to fully closed) - going beyond the 90° point in the closed direction opens up a very narrow slot that may permit enough air to pass through to keep the engine running. And small enough to create a hissing noise too, maybe...
Mandrake wrote:No, I don't hear any hissing of air around the ICV with all the hoses connected. The easiest way to tell how much air flow there is through the ICV is to disconnect the small hose between the air filter box and ICV at the air filter end - the engine will still run normally.

I find on mine there is a loud hissing/suction noise from the disconnected hose on a cold start (ICV open a lot) but by the time its settled into a hot 650 rpm idle there is barely any flow through this hose at all. In fact if I block the hose under these conditions the idle only drops from 650 rpm to 560rpm - it should drop a lot more than that to the point of a near stall which tells me I have a vacuum leak somewhere else. Also my Lexia ICV valve opening during a hot idle (no accessory load) is only 25% when it should be 30-35%, which tells me the ICV is more closed than normal to make up for a vacuum leak.

When I took my ICV off and cleaned it it wasn't sticky or even dirty really - a little bit of carbon but otherwise clean and moving freely. So for my car at least I don't believe the ICV has been any significant problem.
I'd forgotten I'd tested the vacuum some time ago - putting my hand over the hose caused a stall with a very sharp "shoop" noise near the ICV, which I always took to be the L-shaped rubber hose compressing. Either that or it's the brake servo diaphragm being sucked deep into the vacuum chamber.

You're lucky in having a clean ICV - my original one was badly scored and prone to sticking, and the second-hand replacement I'd fitted becomes blackened quite quickly - I only cleaned it a few weeks ago and it had filled with plenty of carbon in the six months since it was previously done. Mind you, as I said before, if your mis-fire was firing back through the inlet it may well have been forcing the carbon back into the crankcase...

I'm going to try another full set of resets/re-calibrations on mine (ICV and both the TPS ones) and see if that helps. Now I know what all these procedures are, it's entirely possible I'm upsetting the parameters. My current job means I get to spend longer periods of time sat in the car and I can see a few ways the TPS could be re-calibrated unintentionally. I shall report back tomorrow.

EDIT 2: Just come across posts on pages 60 and 61 of this mighty thread where you've also tried cleaning up your fuel pump terminals and a whole host of other things I've done recently, Simon. Our minds think alike. This isn't a good thing... :rofl2:

EDIT 3: I knew I'd missed something. This might not show itself quite as much on an auto, but since I switched back to my original coilpack I've had a couple of occasions where a mix of low revs and high gears have caused a "cough". I've only experienced it at those times when I've approached a big open roundabout and I know I don't need to stop, just slow down on the approach, then let it pick back up from 1000rpm in fifth, because it can. The cough doesn't occur until I touch the throttle pedal and isn't accompanied by any noise, but for a split second it feels as though the engine has stalled. There's a definite thump as the engine jumps in its mounts, and then it immediately reverts to normal as if nothing is wrong. It's as if I sometimes catch a weak or missing cylinder - so maybe we're back to sparks or injectors...

EDIT 6,487,265: Rather than messing with the existing one, I wonder if it'd be worth trying another knock sensor on mine and temporarily mounting it using one of the many spare unused bolt-holes on the block or head. It's not ideal, but knowing that the sensor is secure, even if it's past its best, will at least confirm the existing one is fine if nothing changes. If the engine pinks, then it'll be fair to say the replacement sensor either isn't up to snuff or isn't mounted in the best place, but should at least by-pass the unwanted retardation and might help me see how much power I'm losing. I think I'll get stuck into the injector-swap at the weekend, but if that fails I'll give Ade Bingham a try and see if he's got a spare one handy...
User avatar
Mandrake
Posts: 8414
Joined: 10 Apr 2005, 17:23
x 412

Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Mandrake »

stevieb wrote: Thinking about it, if your mis-fire was blasting back as far as the throttle-body/air-box hose, it's possible some of that blast found its way back to the crankcase via the breathers - that might explain some of the blackening of the oil so quick - not so much because of heat/flame, but the pressure going the wrong way and forcing carbon and old oil deposits back into the crankcase.
I think its more likely I was getting bore wash in the misfiring cylinder(s) when I was having problems with an under load ignition misfire. The ignition misfire could cause fuel contamination of the oil past the rings. One reason that I am going to do yet another oil change soon now that I think I've got the misfire under control.
EDIT: Mine is as tappet/clattery as this one http://www.youtube.com/watch?v=SIJcK6O5-xQ. I had the revs dip for a while too. I forget exactly what the cure for this problem was, but I'm sure the new TPS and re-calibration of it went a long way towards it. I imagine low fuel pressure probably doesn't help either...
That's how noisy the hydraulic lifters were on mine when I got it, up until I tried some hydraulic lifter treatment - the very next day they went silent when cold and only a small amount of noise when hot from maybe two of them. (instead of a cacophony of noise from 24 lifters :) )

From what I understand hydraulic lifters get noisy when either the tiny oil feed ways to the them get blocked up (no oil pressure available to "pump up" the hydraulic strut in the lifter) or when the one way ball valve in the lifter has excessive leakage (due to varnish build up) which causes the pressure to leak back quickly instead of being maintained. In extreme cases it can reduce the valve opening time and displacement as the slack has to be taken up by the rocker on each stroke.
I do know that the vibration in mine feels like the rotating valve is tight up against one of the stops. When I dismantled my old ICV I found the physical movement of the internal barrel is about 110°, but the movement required is presumably 90° (fully open to fully closed) - going beyond the 90° point in the closed direction opens up a very narrow slot that may permit enough air to pass through to keep the engine running. And small enough to create a hissing noise too, maybe...
Yes I too noticed that if you turn it too far in the closed direction it actually opens again - presumably it should never go that far in normal operation.
I'd forgotten I'd tested the vacuum some time ago - putting my hand over the hose caused a stall with a very sharp "shoop" noise near the ICV, which I always took to be the L-shaped rubber hose compressing. Either that or it's the brake servo diaphragm being sucked deep into the vacuum chamber.
I keep forgetting yours is a 406, so no only do you have a brake booster attached which I don't, there are other small differences in the air intake system as well. Something to keep in mind when we compare notes...
I'm going to try another full set of resets/re-calibrations on mine (ICV and both the TPS ones) and see if that helps. Now I know what all these procedures are, it's entirely possible I'm upsetting the parameters. My current job means I get to spend longer periods of time sat in the car and I can see a few ways the TPS could be re-calibrated unintentionally. I shall report back tomorrow.
What is your TPS calibration procedure ? I'm sure I've read somewhere how that is done, but I can't remember. Key on for 10 seconds, accelerator flat to the floor for another 10 seconds then key off, or something like that ?

