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

[Mandrake]

There's your problem - someone has stuffed rags into the intake runners. No wonder it runs like crap.

Re the fuel supply - provided your infeed pressure remained at or around 3 bar, I would not be too concerned for an idle test with the low return rate. A dyno would show you leaning out if this is the problem.

But don't forget that I AM seeing a lean condition under wide throttle under load <3000 rpm as reported by the Oxygen sensor, that's why I went chasing the fuel rail pressure and fuel pump delivery in the first place.

I have not re-tested for a lean condition since changing the fuel pressure regulator, but I will soon.

Lean under wide throttle won't be a vacuum leak, its either going to be low fuel pressure (seems ok, but I can't test it under full throttle load) or an injector problem, (injectors tested identically balanced last time I checked) or insufficient injector opening time due to an ECU/wiring fault or an input sensor signal fault to the ECU.

One question that I can't find the answer to anywhere, is that if I have a single cylinder misfire under load, will the oxygen sensor read false lean due to un-burnt oxygen (and fuel) from one cylinder ? I believe it will, but I can't find a definitive answer on this.

If its true my "lean condition" could actually just be a single cylinder misfire under load - exactly what I thought I had and fixed months ago...

The consistent flaw in much of your experimenting, is you're testing at situations of negligible load, for problems that start to occur under load with an engine up to temperature.

That's not entirely true. I've tested as much as I can under load. Anything that I've replaced (such as map sensor, coil pack, spark plug leads, spark plugs etc) has by definition been tested "under load".

Things that I have not been able to test under (driving) load include fuel pressure, actual spark voltage to the plugs, checking for misfire under heavy load etc, and I really don't have any way to do that.

The lack of performance I'm seeing at the moment is actually worst when the engine is cold and starts to go away after a few minutes, although it still isn't great when warmed up.

The major problem is that the symptoms are just not consistent, they're all over the place, hour to hour, day to day even if I don't touch anything, as if there are are multiple intermittent faults, so isolating and identifying them is proving extremely difficult. I never know whether the change in symptoms is due to something I did or whether it would have done it by itself anyway.

[Mandrake]

Went out for a test drive tonight with the Lexia to try to get a handle on what is going on but have come back home frustrated, fed up and out of ideas...

It's far worse since I changed the fuel pressure regulator, despite the fuel pressure of the new regulator reading higher at 2.9 bars, and being absolutely rock steady when snapping the throttle open. (with the vacuum pipe off) As far as I can tell the pressure regulator is working perfectly but its got all the performance of a horse with a broken leg now!

It feels like it has a severe case of fuel starvation, or is running on only 4 or 5 cylinders, that's how bad the power loss is, its performing worse than my 2 litre 4 cylinder used to. With wide throttle below 2000 rpm the oxygen sensor is indicating lean as well, although that is the ONLY thing I can see on the Lexia that is amis, everything else including all sensor data looks perfectly ok.

I cant hear or feel the roughness normally associated with a misfire when driving, it seems to be smooth but gutless, however when idling it misses every one to two seconds like an injector pulse or spark went missing...(it has been doing that at idle before I changed the regulator too)

I am at a complete loss what to do now. It's a lot of work to put the old fuel pressure regulator back in, particularly when I don't know whether the original, or replacement, or both are faulty, and its expensive to replace it with a new one.

Quite possibly its not the pressure regulator to blame but something has been disturbed during the job, as usual, as it seems to be impossible to work on one part of the engine without disturbing other parts of it... The manifold gasket I fitted was a second hand one in good condition that wasn't on the car for long, and a vacuum leak wouldn't affect full throttle performance anyway, right ?

Does anyone know a GOOD garage in the Glasgow area with proper engine diagnostic equipment (scopes etc) who might be able to have a look at this problem for me without ripping me off blind - the loss in performance now is very obvious not subtle, and quite frankly at the rate I'm going I'm NEVER going to get to the bottom of this engine performance issue, I'm way out of my depth, have nowhere proper to work on the car and I'm just plain fed up.

Either that or does anyone want to take the car off my hands ? Seriously. I'm not getting any enjoyment out of driving a car that just isn't running properly, and I'm sure someone smarter than me with more experience fixing engines can get to the bottom of it.

At least the gearbox seems to be working well since changing the oil and adding the lubegard, that much was successful...! No funny noises, no slipping, gear changes are nice and smooth, nothing to complain about there. Just p**s poor performance from the engine!

[Northern_Mike]

You have replaced that knackered old battery clamp haven't you? I've had numerous motors, from a Renault 18 up to an MX5 and Activa that have acted most oddly when the battery has either been dying or the connections have been iffy (even though they appear tight)..

I think a joint FCF effort is needed to put you, and it , out of your misery and get it sorted once and for all.. any takers?

