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

[Mandrake]

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

I'm not going to say this car hasn't caused a few arguments... but they stem mainly from the mistaken belief that non technical people tend to have that the entire running costs of a car is tax, insurance, and fuel, (with monthly costs only being fuel) and that you just drive it until it breaks down - and if its not breaking down why are you spending money on it. I'm sure we've all had that discussion with significant others before. Trying to explain that regular maintenance spread out evenly across the year (instead of a massive bill out of the blue when something major breaks or at MOT time when half a dozen expensive fails occur) usually falls on deaf ears.

To me it makes sense that jobs that need to be done soon but aren't urgent are spread out so you're doing a bit each month rather than waiting for a lot of things to get urgent then spending a large sum of money one month... but spreading it out this way just makes it seem like "every month its something", so I can't win.

Even on a relatively new car this kind of short sighted thinking only postpones the inevitable, and dealer servicing on a lot of newer cars is NOT cheap either. (A work colleague just had the clutch on their 3 year old 30,000 mile regularly dealer serviced mini fail catastrophically a month outside warranty - the repair cost was £1200 but after a lot of wrangling and complaining mini agreed to pay 90% of it as it was only just out of warranty - my suspicion is its a known flaw...) You might not be paying for servicing every month but when you go in for a regular service you get well and truly whacked.

The thing is while I have had a lot of trouble with this car I wasn't bargaining on, none of its problems have really cost me that much money compared to basic running costs like petrol/insurance etc, and some of the costs (unneeded parts) have occurred due to my own inexperience and lack of facilities to diagnose these type of problems and initial unfamiliarity with this engine/gearbox. This car was a bit of a leap into the unknown for me. It's mainly the aggravation, stress and my time spent working on it that has been excessive. If I'd been paying someone else to try and fix it then it would have cost a fortune, or rather it would have been scrapped as uneconomic to fix!

It's been a learning experience, and I've learnt a hell of a lot about troubleshooting and diagnosis of engine/gearbox problems in the process, which I don't regret. I didn't even know what an oxygen sensor was before I bought this car, let alone how it worked!

So yes, I haven't had the best run with this car but all the same arguments over cars and money that happened with this car would have occurred with any car over about 10 years old that needs regular spread through the year maintenance, which can't be counted on to (at least temporarily) just keep going with only fuel month after month... people just need to understand that at the end of the day maintenance costs ARE one of the running costs of a car, even though they don't appear regularly on a newer car... driving until stuff breaks generally costs more in the long run, especially if its something like an auto gearbox blowing up through neglect of oil changes, or a CAT melting due to neglecting misfire problems!

[Mandrake]

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

Not bad at all. I was in jeans, sweatshirt and a jacket but I wasn't cold at all and I was working until about 9:30 at night... most unusual for winter! No sign of snow, I don't think we'll get any this winter...

I even have high hopes that this weekend will be fine (so says the weather report) so I can get this newly serviced set of injectors and rail swapped into the car, which I think will be a couple of hours work.

I've decided that while I'm at it I'm going to replace the coolant expansion chamber with the leaky seam as its far easier to get at while the manifold is out. Should only be an extra 15 mins work or so in theory... Given that a brand new expansion chamber is only £40 inc VAT I really have no excuse not to have replaced it already. Last thing I want is to boil the heads due to running with the pressure cap loose all the time...I've been ok so far but best not to tempt fate any further especially when other problems are finally being resolved and she's actually running pretty well...

[Mandrake]

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

It's inside the front left wing near the battery. The hose runs along past the battery and then into a hole in the inner skin on the left wing, inside the wing is the electro-valve and the charcoal canister. From underneath the car with part of the wheel arch lining off you can see the bottom of the charcoal canister but I haven't been able to see the electro-valve as I think its above the canister. (I haven't tried hard to reach it though)

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 think it was probably a case of someone took it apart not realising they needed a new gasket, ripped the gasket on removal (which is really easy to do) and had to bodge it back together with some sealant. Funny thing is the car ran really well for many months like that (maybe years) but by the time I took the manifold out the first time there was hardly any of the sealant left. Perhaps the sealant deteriorating and introducing vacuum leaks was the beginning of some of the running problems I had ?

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.