While I don't believe the ICV can be calibrated as such, the TPS certainly can be as the ECU has to learn the minimum and maximum voltages that correspond to closed and full throttle. (Approx 0.7 and 4.5 volts) If a voltage outside of those limits appears even momentarily while driving (for example due to an intermittent connection in the TPS or the wiring harness to it) it would force a false recalibration of the TPS that could affect running.
EDIT 3: I knew I'd missed something. This might not show itself quite as much on an auto, but since I switched back to my original coilpack I've had a couple of occasions where a mix of low revs and high gears have caused a "cough". I've only experienced it at those times when I've approached a big open roundabout and I know I don't need to stop, just slow down on the approach, then let it pick back up from 1000rpm in fifth, because it can. The cough doesn't occur until I touch the throttle pedal and isn't accompanied by any noise, but for a split second it feels as though the engine has stalled. There's a definite thump as the engine jumps in its mounts, and then it immediately reverts to normal as if nothing is wrong. It's as if I sometimes catch a weak or missing cylinder - so maybe we're back to sparks or injectors...
Yep, mine does that same cough where it feels like its trying to stall if I tap the throttle near idle - I even took a video of it here:

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



In that video the engine is idling (not fully warmed up which is why the idle is a bit high, but it does it when fully warmed up too) and all I'm doing is giving the throttle a light but very quick tap with the end of my foot - it takes a bit of practice to get it right but it nearly stalls the engine, which seems to just cut out for a good fraction of a second. I can consistently reproduce it. I'm not snapping it wide open, in fact I'm barely lifting it just above idle - maybe 5% open. It seems to be the suddenness of movement that triggers it not the opening.

Why is the engine nearly stalling when the throttle is quickly opened such a small amount ? I have no idea! :? The obvious answer is the TPS has a dead spot in it, except a couple of months ago I replaced it with a brand new one and there was zero improvement. The other possibility is a problem with the MAP sensor - but that too has been replaced some time ago, and in fact I've re-installed my original MAP sensor recently and there is no difference there either. So I'm baffled.

Because the throttle is being opened such a small amount its not going to be an under load ignition misfire (eg low spark voltage) because the throttle is barely being opened. It's got to be something to do with the mixture/injection and the way the ECU is responding to a sudden change in TPS or MAP reading, except I know its not the ECU either.

This symptom has been there for many months now and not responded to anything I've done and as far as I can see there is no correlation with the engine performing well or performing poorly - the cough is there even when the performance is excellent as well as when its poor.

I am reasonably sure that the same thing that causes the "cough" (momentary cut out) is responsible for the stall/surge cycles that sometimes happen on a hot start - I believe what happens is that the rpm dips a wee bit below idle, the ECU responds by quickly opening the ICV and the sudden increase in air flow instead of lifting the rpm causes this "cough" where the engine seems to cut out, the rpm falls even lower so the ECU opens the ICV even further, after a moment it recovers but by that time the ICV is open quite wide causing the idle speed to surge too high so then it has to close the ICV again, so you end up with a series of over corrections occurring which eventually settles down after about 3 cycles.

Fix the cause of the cough and I'm pretty sure the stall/surge cycles will stop as well. But what is it ???? I have a few ideas for more testing to try to pin down the cause (such as plugging in my old TPS not attached to the throttle body to see if its the increase in air flow or the increase in TPS opening triggering it by controlling them separately, and also seeing whether it coughs with the ICV unplugged) but that will have to wait for more favourable weather.

(I could also put my digital scope on one of the injectors to watch the injector pulse width when tapping the throttle to see whether the injection pulse width is increasing when the throttle is tapped or whether its cutting out - again some nice weather would help there...)

EDIT 6,487,265: Rather than messing with the existing one, I wonder if it'd be worth trying another knock sensor on mine and temporarily mounting it using one of the many spare unused bolt-holes on the block or head. It's not ideal, but knowing that the sensor is secure, even if it's past its best, will at least confirm the existing one is fine if nothing changes. If the engine pinks, then it'll be fair to say the replacement sensor either isn't up to snuff or isn't mounted in the best place, but should at least by-pass the unwanted retardation and might help me see how much power I'm losing. I think I'll get stuck into the injector-swap at the weekend, but if that fails I'll give Ade Bingham a try and see if he's got a spare one handy...
I really wouldn't recommend doing that - the knock sensor is right down in the valley of the V for a reason - its the only place it will pick up knock from all the cylinders, anywhere external you bolt one will not pick up knock reliably, and as its a very high compression engine you run a significant risk of piston damage if you run it for any length of time in a knocking situation...it relies heavily on the knock sensor for safe operation.

I have also thought about attenuating the knock sensor signal slightly before it gets to the ECU with a couple of resistors in an Lpad configuration - in the case of false knock it may provide a clue that a "knock" signal is indeed causing timing retardation, but if the engine really IS knocking due to a mixture problem then I run the risk of damaging the engine. So I didn't try it...(also because its running well most of the time now so I'm trying to leave it alone!)
stevieb
Posts: 265
Joined: 03 Nov 2004, 21:14

Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by stevieb »

Mandrake wrote:That's how noisy the hydraulic lifters were on mine when I got it, up until I tried some hydraulic lifter treatment - the very next day they went silent when cold and only a small amount of noise when hot from maybe two of them. (instead of a cacophony of noise from 24 lifters :) )

From what I understand hydraulic lifters get noisy when either the tiny oil feed ways to the them get blocked up (no oil pressure available to "pump up" the hydraulic strut in the lifter) or when the one way ball valve in the lifter has excessive leakage (due to varnish build up) which causes the pressure to leak back quickly instead of being maintained. In extreme cases it can reduce the valve opening time and displacement as the slack has to be taken up by the rocker on each stroke.
I might have to invest in some of this spangly lifter treatment then, just in case. It might at least save me lifting the inlet manifold unnecessarily.
Mandrake wrote:I keep forgetting yours is a 406, so no only do you have a brake booster attached which I don't, there are other small differences in the air intake system as well. Something to keep in mind when we compare notes...
I guess your brake assist system is all incorporated into the Citroen hydraulics is it, rather than relying on engine vacuum?
Mandrake wrote:What is your TPS calibration procedure ? I'm sure I've read somewhere how that is done, but I can't remember. Key on for 10 seconds, accelerator flat to the floor for another 10 seconds then key off, or something like that ?

While I don't believe the ICV can be calibrated as such, the TPS certainly can be as the ECU has to learn the minimum and maximum voltages that correspond to closed and full throttle. (Approx 0.7 and 4.5 volts) If a voltage outside of those limits appears even momentarily while driving (for example due to an intermittent connection in the TPS or the wiring harness to it) it would force a false recalibration of the TPS that could affect running.
There are three TPS calibrations I'm aware of - one them is a variation of yours and involves key in, position II, throttle flat down, throttle released, key off and out. The other is simply key in and on to position II for 30 seconds, then off and out again. I've tried both in the past, as well as your method, and the only one that has ever resulted in a beep from the dash was yours. However, the other two DO have some effect too, so it's anybody's guess which one is right. I haven't done the reset yet, so I think I'll go and try all three in a bit and see if I get any beeps or other acknowledgements. I wonder if the "ICV reset" we've had success with is actually some kind of TPS reset or calibration - obviously the actions of the ICV are very reliant on the ECU's interpretation of signals from the TPS, so maybe that's the clue.
Mandrake wrote:Yep, mine does that same cough where it feels like its trying to stall if I tap the throttle near idle - I even took a video of it here:

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



In that video the engine is idling (not fully warmed up which is why the idle is a bit high, but it does it when fully warmed up too) and all I'm doing is giving the throttle a light but very quick tap with the end of my foot - it takes a bit of practice to get it right but it nearly stalls the engine, which seems to just cut out for a good fraction of a second. I can consistently reproduce it. I'm not snapping it wide open, in fact I'm barely lifting it just above idle - maybe 5% open. It seems to be the suddenness of movement that triggers it not the opening.

Why is the engine nearly stalling when the throttle is quickly opened such a small amount ? I have no idea! :? The obvious answer is the TPS has a dead spot in it, except a couple of months ago I replaced it with a brand new one and there was zero improvement. The other possibility is a problem with the MAP sensor - but that too has been replaced some time ago, and in fact I've re-installed my original MAP sensor recently and there is no difference there either. So I'm baffled.

Because the throttle is being opened such a small amount its not going to be an under load ignition misfire (eg low spark voltage) because the throttle is barely being opened. It's got to be something to do with the mixture/injection and the way the ECU is responding to a sudden change in TPS or MAP reading, except I know its not the ECU either.

This symptom has been there for many months now and not responded to anything I've done and as far as I can see there is no correlation with the engine performing well or performing poorly - the cough is there even when the performance is excellent as well as when its poor.

I am reasonably sure that the same thing that causes the "cough" (momentary cut out) is responsible for the stall/surge cycles that sometimes happen on a hot start - I believe what happens is that the rpm dips a wee bit below idle, the ECU responds by quickly opening the ICV and the sudden increase in air flow instead of lifting the rpm causes this "cough" where the engine seems to cut out, the rpm falls even lower so the ECU opens the ICV even further, after a moment it recovers but by that time the ICV is open quite wide causing the idle speed to surge too high so then it has to close the ICV again, so you end up with a series of over corrections occurring which eventually settles down after about 3 cycles.

Fix the cause of the cough and I'm pretty sure the stall/surge cycles will stop as well. But what is it ???? I have a few ideas for more testing to try to pin down the cause (such as plugging in my old TPS not attached to the throttle body to see if its the increase in air flow or the increase in TPS opening triggering it by controlling them separately, and also seeing whether it coughs with the ICV unplugged) but that will have to wait for more favourable weather.

(I could also put my digital scope on one of the injectors to watch the injector pulse width when tapping the throttle to see whether the injection pulse width is increasing when the throttle is tapped or whether its cutting out - again some nice weather would help there...)
Ah, mine used to behave like that, but it's been cured (on three occasions) by cleaning the inside of the throttle body with iso-propyl alcohol - it's fine now :wink: .

I had a build-up of sticky tar around the butterfly opening that I guess was either stopping the butterfly from closing properly and upsetting the TPS values at startup (a changeable zero-point), or the tar forms a fine film that briefly stretches over the opening as the butterfly rotates and the ICV closes, momentarily interrupting the air supply. I favour the former, but it's anybody's guess what actually happens. It's a fiddly job to do, but well worth it.

The source of the tar was quickly traced to the crankcase breather that feeds into the filter-box/throttle body hose, and the stickiness can be confirmed without risking damage to the butterfly by poking a finger into that breather hose - it's nasty stuff. Interestingly, I only had this problem re-occurring in quick succession when I used Castrol oil, never having any problems when I used Mobil.

The problem I have now is very different to the above as it only shows under extreme load. Like I said, it only shows in those low revs/high gear moments where the injectors are working harder to enrich the mixture and give me the low-down torque that I'm demanding. If I'm might that my tappet noise is an injector, then this might be revealing an injector that just cannot deliver what's being demanded of it. Whether the demands on the sparks are increased in this situation you would probably know better than me, but if there IS an increase in volts to the sparks I might be forcing a normally less obvious ignition leak to completely ground itself and result in a lost cycle at one or more cylinders. Or maybe it's just a sign that this original coil is incapable of delivering the volts that are being demanded of it...
Mandrake wrote:I really wouldn't recommend doing that - the knock sensor is right down in the valley of the V for a reason - its the only place it will pick up knock from all the cylinders, anywhere external you bolt one will not pick up knock reliably, and as its a very high compression engine you run a significant risk of piston damage if you run it for any length of time in a knocking situation...it relies heavily on the knock sensor for safe operation.

I have also thought about attenuating the knock sensor signal slightly before it gets to the ECU with a couple of resistors in an Lpad configuration - in the case of false knock it may provide a clue that a "knock" signal is indeed causing timing retardation, but if the engine really IS knocking due to a mixture problem then I run the risk of damaging the engine. So I didn't try it...(also because its running well most of the time now so I'm trying to leave it alone!)
Noted. I'd only really thought of doing a few short journeys on local roads with the different knock sensor, just to see if or how things changed. I know some 4-cylinder engines have the sensor at the end of the block and presumably it has no difficulty picking up knocks from the farthest cylinder - whether ours are sensitive enough to sense knocks along our three cylinder length is another matter, but I may keep this idea in the bag in case all other tests fail.
User avatar
Mandrake
Posts: 8414
Joined: 10 Apr 2005, 17:23
x 412

Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Mandrake »

stevieb wrote: I might have to invest in some of this spangly lifter treatment then, just in case. It might at least save me lifting the inlet manifold unnecessarily.
It was the Wynns branded one I tried - I've heard bad things about some of the other brands. I think it was this one:

http://www.halfords.com/webapp/wcs/stor ... yId_255221" onclick="window.open(this.href);return false;