Yep, I've taken my inlet manifold out when its quite hot too - still a wee bit too hot to touch when I started the job. Interesting that your gasket always has the oil on it too, maybe that's nothing to worry about then. I still think I have a small vacuum leak, and if its on an individual inlet runner its certainly going to upset the idle as one cylinder will idle lean. Note sure if you saw this thread:

http://www.frenchcarforum.co.uk/forum/v ... =3&t=47659" onclick="window.open(this.href);return false;

I've ordered some Hylomar universal blue to smear on the new gasket when I refit it - it may not be leaking after all but I like the idea of some extra insurance.

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

Yes its Redex that I use too, I've noticed that I've had to use it at about twice recommended strength to get an obvious change though. Great to hear that it worked for you.

While bench testing these second hand injectors I added a very strong dose of Redex - only about 50mL, but as there is less than 2 litres of fuel that's around 20-30 times normal strength that you would add to a fuel tank. Enough that the petrol in my test rig changed from green to pink. The effect was very quick - one injector was slightly down in flow before adding it, (only about 5% actually) after adding that high concentration and running each injector on continuous pulsing for a couple of minutes each they're all now perfectly balanced.

Of course I wouldn't recommend such a strong dose in a car - the engine probably wouldn't take kindly to running on such high doses of what is probably mostly kerosene... and I've read that high doses of injector cleaner can cause problems with the fuel system in the long term. But on my test rig its just squirting into a tray so no harm done in the engine, and I think the super high concentration does effectively dissolve the varnish out of the pintle valve, with varnish deposits being the main thing that goes wrong with an injector and causes it to stick or have low delivery. (Build-up of varnish even if it didn't cause it to stick would still reduce the effective opening aperture) Certainly there was nothing wrong with the screens on these ones.

[Mandrake]

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.

I doubt whether its by design. I would say you're probably right that you're getting a few bubbles of air in the fuel, possibly the swirl pot valve is not working on your pump assembly, causing some air ingress when the level gets low in the tank.

I notice with my second hand fuel pump that when I get down to the warning light (about 10-15 litres left) that it doesn't run quite as well, and very occasionally I'll get a complete cut out for a few seconds under hard acceleration up a hill, where I think the pump is being starved for fuel. I'll literally be accelerating hard then with a large jolt there will be no power at all for for about 2-3 seconds then suddenly it will come back again. Only when the tank is low on fuel. (Not THAT low though, still 15 litres left)

I never had that problem with my original fuel pump so despite the intermittently leaky non-return valve I'm thinking about putting my original fuel pump back in. (Not a high priority though) I think the problem is the rubber bung at the bottom of the swirl pot leaks so when the fuel in the tank is very low the level in the swirl pot instead of being right at the top drops down lower - on my testing on the bench with the injectors I've noticed the pump starts generating a lot of turbulence and bubbles if the level in the pot gets below about 3/4 full, so anything that causes the swirl pot level to drop too low is going to cause problems especially during heavy acceleration or cornering where the fuel in the main tank is temporarily thrown away from the pump - in those conditions the car is running entirely on the less than one litre in the swirl pot!

[stevieb]

I doubt whether its by design. I would say you're probably right that you're getting a few bubbles of air in the fuel, possibly the swirl pot valve is not working on your pump assembly, causing some air ingress when the level gets low in the tank.

I notice with my second hand fuel pump that when I get down to the warning light (about 10-15 litres left) that it doesn't run quite as well, and very occasionally I'll get a complete cut out for a few seconds under hard acceleration up a hill, where I think the pump is being starved for fuel. I'll literally be accelerating hard then with a large jolt there will be no power at all for for about 2-3 seconds then suddenly it will come back again. Only when the tank is low on fuel. (Not THAT low though, still 15 litres left)

I never had that problem with my original fuel pump so despite the intermittently leaky non-return valve I'm thinking about putting my original fuel pump back in. (Not a high priority though) I think the problem is the rubber bung at the bottom of the swirl pot leaks so when the fuel in the tank is very low the level in the swirl pot instead of being right at the top drops down lower - on my testing on the bench with the injectors I've noticed the pump starts generating a lot of turbulence and bubbles if the level in the pot gets below about 3/4 full, so anything that causes the swirl pot level to drop too low is going to cause problems especially during heavy acceleration or cornering where the fuel in the main tank is temporarily thrown away from the pump - in those conditions the car is running entirely on the less than one litre in the swirl pot!

Well my drone was definitely back this morning, along with a much lower mpg and loss of power, but I'd only put £20 in so maybe not enough to completely purge any air out of the swirl pot. It eased during the day, then returned as the level dropped. I think you may well be right about bubble getting into the system. I wonder if the jolt that I was suffering until recently was related...

One thing I forgot about yesterday is that the fuel gauge misbehaved again. After 60-odd miles the gauge hadn't moved. A minor detour into services (and a stop/start of the engine), saw it drop to where I'd expected it to be. After that it carried on dropping normally. Could this be linked somehow? It was a regular problem when the pump connector was still corroded, but I thought the clean-up had fixed it. Time for a new pump...?

[stevieb]

Yep, I've taken my inlet manifold out when its quite hot too - still a wee bit too hot to touch when I started the job. Interesting that your gasket always has the oil on it too, maybe that's nothing to worry about then. I still think I have a small vacuum leak, and if its on an individual inlet runner its certainly going to upset the idle as one cylinder will idle lean. Note sure if you saw this thread:

http://www.frenchcarforum.co.uk/forum/v ... =3&t=47659" onclick="window.open(this.href);return false;

I've put my mark on that thread

One thing worth trying if you think you've got a vacuum leak and you've got a can of carb cleaner spare, is to spray the carb cleaner close to all the likely sources - you'll hear a change in engine note if the engine is dragging it in. If you partly block the airway through the ICV you might be able to force the vacuum to reveal itself. Maybe try it after dark with a narrow beam of torch light shone through the mist of carb cleaner - you might be able to see any turbulence and begin to pinpoint the precise location from there.

[Hell Razor5543]

Have you tried cleaning the in-tank filter? I wonder if you have a build up of crud that could restrict the fuel flow, and disrupt the fuel gauge?

[stevieb]

Have you tried cleaning the in-tank filter? I wonder if you have a build up of crud that could restrict the fuel flow, and disrupt the fuel gauge?

That's one thing I've not tried. I know the pumps can be a pain to get out and often need new seals, so I've been putting it off until I'm certain I need to replace it. Cleaning that filter might turn out to be a job for the weekend though, if the weather is good (like Simon, I work outside too - just a little farther from the Arctic Circle than him ).

[Hell Razor5543]

According to items I have read on the forum, doing this when the tank is close to empty is useful, otherwise it gets awkward and messy. Somebody on the forum had dimensions for a wooden spanner (to protect the plastic nut from damage).

[stevieb]

Cheers HR - I'll look it up at the weekend, subject to weather

[Mandrake]

Well my drone was definitely back this morning, along with a much lower mpg and loss of power, but I'd only put £20 in so maybe not enough to completely purge any air out of the swirl pot. It eased during the day, then returned as the level dropped. I think you may well be right about bubble getting into the system. I wonder if the jolt that I was suffering until recently was related...

If you get a big gulp of air and no fuel for a second or two in the fuel line the engine will completely cut out then suddenly spring to life again - if it happens under hard acceleration in a low gear as it has to me a couple of times it causes an almighty jolt that throws you forward in your seat. It's as if you turned the key off under full acceleration.

One thing I forgot about yesterday is that the fuel gauge misbehaved again. After 60-odd miles the gauge hadn't moved. A minor detour into services (and a stop/start of the engine), saw it drop to where I'd expected it to be. After that it carried on dropping normally. Could this be linked somehow? It was a regular problem when the pump connector was still corroded, but I thought the clean-up had fixed it. Time for a new pump...?

Pumps are too expensive to replace without hard evidence - I was sure mine was playing up and, well, after obtaining a second hand one, it turns out it wasn't. Now I have two pumps Don't get me wrong - without the spare pump my injector cleaning and testing wouldn't have been possible, but it's just one more of a long list of not-really-required parts, so I would hold off replacing yours if I were you.

Maybe try to clean the connector again with some proper contact cleaner as there's not much that can go wrong with the fuel level sender if you've had a look at how they're made!

[Mandrake]

One thing worth trying if you think you've got a vacuum leak and you've got a can of carb cleaner spare, is to spray the carb cleaner close to all the likely sources - you'll hear a change in engine note if the engine is dragging it in. If you partly block the airway through the ICV you might be able to force the vacuum to reveal itself. Maybe try it after dark with a narrow beam of torch light shone through the mist of carb cleaner - you might be able to see any turbulence and begin to pinpoint the precise location from there.