I believe that the main mechanism of operation is that there is something in it that dissolves varnish deposits which can accumulate in the ball valve in the lifters causing them not to seat properly. If they don't seat properly then when the rocker pushes the valve stem down the oil gets squeezed out again instead of hydraulically pushing the valve down - thus lost motion and noise.
I guess your brake assist system is all incorporated into the Citroen hydraulics is it, rather than relying on engine vacuum?
Yes, the brakes are powered by the hydraulic pump that feeds steering, suspension and brakes, which I think is mounted in the same place as the steering pump on the 406. (Down next to the ECU box ?) There is a blanked off spigot on the rear of the inlet manifold facing the firewall which I presume is where your brake booster attaches ?
There are three TPS calibrations I'm aware of - one them is a variation of yours and involves key in, position II, throttle flat down, throttle released, key off and out. The other is simply key in and on to position II for 30 seconds, then off and out again. I've tried both in the past, as well as your method, and the only one that has ever resulted in a beep from the dash was yours.
Interesting that you mention a beep - both in relation to this and the 3x key on/off reset - I've never heard a beep from mine when doing any of these things, but it could just be that there is no equivalent beeper on the Xantia.
Ah, mine used to behave like that, but it's been cured (on three occasions) by cleaning the inside of the throttle body with iso-propyl alcohol - it's fine now :wink: .

I had a build-up of sticky tar around the butterfly opening that I guess was either stopping the butterfly from closing properly and upsetting the TPS values at startup (a changeable zero-point), or the tar forms a fine film that briefly stretches over the opening as the butterfly rotates and the ICV closes, momentarily interrupting the air supply. I favour the former, but it's anybody's guess what actually happens. It's a fiddly job to do, but well worth it.
The interesting thing is I've done exactly that a number of months ago, probably August last year - the throttle body and butterfly was thoroughly cleaned with brake cleaner spray and a soft cloth. It was quite dirty although I wouldn't say it was tarred up, just normal grease and carbon mix. So as far as I know it should be clean, so I don't think that's the cause of the problem for me. :(
The source of the tar was quickly traced to the crankcase breather that feeds into the filter-box/throttle body hose, and the stickiness can be confirmed without risking damage to the butterfly by poking a finger into that breather hose - it's nasty stuff. Interestingly, I only had this problem re-occurring in quick succession when I used Castrol oil, never having any problems when I used Mobil.
I've sometimes wondered how to clean the crankcase breather pipes without too much dismantling of the engine, from memory they're permanently attached to the rocker covers at one end ?
The problem I have now is very different to the above as it only shows under extreme load. Like I said, it only shows in those low revs/high gear moments where the injectors are working harder to enrich the mixture and give me the low-down torque that I'm demanding. If I'm might that my tappet noise is an injector, then this might be revealing an injector that just cannot deliver what's being demanded of it. Whether the demands on the sparks are increased in this situation you would probably know better than me, but if there IS an increase in volts to the sparks I might be forcing a normally less obvious ignition leak to completely ground itself and result in a lost cycle at one or more cylinders. Or maybe it's just a sign that this original coil is incapable of delivering the volts that are being demanded of it...
The required spark voltage to jump the spark plug electrode depends on pressure in the cylinder (at spark time, just before TDC on the compression stroke) and mixture. At idle I believe its around 4000 volts to jump a 1mm spark plug gap. (If the plug was out in fresh air it would be 3000v/mm but there will be some compression above atmospheric pressure even at idle)

Because its a waste spark system both spark plugs are connected in series with the coil in the middle so the coil is generating 8000 volts at idle. (Each plug only sees 4000 though) Under full throttle at low (<2500) rpm you get maximum cylinder pressures near TDC on the compression stroke - this increases the voltage requirement up as high as approximately 30,000 volts. You don't need 60,000 volts from the coil though because the other spark plug is on the exhaust stroke with low cylinder pressures so maybe another 4000 volts or so for the waste spark to jump, for a total of 34,000 volts. To get a reliable spark that doesn't "blow out" as soon as the mixture ignites causing poor combustion the coil/leads etc need a good safety margin - you'd want it to be able to produce 50,000 volts for example. I've measured 60,000 volts from my coil by doing a spark gap test where it can jump about 20mm in the air.

A lean mixture needs a higher spark voltage while a rich mixture needs a lower spark voltage. In fact comparing peak spark voltage under a full throttle snap is a technique sometimes used to identify a cylinder that is running lean because its spark voltage will go much higher than the rest on a throttle snap. For a balanced mixture the spark voltage is proportional to compression pressure so more or less proportional to throttle opening.

If anything limits the maximum voltage you can get a misfire under load. For example say you had a hole in the insulation of the lead and that hole was 5mm away from an earth point. That would need 15,000 volts to jump, so at idle and moderate throttle the spark would jump in the spark plug (only 4000 volts needed) and there would be no misfire, open the throttle more and you'll reach a point where you need more than 15,000 volts, at that point the spark starts jumping through the hole in the lead insulation and not across the gap in the plug! So you get a misfire on that cylinder.

Hard to diagnose because it won't cause problems at idle or light throttle, it can only be tested under heavy load. When driving the car it feels responsive for light throttle openings but when you reach a certain point on the throttle it feels like there is no more to give...

The above description assumes dry air - an insulation breakdown will also cause a general loss of spark voltage in damp conditions, even if the spark doesn't jump directly to the chassis the moisture on the plug wires and in the air itself will cause "leakage" which reduces the spark voltage making the engine more prone to misfire even at lighter throttle - that's where the sensitivity to dampness in the air comes in.

With a waste spark system like this if the misfire is due to low voltage what can happen is that the mixture will not ignite during the compression/power stroke, (not enough voltage to fire the plug at high pressures) but may be ignited on the tail end of the exhaust stroke as the mixture is leaving the cylinder (enough voltage to fire the plug while the exhaust valve is open and the pressure is low) - causing it to burn in the exhaust system... whether this kind of uncontrolled combustion would be detected by the knock sensor I'm not sure, but its at least a possibility.

By the way, my car is still running like a champ yesterday and today, (and the weather has been very wet) aside from the occasional "cough" flicking the throttle from idle, but as I said, there doesn't seem to be a connection between the cough and whether the engine has good performance or not. Perhaps you're right and the throttle butterfly has got gunked up again, I'll have to take a look. I'm off work next week so if the weather isn't too terrible I might be doing a bit of tinkering... :twisted:
stevieb
Posts: 265
Joined: 03 Nov 2004, 21:14

Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by stevieb »

Mandrake wrote:It was the Wynns branded one I tried - I've heard bad things about some of the other brands. I think it was this one:

http://www.halfords.com/webapp/wcs/stor ... yId_255221" onclick="window.open(this.href);return false;

I believe that the main mechanism of operation is that there is something in it that dissolves varnish deposits which can accumulate in the ball valve in the lifters causing them not to seat properly. If they don't seat properly then when the rocker pushes the valve stem down the oil gets squeezed out again instead of hydraulically pushing the valve down - thus lost motion and noise.
Thanks for that - I may give it a try :)
Mandrake wrote:Yes, the brakes are powered by the hydraulic pump that feeds steering, suspension and brakes, which I think is mounted in the same place as the steering pump on the 406. (Down next to the ECU box ?) There is a blanked off spigot on the rear of the inlet manifold facing the firewall which I presume is where your brake booster attaches ?
Yup - that's where the brake booster/servo hose comes off the inlet manifold. The hose is very near identical to the fuel hose ones - stiff plastic and two buttons to squeeze to release the connectors.
Mandrake wrote:Interesting that you mention a beep - both in relation to this and the 3x key on/off reset - I've never heard a beep from mine when doing any of these things, but it could just be that there is no equivalent beeper on the Xantia.
Strangely, mine hasn't beeped once in the last half dozen times I've reset anything. I wonder if it only does it the first time after a full ECU reset (battery off job), or only beeps if the ECU values have been overwritten. I do know I've had occasions where there's been no beep, but things have changed, so I'd guess it might just be a initial calibration thing after the ECU has been wiped.

Mandrake wrote:The interesting thing is I've done exactly that a number of months ago, probably August last year - the throttle body and butterfly was thoroughly cleaned with brake cleaner spray and a soft cloth. It was quite dirty although I wouldn't say it was tarred up, just normal grease and carbon mix. So as far as I know it should be clean, so I don't think that's the cause of the problem for me. :(
As I say, mine was loads worse with Castrol in the crankcase, and I noted earlier that you use Castrol. My old 405TD ran like a dog on Castrol too, and I know their gearbox oil is awful in the manual box (much better to use genuine oil - cheaper too), so I wonder if there's a compatibility issue with the additives in the oil. From time to time people crop up on the Coupé Club from other makes of car and ask about the filters for the crankcase breathers - they're usually somewhat surprised to find there aren't any, and maybe this is why the full PSA spec is only met by a very small number of oils.
Mandrake wrote:I've sometimes wondered how to clean the crankcase breather pipes without too much dismantling of the engine, from memory they're permanently attached to the rocker covers at one end ?
If you mean the small flexible-looking hoses, you'd struggle to clean them without breaking them. They get extremely brittle - to the point one of mine snapped in two places the last time I had the inlet manifold off - I used a length of heatshrink tubing to re-join it - so I think replacement with newer, more flexible items would be the more sensible option.
Mandrake wrote:The required spark voltage to jump the spark plug electrode depends on pressure in the cylinder (at spark time, just before TDC on the compression stroke) and mixture. At idle I believe its around 4000 volts to jump a 1mm spark plug gap. (If the plug was out in fresh air it would be 3000v/mm but there will be some compression above atmospheric pressure even at idle)

Because its a waste spark system both spark plugs are connected in series with the coil in the middle so the coil is generating 8000 volts at idle. (Each plug only sees 4000 though) Under full throttle at low (<2500) rpm you get maximum cylinder pressures near TDC on the compression stroke - this increases the voltage requirement up as high as approximately 30,000 volts. You don't need 60,000 volts from the coil though because the other spark plug is on the exhaust stroke with low cylinder pressures so maybe another 4000 volts or so for the waste spark to jump, for a total of 34,000 volts. To get a reliable spark that doesn't "blow out" as soon as the mixture ignites causing poor combustion the coil/leads etc need a good safety margin - you'd want it to be able to produce 50,000 volts for example. I've measured 60,000 volts from my coil by doing a spark gap test where it can jump about 20mm in the air.

A lean mixture needs a higher spark voltage while a rich mixture needs a lower spark voltage. In fact comparing peak spark voltage under a full throttle snap is a technique sometimes used to identify a cylinder that is running lean because its spark voltage will go much higher than the rest on a throttle snap. For a balanced mixture the spark voltage is proportional to compression pressure so more or less proportional to throttle opening.

If anything limits the maximum voltage you can get a misfire under load. For example say you had a hole in the insulation of the lead and that hole was 5mm away from an earth point. That would need 15,000 volts to jump, so at idle and moderate throttle the spark would jump in the spark plug (only 4000 volts needed) and there would be no misfire, open the throttle more and you'll reach a point where you need more than 15,000 volts, at that point the spark starts jumping through the hole in the lead insulation and not across the gap in the plug! So you get a misfire on that cylinder.

Hard to diagnose because it won't cause problems at idle or light throttle, it can only be tested under heavy load. When driving the car it feels responsive for light throttle openings but when you reach a certain point on the throttle it feels like there is no more to give...

The above description assumes dry air - an insulation breakdown will also cause a general loss of spark voltage in damp conditions, even if the spark doesn't jump directly to the chassis the moisture on the plug wires and in the air itself will cause "leakage" which reduces the spark voltage making the engine more prone to misfire even at lighter throttle - that's where the sensitivity to dampness in the air comes in.

With a waste spark system like this if the misfire is due to low voltage what can happen is that the mixture will not ignite during the compression/power stroke, (not enough voltage to fire the plug at high pressures) but may be ignited on the tail end of the exhaust stroke as the mixture is leaving the cylinder (enough voltage to fire the plug while the exhaust valve is open and the pressure is low) - causing it to burn in the exhaust system... whether this kind of uncontrolled combustion would be detected by the knock sensor I'm not sure, but its at least a possibility.
Interesting. So my low rpm jolt might well be a spark being lost to a leaking plug lead. Hmmm. I think this is a new problem with mine, or an occasional problem that's just got more frequent. It's only done this since I reverted back to the original coilpack, so maybe one coil is failing and both its cylinders are showing the symptoms.

One way I think my problem differs from yours is that with mine I know when the engine is going to be thirstier and slower because tickover is a lot louder and rpm's are just a tiny bit higher. When it's behaving I can barely hear the exhaust note at tickover, I can only just feel a bit of engine vibration, and the high-side of the tacho needle is exactly halfway between 500 and 750. The best bit is that blipping the throttle gets an instant and powerful response, and it sounds positively Jag-like :)

Since the last round of major changes things are tonnes better, but nevertheless when it misbehaves I notice the tacho is slightly higher (only by the thickness of the needle - it used to rise a lot more, but the clean-up of the fuel pump connector cured that), the engine note becomes coarse and raspy, and the vibration increases - most noticeably in the bulkhead and at the pedals. It seems that no amount of wiggling the ignition leads (now freed from their plastic carrier) has any effect on this problem, so unless the leakage is very close to the rear cassette I can't see where it can be leaking, especially if the sparks are demanding such low volts at tickover.