Hey, good idea with the carb cleaner - why didn't I think of that ? I already knew of the technique but haven't tried it before and didn't think of it recently. I still have half a can too after using it to clean the injectors and rail.

Have you tried cleaning the in-tank filter? I wonder if you have a build up of crud that could restrict the fuel flow, and disrupt the fuel gauge?

That's one thing I've not tried. I know the pumps can be a pain to get out and often need new seals, so I've been putting it off until I'm certain I need to replace it. Cleaning that filter might turn out to be a job for the weekend though, if the weather is good (like Simon, I work outside too - just a little farther from the Arctic Circle than him ).

The pump is a real pain to get out - take it from me. The hard bit is getting the large plastic ring undone and also done back up again.

You're supposed to have a multi-pronged tool which can grip the ridges and turn it around like a big jar lid on a preserving jar (that's basically what it is) but of course I didn't have that and was impatient to swap it so I managed (barely!) to get it undone by pushing and hammering on two 180 degree opposing ridges simultaneously with two large flat blade screw drivers.

Trying to hammer it around with a single flat blade screw driver is completely impossible. Hammering it around with two screw drivers at 180 degrees is just barely possible but very difficult (especially on your own) and I would not recommend trying to do it this way on your daily driver. It's easy to snap the plastic ridges off and if you have it part undone you might not be able to do it up again and then you'll have a petrol fume leak into the car. I got lucky, but it was only luck.

Once you have the ring unscrewed the job isn't too difficult - a large o-ring sits under the edge of the ring, mine was absolutely fine so I just greased it and reused it and I haven't had any leaks. The tank needs to be empty down to the warning light being on otherwise you will spill petrol all over the carpet under the seat. Even when nearly empty unless it has sat for a long time the swirl pot will be full of petrol, and to lift the pump unit out and allow both the inlet sock and the swinging arm and float clear the hole you have to tilt the whole assembly at about a 30 degree angle - which if its full of petrol will spill.

So have a small hose ready to syphon the petrol out of the swirl pot before you finish extracting and tilting the assembly. Again I was lucky and didn't spill anything but I can see how easily it could turn into a big mess.

On reassembly I greased the o-ring as otherwise its impossible to do the ring up fully again - even then it was still a real struggle to get the ring fully tightened. (or indeed judge what fully tightened was) The proper tool for the ring would certainly make the job 10x easier.

Have you tried cleaning the in-tank filter? I wonder if you have a build up of crud that could restrict the fuel flow, and disrupt the fuel gauge?

There are two in tank filters - one is a sock shaped like a wedge that sticks out from the bottom edge of the swirl pot assembly, the other is a small sock on the bottom of the motor itself. On mine both were clean and to be honest looking at how they're made I think its very unlikely that they will be clogged unless the fuel tank is absolutely filthy.

[Mandrake]

Another progress report.

On Saturday I swapped the injectors and rails over as well as replacing my leaky coolant expansion chamber, and while I was at it I fitted the green coolant temperature sensor I bought a year ago but never got around to fitting. I don't think the old one was faulty, but why not - its about two minutes work when the air filter box is out and I already had the coolant drained down to the level of the expansion chamber hose. I wish I had the blue and brown coolant sensors handy or I would have changed those as well - the one that drives the fans occasionally kicks the fans into high speed for a few seconds when the engine is nowhere near overheated...(oh well, next time)

Its been running 5 days with the coolant pressure cap tight (previously I was running it with the cap loose otherwise I lost coolant) with no leakage or loss of coolant so far. After a longish drive today then the car left sitting about an hour I checked it and there was a good but not excessive "fssst!" of pressure left when I opened the cap and the level was exactly right. So job well done there and I wish I'd done it sooner, it was an easy job and the expansion chamber is not that expensive!

Changing the rails over was a long day and I ran into a couple of snags. Although I managed to get the old rail out without breaking the front cam box breather tube, (and feeling rather pleased with myself for not breaking it) on attempting to fit the replacement rail as I very gently bent the breather just enough to clear the rail there was a loud CRACK! and it snapped clean in half just down below where the hose goes between the two rails.

Of course when I went to get my heat shrink I discovered I didn't have any big enough! I was now stuck at home late on a Saturday afternoon with no transport available other than a Taxi and no immediate idea of where I could get some suitable heat shrink. So I managed to cobble together an alternative - a piece of 12.7mm ID thin wall hydraulic hose was pressed into service as a joiner sleeve - it was a snug fit, I added a bit of Hylomar blue as a sealant and a couple of tiny hose clamps and it seems to have made a strong, seemingly air tight join.