An additional noise sometimes comes into play too, which is a little like an induction howl but nowhere near as loud. It's even there at tickover and it's not coming from anywhere along the inlet path. I'd wondered if it was a breather showing up some blow-by in the cylinders, but there's no pulsing to the sound - I probably ought to record it, because it's so difficult to describe in words.

I guess my problem could be an ignition lead breaking down inside and going high resistance, so if it's in varying states of resistance at start-up (or maybe it's dependant on the first cylinder to fire) the ECU may sometimes try to compensate, and other times be unaware of a problem. Am I right in remembering that the introduction of high resistance will not only reduce the voltage but change the amps being drawn too? If the ECU detected a change in the demand for amps as well as volts, what would it do to compensate?

I still find myself drawn to the injectors though. I bought the car with 42k on the clock, but it was months later when I came to do my first service that I found one of the fuel hose connectors at the filter had been chopped-off and replaced with rubber and jubilee clips, and the three Torx screws in the top of the throttle body were rusting where they'd been spannered, so much so one of them is completely rounded-out. The car was built in early 1999 but not registered until late 2001, so I wonder if the dribble of cheap fuel left sat the tank all that time had gone stale and caused fuel supply issues for the previous owner. My dad worked on British motorcycles and cursed the bikes he got in for restoration that had been stood for any length of time - the tiny drip of fuel left in the jets of the carburettors would set like wax and be virtually impossible to get out. The spannering to the fuel supply can't be a coincidence :?
Mandrake wrote:By the way, my car is still running like a champ yesterday and today, (and the weather has been very wet) aside from the occasional "cough" flicking the throttle from idle, but as I said, there doesn't seem to be a connection between the cough and whether the engine has good performance or not. Perhaps you're right and the throttle butterfly has got gunked up again, I'll have to take a look. I'm off work next week so if the weather isn't too terrible I might be doing a bit of tinkering... :twisted:
Glad to hear it :) Now if only we could work out what that reset procedure actually did! :rofl2:
stevieb
Posts: 265
Joined: 03 Nov 2004, 21:14

Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by stevieb »

A quick update.

I was going to re-fit the other coilpack after leaving it to dry out on a radiator and re-sealing it with epoxy glue, just to see if things would stabilise again with a coilpack change, but it's a bit too wet out there for any work on the electrics.

However, being so damp I decided to try and instigate the suspected spark issues, at least to see if there was any sign of a breakdown inside the leads. Annoyingly the car was in smooth-and-quiet mode so if there is an ignition problem I don't think it was going to show up tonight. I tried listening carefully while I manipulated the HT leads on the off-chance I could cause a cough or splutter, but nothing...

Then I decided I'd get some video of the tappet noise (to be uploaded somewhere later), and realised that waving the light on a mobile phone around the dark engine bay shows up all sorts of places you can get a good listening spot to do the screwdriver-to-the-ear trick - I've done it before in daylight with no real conclusions drawn, but in darkness (and probably with a shift in senses), it was perfect.

Anyway, all four rocker covers just transmit a whirring sound - let's just say the sound matches what we know is happening inside. Then I tried the fuel pressure regulator (or is it the pulsation buffer? The one nearest the throttle body), and the noise was louder and more distinct - a definite ticking rather than a metallic tapping. Then finally I tried the screwdriver on the rear-bank steel fuel rail (the bar that holds the injectors down) at the belt end and nearly deafened myself. There's no doubt it's an injector that's noisy - possibly more than one, though I would imagine that from listening at one end the farthest one would be quieter and sound more like an echo of the nearer one, possibly. Either way, I think it's time I swapped these about and cured it once and for all - it might just be the cause of my power/mpg problem.

Hmmm, I wonder if injectors behave like this if the seals are shot...?
stevieb
Posts: 265
Joined: 03 Nov 2004, 21:14

Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by stevieb »

My noise:

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

The phone mic hasn't picked up any bass, so the V6 rumble is completely missing and making the ticking sound more obvious. However, this video is a good representation of the noise I can hear up the screwdriver from the injector clamp.

In reality, mine sounds more like this one - " onclick="window.open(this.href);return false; - see, it's not just French cars that have problems. The number of Beemers on Youtube with injector problems is quite scary...
User avatar
Mandrake
Posts: 8414
Joined: 10 Apr 2005, 17:23
x 412

Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Mandrake »

stevieb wrote: One way I think my problem differs from yours is that with mine I know when the engine is going to be thirstier and slower because tickover is a lot louder and rpm's are just a tiny bit higher. When it's behaving I can barely hear the exhaust note at tickover, I can only just feel a bit of engine vibration, and the high-side of the tacho needle is exactly halfway between 500 and 750. The best bit is that blipping the throttle gets an instant and powerful response, and it sounds positively Jag-like :)
Are you sure its not your air-con being on or some other accessory load ? Air con being on will raise the idle speed about 50 rpm (so the MP7.0 data says) also if the power steering pressure switch thinks you're turning the steering it will raise the rpm about 100 rpm as well. One other possibility is that according to the MP7.0 data it will boost the idle speed slightly if the ECU detects a low battery voltage to help get it charged up again - I don't know how low it needs to be as I've never observed this behaviour myself.

If none of the above are applying then the only explanation for a higher than normal idle is that either there is a vacuum leak or the ICV is not working properly. Remind me again, do you have a Lexia ? If so on a fully warmed up idling engine check the Idle OCR percentage in the injection menu.

With air con off, steering resting, battery charged, no headlights or other accessories turned on and the idle correct it should be between 30-35%. Mine reads about 25-27% which suggests I have a vacuum leak. 20% ICV corresponds to the ICV valve being completely closed off, so once you get down to 25% there is very little margin of control left, and you're getting close to the point where further turning of the ICV starts to open it up again... (not sure if it can get that far under active ECU control though)

A less scientific test if you don't have a Lexia is to disconnect the ICV feed hose at the air filter and block it with a rag to see how low the RPM drops - it should almost stall, mine only drops from 650rpm to 560rpm.
I guess my problem could be an ignition lead breaking down inside and going high resistance, so if it's in varying states of resistance at start-up (or maybe it's dependant on the first cylinder to fire) the ECU may sometimes try to compensate, and other times be unaware of a problem. Am I right in remembering that the introduction of high resistance will not only reduce the voltage but change the amps being drawn too? If the ECU detected a change in the demand for amps as well as volts, what would it do to compensate?
Nothing at all. These ECU's a very crude by modern standards, there is no misfire monitor (most cars do this by monitoring a high resolution crank sensor signal to detect slow down during the misfiring cylinders phase) and no ECU that I'm aware of monitors the secondary ignition circuit, definitely not this one.

A misfire due to a secondary ignition problem like the spark jumping from an insulation hole or a sooted plug etc is NOT detected by this ECU. There is very little if any change in the primary current ramp when this happens so it has no way to know. A technician looking at the primary current ramp CAN tell if there are certain kinds of secondary problem by looking at very small oscillations at the start and end of the ramp but they are too subtle for an ECU (even a modern one) to analyse or interpret by itself.
I still find myself drawn to the injectors though. I bought the car with 42k on the clock, but it was months later when I came to do my first service that I found one of the fuel hose connectors at the filter had been chopped-off and replaced with rubber and jubilee clips, and the three Torx screws in the top of the throttle body were rusting where they'd been spannered, so much so one of them is completely rounded-out. The car was built in early 1999 but not registered until late 2001, so I wonder if the dribble of cheap fuel left sat the tank all that time had gone stale and caused fuel supply issues for the previous owner. My dad worked on British motorcycles and cursed the bikes he got in for restoration that had been stood for any length of time - the tiny drip of fuel left in the jets of the carburettors would set like wax and be virtually impossible to get out. The spannering to the fuel supply can't be a coincidence :?
Does seem a bit odd - but I've had my fuel rails out before to swap the pressure regulator and there is no sign of tampering with mine, the original click lock connectors are still there.
User avatar
Mandrake
Posts: 8414
Joined: 10 Apr 2005, 17:23
x 412

Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Mandrake »

stevieb wrote:A quick update.
Then I decided I'd get some video of the tappet noise (to be uploaded somewhere later), and realised that waving the light on a mobile phone around the dark engine bay shows up all sorts of places you can get a good listening spot to do the screwdriver-to-the-ear trick - I've done it before in daylight with no real conclusions drawn, but in darkness (and probably with a shift in senses), it was perfect.

Anyway, all four rocker covers just transmit a whirring sound - let's just say the sound matches what we know is happening inside. Then I tried the fuel pressure regulator (or is it the pulsation buffer? The one nearest the throttle body),
That's the pulsation buffer - its just a little diaphragm with some gas pressure (or a spring ?) on one side to cushion and smooth the pressure pulses caused by opening and closing injectors. The pressure regulator is on the left hand end of the front rail. (Looking into the engine bay)
and the noise was louder and more distinct - a definite ticking rather than a metallic tapping. Then finally I tried the screwdriver on the rear-bank steel fuel rail (the bar that holds the injectors down) at the belt end and nearly deafened myself. There's no doubt it's an injector that's noisy - possibly more than one, though I would imagine that from listening at one end the farthest one would be quieter and sound more like an echo of the nearer one, possibly. Either way, I think it's time I swapped these about and cured it once and for all - it might just be the cause of my power/mpg problem.
Without another car to compare with this could be a red herring though - how loud should the clicking on the rail be ? Pretty loud if you're listening with a screw driver stethoscope I'd say. So I'm not sure if this proves anything. I might try this listening test on mine to see what I hear.

By the way, be careful with those injectors, they're about £165 each! :shock: (also the o-rings are rather expensive for a full set)
My noise:

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

The phone mic hasn't picked up any bass, so the V6 rumble is completely missing and making the ticking sound more obvious. However, this video is a good representation of the noise I can hear up the screwdriver from the injector clamp.

In reality, mine sounds more like this one - " onclick="window.open(this.href);return false; - see, it's not just French cars that have problems. The number of Beemers on Youtube with injector problems is quite scary...
Hmm, that noise sounds like noisy hydraulic lifters to me... and sounds exactly like mine did when they were really noisy. (Anyone else care to comment on the noise in the first video as to whether it sounds like lifters or injectors ?)

In the six months since I did the last oil change mine have got a little bit noisier again but they are not as noisy as your video. Where did you hold your phone to capture that noise ? And was that on a hot or cold engine ? I can record mine on the weekend (weather permitting!) with the mic held in the same location to get a comparison.
User avatar
Mandrake
Posts: 8414
Joined: 10 Apr 2005, 17:23
x 412

Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Mandrake »

stevieb wrote:My noise:

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

The phone mic hasn't picked up any bass, so the V6 rumble is completely missing and making the ticking sound more obvious. However, this video is a good representation of the noise I can hear up the screwdriver from the injector clamp.
I've recorded some video of the tappet noise on mine - both cold and hot. Here is cold, taken about 20 seconds after the engine was started after having sat overnight, and still on a fast idle:

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



Don't be fooled by a couple of brief bursts of tapping for half a second - that's the hydraulic pump topping up the suspension pressure after lifting the car. :) I think you'll agree this is very quiet indeed compared to your video, there is only the tiniest hint of a tappet noise, almost inaudible compared to the various other noises, especially when heard in person. (My phone cuts off the bass in the recording too)

Here it is hot - taken after a 30 minute drive and at normal idle speed:

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



I still think its nowhere near as noisy as your video, but there is definitely a nose that sounds like one or two tappets near the middle or left of the rear bank. The front bank seems to be quiet.

Now it could be that the ticking I hear when its hot is not actually tappets but perhaps an injector that is becoming noisy when hot ? Hard to prove though as you can't disconnect the rear injectors with the engine running like you can the front ones... :?

On the basis of "why not" I decided to put some of the Wynn's treatment in today to see if I can get rid of the ticking when it's hot. (The videos were both taken before it was added)

I've only used it once before and that was adding it to dirty oil before any oil changes had been done, it's had two oil changes since then so it may be more successful if its starting with cleaner oil.

Before I applied the first Wynn's treatment it sounded very noisy like yours both cold and hot, after treating it it became silent when cold but slightly ticky (as in the second video above) when hot.

After I did the first oil change (I put in Mobil Super 2000 10w-40, semi-synth, which I was not impressed with) it got noisier again and stayed noisy for the two months that oil was in, I then changed it for Castrol Magnatec 5w-30 fully synth and it gradually got quieter again until the point where its silent when cold but still ticking a bit when hot - as in the above videos.

Will be interesting to see if a second treatment does anything - if not I wonder if it could indeed be something else like an injector that becomes noisy when hot... it's a possibility I suppose.