On taking the old rail out I discovered to my horror that the hose between the two rails had a big split/gouge in it that looked like it surely must have been almost right through. There is no way I would have refitted it like that so it was a good thing after all that I had a full rail and not just a set of injectors! I didn't damage the hose during removal as I noticed it before I'd removed it, and I don't think I've damaged it during previous work either, so it was possibly a ticking time bomb that has been there for a while...

On refitting the manifold I put a good smear of Hylomar blue on both sides of the manifold gasket, and I have to say it looks the stuff - it has just the right sticky but non setting consistency to give an air tight seal, but shouldn't be too hard to remove next time. Of course only after everything was put back together I noticed the little rubber blanking tube on the right rear of the manifold had split right down the middle. So a bit of vacuum line with a bolt pushed into the end is now serving as a blanking tube. The canister purge line which has been disconnected and blanked off at the throttle body for the last month was reconnected. (More on that later)

So how does it run now ? A little bit underwhelming to be honest. Not really any worse, but not the improvement I was hoping for. The tappets are still silent when cold and the same two tappets as before are noisy when the engine is hot - I now know its not noisy injectors as I've completely changed the injectors and the noise is exactly the same and in the same locations...(I did think it was tappets originally so this just confirms that)

I think the vacuum leak may be gone - when I block the ICV hose now the engine completely stalls, (as it should) previously it would still idle at 560 rpm with the ICV hose blocked. I can't tell for sure whether the vacuum leak is completely eliminated until I get my Lexia back and look at the ICV OCR percentage.

It could be that a split was developing in the rear blanking tube for some time so if the vacuum leak is fixed I don't know if its the blanking tube or whether its adding sealant to the gasket. Then of course I have the wild card of the repair to the cam box breather hose - I don't know how well that will last or whether it will start leaking. (I now have some large heat shrink should it need redoing)

The misfire I was getting for the first 10-20 seconds after a cold start now seems to be gone too. It starts and idles smoothly straight away now. Also when fully warmed up after driving the idle is also dead steady and smooth now, it wasn't like that before. I haven't had time to test the old injectors but it looks like there might have been some imbalance or intermittent sticking, or perhaps a vacuum leak on an inlet runner. Hard to say. I decided against taking the spark plugs out for inspection as I remembered at the last minute my torque wrench is a half inch drive and I don't have a half inch to 3/8" adaptor to allow me to use it with my plug socket. Doh!

Symptoms that didn't change include the stumble when flooring it from idle and the near stall when tapping the throttle quickly but lightly at idle. The near-stall/surge cycles which sometimes occur after a hot start when the car has sat for 10 minutes is still very much in evidence too, although I think I have figured out what causes that common problem. (That's a story for another post)

Yesterday I decided it was time to investigate the dodgy oxygen sensor further and see if I could identify any mixture problems - so I made a test lead that allows me to back probe the oxygen sensor connector and safely run that test semi-permanently into the cabin so I can see the oxygen sensor waveform on the dashboard while driving. Quite enlightening!

The first thing is it confirmed 100% my belief that the O2 sensor does not warm up properly from the in built heater. (which is less than half the wattage of the correct type) Two minutes of idling from a cold start and there is no activity from the sensor at all, three minutes of idling and the voltage slowly starts to drop slightly to 400mV and the engine starts to idle roughly - this will be because the ECU sees a slightly lower than 450mV signal as a lean signal and starts richening the mixture, because the sensor doesn't respond properly it just continues to richen the mixture further and further until its idling very rich and starts to become quite rough.

It's not until I actually drive the car for about a minute that the O2 sensor warms up from exhaust gas. So I was right all along that starting cold and letting it idle for a long time without driving is bad for it with the current dodgy oxygen sensor. If I start it and drive off straight away the exhaust gas warms it up quickly enough to not cause problems, as long as I keep up a decent pace.

Once the O2 sensor is warmed up by the exhaust it does work properly however as soon as you drop back to coasting down hill, slow cruising or extended idling the amplitude of the signal quickly starts dropping away to less than half of what it should be. Because a partially warmed up O2 sensor outputs a lower than normal voltage for a given mixture that means it falsely biases the signal towards lean so the ECU causes the engine to run over-rich when the O2 sensor is only partially warmed up. So it definitely needs replacing.