BTW the car's performance has been mixed today - a bit sluggish at first but running well when its wound up, and ok again by the time I was heading home. As I do such ridiculously short trips during the week its hard to know whether that is a factor. It was also raining hard today while I was out.
stevieb
Posts: 265
Joined: 03 Nov 2004, 21:14

Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by stevieb »

Blimey, lots to follow-up on. I'll try to keep keep the response a manageable size :)
Mandrake wrote:Are you sure its not your air-con being on or some other accessory load ? Air con being on will raise the idle speed about 50 rpm (so the MP7.0 data says) also if the power steering pressure switch thinks you're turning the steering it will raise the rpm about 100 rpm as well. One other possibility is that according to the MP7.0 data it will boost the idle speed slightly if the ECU detects a low battery voltage to help get it charged up again - I don't know how low it needs to be as I've never observed this behaviour myself.
No accessories are on at all. You might be making a valid point about battery voltage though - maybe I need to check my terminals. They should be okay though, as the battery is only a little over a year old and I cleaned-up the terminals and clamps when I fitted it, including my trick for getting the positive clamp to fit the undersized terminal on the battery (a length of 15mm copper pipe cleaned inside with a file and some wire wool, cut to length, then split along that length so its diameter can be reduced - it works well :lol: ). As I say though, my increase in tickover rpm during problem time is miniscule, especially when compared with the large increase in noise which is excessive. I think the key word is noise. It's smooth when it's behaving - it's rough and angry-sounding when it's not.

I don't have Lexia, but the vacuum test (repeated again this afternoon) is successful - there are no vacuum leaks. Mind you, this is with the car having behaved well for a few days. Maybe I have got a leak, but it's intermittent. I guess I need to repeat the vacuum test when things are bad.
Mandrake wrote:Without another car to compare with this could be a red herring though - how loud should the clicking on the rail be ? Pretty loud if you're listening with a screw driver stethoscope I'd say. So I'm not sure if this proves anything. I might try this listening test on mine to see what I hear.

By the way, be careful with those injectors, they're about £165 each! :shock: (also the o-rings are rather expensive for a full set)
I have a spare set of six injectors :wink: I picked them up from Ebay last year, still mounted in their rails, so I have the full set of spare fixings and bolts etc. The injectors were pretty easy to extract from the rail too, so I don't have too much fear with them. I'm more concerned with lifting the inlet manifold - that job always fills me with a certain sense of dread.

I don't know how loud the clicking should be, but the rear rail is a LOT louder than the front through the screwdriver stethoscope (I like that phrase :P ), and all four rocker covers are almost silent, at least as far as ticking is concerned - let's just say when listening at the rocker covers that with the screwdriver to my left ear, the ticking was louder in my right ear. I do agree that it sounds very much like tappets, but none of my oil changes in almost seven years have affected this noise, yet the Terraclean super-doooper fuel system treatment silenced it for a few months. I would've said this was due to almost an hour at a very high tickover clearing the oilways, but I regularly give the car an Italian tune-up and it gets plenty of motorway miles, so it can't be that.

I recorded a new video today which I'll upload to Youtube shortly. I've filmed it a lot like yours Simon, so you'll see where the camera goes and hear where the noise is coming from. Again, the bass is completely absent (the giveaway being the lack of exhaust note before I lift the bonnet), but the directionality of the mic means it really helps pin-point the source of the noise.

When the car is misbehaving, the tappety/injectory noise is audible with the bonnet closed, and at its worse is audible inside the cabin, along with the massively increased exhaust note. This is my biggest argument for the power/mpg problem and the tappet noise being caused by an injector rather than HT leads and/or tappets - they appear to be inextricably linked. If it IS tappets, then it's undoubtedly the inlet cam on the rear bank - which would make sense as this one gets the least amount of natural airflow, so would probably be more prone to problems - but then again this is in the same vicinity as the injector(s) I'm suspecting... :?

Right. Time I headed over to Youtube to upload this video in-between watching sticky injector videos that also sound like our tappet noises... :)
stevieb
Posts: 265
Joined: 03 Nov 2004, 21:14

Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by stevieb »

Today's video is here http://youtu.be/Ut6-H_4aJoo

Of course, the one thing I haven't said above is that I might have tappet AND injector noise, which would certainly explain why it's so loud.

I can certainly hear the distinctive 'ticking' sound that Youtube injector noise videos seem to capture (but is a little lost in my videos) - I find it to be more of an electronic tick (like a spark plug sparking - that short, sharp tick noise), rather than the definite metallic sound of tappets. You see, I wonder if one of mine is a bit gummy and sometimes dribbling rather than spraying. This would definitely cause the engine note to change and might even result in a certain amount of unburnt fuel finding its way into the exhaust and igniting there, causing the rough, growly noise I hear when things are bad. I know that even after a long motorway journey, if I find my way into some town traffic when the noise is there I also see a lot of vapour still coming from the exhaust - you wouldn't normally expect this from an exhaust that's well and truly warmed-up.

I think it's as you've found Simon, anything less than ideal combustion gets detected by the oxygen sensor and results in the ECU making changes elsewhere to compensate. As you say, it's pretty crude :?

Ooh, before I go. This last week, although the power/mpg problem hasn't been too bad, I've noticed subtle fluctuations whilst out on the road which I never had before - things are varying ever-so-slightly mid-journey, which is new. Before this, I only ever noticed changes between shutdown and startup, even to the point I could start the car, hear the noise, knock it off and start again, and it'd be quiet.

I've also confirmed that starting the car up instantly is far better than turning the key, pausing in position II, then starting. Is it possible the ECU (being late 90's technology) takes a few seconds to retrieve its learned parameters from 'RAM' (the RAM that loses its data when the power supply, i.e. the battery, is disconnected)? And if you fire it up before it's had time to load them it reverts to using factory default parameters and learning from scratch again? That might explain it...

Since I refitted my original coil pack I can now feel the injectors close too - it's quite a distinctive sensation which is also new. I noticed it straight away with this last coil pack swap, but it didn't occur to me what the cause was until I read the bit about the injectors closing at 1100/1400rpm, otherwise I would've thought it was a placebo effect - I actually feel it at exactly the right rpm, and under the exact same criteria, so that bit seems to be working correctly, but something else is working incorrectly for me to be able to feel it. I wonder whether the engine-braking-drone I get is down to an injector not fully closing. If the ECU thinks the injectors are closed I imagine the spark also goes to low volt (assuming it doesn't stop completely), and if this is too low to ignite the dribbly mixture the unburnt fuel ignites in the exhaust creating the extra noise.
stevieb
Posts: 265
Joined: 03 Nov 2004, 21:14

Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by stevieb »

These are my three front plugs Simon - how do they compare with yours?

Image Image Image

I've switched back to the secondhand coilpack now the cracks are sealed with epoxy. The 2k-3k rpm drone was getting annoying on the other one, so I thought I'd see what difference it made. Tickover was immediately quieter and smoother with no other changes being made (though it took a bit more spinning over before it fired - maybe the time required for the coils to reach working voltage).

The lovely smooth tickover and throttle blip is in this video - " onclick="window.open(this.href);return false; - I just wish the mic could capture the bass.

This video is the latest tappet/injector noise one - " onclick="window.open(this.href);return false; - again, it exaggerates the noise a LOT. The description says how I filmed it and what's what.