The second thing I discovered is that it looks like I may still have intermittent lean under WOT at low RPM. Whether that has been re-introduced by the swapped injectors or reconnection of the canister purge line I'm not sure at the moment.

It's something I've seen from time to time on the Lexia but its far more obvious watching a waveform on a scope. A petrol engine should run rich (flat-line 800-900mV O2 sensor voltage) under WOT, and above about 2500, 3000 RPM it is. However if I accelerate with a wide throttle under 2500 and especially under 2000 rpm the O2 reading often goes lean and flat lines there for several seconds at a time.

More importantly when I feel and hear the performance "sag" (as the torque converter is locking up, loading the engine) it does so at the exact moment that the mixture swings lean, then when it "recovers" a few seconds later and starts picking up again the O2 reading swings rich again, where it should have been the whole time.

I don't think its an upstream exhaust leak otherwise it would read really lean all the time (and wouldn't affect the performance in open loop anyway!) so it can only be one of two things: a) A misfire that causes a "false lean" reading by spewing un-burnt oxygen into the exhaust, or an actual lean condition due to a fuelling problem. (A vacuum leak wouldn't normally cause a problem at WOT as there is no vacuum)

I don't know any easy way to tell if its a misfire causing a false lean reading or not, (other than hooking the tailpipe up to a 5 gas analyser while the engine is under load...) so given everything that has been double checked to try to eliminate misfires I'll just have to assume its not a misfire causing a false reading.

Which brings me back around to fuel pressure once more. Today I decided to go for a drive with a volt meter connected to the fuel pump connector as well as the O2 reading on the scope. Quite an eye opener. For a start, given that the battery voltage is over 14 volts the highest I ever saw the voltage on the fuel pump was 13.3 volts when I first set off.

After driving for a while the voltage dropped and dropped. At various times I saw it get as low as 12.6 volts! Then it would gradually creep its way up to 13.1 volts or so for no apparent reason. During this time the headlights were off, rear window demister off, the cabin fan was on a very low setting (the voltage dropped even lower with that on) and I was moving fast enough to avoid the cooling fans coming on. (They only come on when I slow down)

When I got home and checked at idle the fuel pump was at 12.9 volts and the battery terminal voltage 14.05 volts, so 1.15 volts lost at the time of the measurement, possibly more when it was getting down to 12.6 during driving. Not good! On the other hand I couldn't see a concrete correlation between the battery voltage and the performance during the test drive.

I stopped and did the usual battery off reset part way and it didn't really make much difference. I was fairly low on fuel so I filled up before going home - as soon as I drove off the forecourt I could feel the car was more responsive - the lean episodes under WOT at low RPM were still occasionally present but they were not as severe or long lasting and the performance at high RPM was very noticeably better. Hmm...

I wish I had some way to monitor fuel rail pressure while driving as something odd is definitely happening under WOT below 2500 rpm, and it comes and goes, sometimes its responsive there (rich reading on the O2) and sometimes it really sags and goes flat (lean reading on the O2) for no reason that I can see.

Above 3000 RPM under WOT it stays rich, I can't really understand how a restricted fuel delivery could make it run lean at low RPM under WOT but not high RPM - doesn't make sense. Either that or one of the inputs (MAP/TPS etc) is causing a lean mixture to be calculated in open loop mode, or possibly the canister purge solenoid is only opening at low RPM and not high RPM ? I really need to blank that off again now that I can monitor the O2 sensor...

None of these symptoms are new with the new injectors - these exact symptoms have come and gone intermittently for a long time, I remember spotting intermittent lean O2 reading under WOT at low RPM more than a year ago, and I'm sure this must be a critical piece of information, given that the sag in performance and recovery correspond precisely with the O2 reading...

[lexi]

Today I decided to go for a drive with a volt meter connected to the fuel pump

Mmm.............sounds like Aspergers

Police stopped a suspicious looking driver in Coatbridge today. Thinking he was using a phone they discovered a device attached to his petrol tank.
The man, from New Zealand, said he was" doing some testing". A police spokesman said that other electrical devices, computer files and rolls of gaffer tape were found in the boot of his car, along with six incendiary devices and a gallon of petrol. When asked if they were for Molotov Cocktails, he said that they were for "testing purposes". A statement has been sent to Mrs Mandrake.

[Mandrake]

Thanks Alex, I needed a good laugh today