[Mandrake]

No I haven't replaced the battery clamp yet Mike, its true that I noticed the split clamp the same day I did the fuel pressure regulator, just as I was finishing up after that job I couldn't get it to clamp properly and discovered it had split, probably I finished it off by trying to over tighten it when it was too worn to clamp without closing right up...

I did also notice the Lexia was only reporting 12.3 volts measured by the engine ECU while the engine was running which seems a bit low, but I don't know how accurate the voltage reading from the ECU is or whether its low enough to cause an issue. I'll need to get my multi-meter onto the battery clamps and compare it to the battery posts. I'll get a couple of those clamps from Halfords, but the pessimist in me thinks this is just yet another new problem and not part of the ongoing intermittent engine performance.

I really am reaching the end of the road with this car, I should have listened to you a few pages back... I'm talking seriously with the other half tonight about selling it, so if anyone does want a challenge let me know... Only problem is the MOT is due in August, I was planning to take it on July 20th (earliest date I can) to give maximum time to attend to any issues, but now its running this badly I'm not sure if it will pass the emissions test. Until swapping the fuel regulator last weekend I felt that it probably would have passed with a couple of minor advisories.

[Northern_Mike]

No I haven't replaced the battery clamp yet Mike, its true that I noticed the split clamp the same day I did the fuel pressure regulator, just as I was finishing up after that job I couldn't get it to clamp properly and discovered it had split, probably I finished it off by trying to over tighten it when it was too worn to clamp without closing right up...

I did also notice the Lexia was only reporting 12.3 volts measured by the engine ECU while the engine was running which seems a bit low, but I don't know how accurate the voltage reading from the ECU is or whether its low enough to cause an issue. I'll need to get my multi-meter onto the battery clamps and compare it to the battery posts. I'll get a couple of those clamps from Halfords, but the pessimist in me thinks this is just yet another new problem and not part of the ongoing intermittent engine performance.

I really am reaching the end of the road with this car, I should have listened to you a few pages back.

That is not always the most sensible option. I say replace the battery clamp BEFORE you do anything else, wait, take it for a MOT, and take it from there.. you have put an inordinate amount of work into it, and it's not going to be worth a lot with very short MOT and a mystery running issue. At the very least, you'll have a fail sheet you can wave at prospective buyers..

[Hell Razor5543]

It is also possible that a competent MoT tester might pick up on something that has (so far) escaped your notice.

[Northern_Mike]

It is also possible that a competent MoT tester might pick up on something that has (so far) escaped your notice.

There is that, but I suspect it a)needs a battery clamp. and b)is something and nothing, but needs a fresh pair of hands and eyes to look at it. There's little Simon hasn't checked, so it can't be anything serious..

[addo]

Following from the clamps I would be looking at a loan of "known good" ECU.

If still no change, buzz out every engine harness wire from sensor plug to ECU. Failing a result there, just for giggles I'd gut the cat.

[Mandrake]

I will change the battery clamps and check for any voltage drop.

Would trying a known good engine ECU not require also swapping over the texton, eg a dash out job ? Not too keen on that...

I haven't continuity checked all of the ECU wiring, but quite a few of the sensor lines I have checked including the knock sensor wiring.

[addo]

I believe it'll work with your current Texton box if you have the loan keychip as well.

FWIW Texton swapping requires glove box and passenger airbag removal. No more than that.

[Mandrake]

To the best of my knowledge the engine ECU and Texton are keyed together at the factory and can't be reprogrammed to work with any other already programmed box.

Brand new replacement texton or engine ECU's can be programmed only ONCE to match an existing partner ECU using a Lexia. So swapping in a second hand engine ECU would require the matching texton and key transponder as well.

[addo]

All you need from the key is the chip, you don't need the aerial. If you were really concerned you could always borrow the Texton box as well - but I remain unconvinced it's needed.

From what I've read about ECU unlocking, the chip has a 16-character hex code of which I understand the last four are the "unlock code" we use with Lexia. The entire string is fed to the engine ECU via the Texton box - I believe it only powers the aerial up to read the code, then sends the result down the line.

I'm very tempted to try a spare unit with my keys and ECU to see if it works - suspect it will.

[CitroJim]

Does anyone know a GOOD garage

Simon, the chances of finding any garage that could deal with this are zero. They don't exist in the UK. End of...

You have replaced that knackered old battery clamp haven't you? I've had numerous motors, from a Renault 18 up to an MX5 and Activa that have acted most oddly when the battery has either been dying or the connections have been iffy (even though they appear tight)..

I think a joint FCF effort is needed to put you, and it , out of your misery and get it sorted once and for all.. any takers?

Agreed on all points Mike...

Simon, don't give up just yet. I understand how frustrated you are but walk away from it for a few days and then return with fresh vigour..

You also need someone else to look too. Fancy a trip down south at some point to see Team WFA?

[addo]

Is the UK really that bereft of ability?

What about all the proper performance forums where people are semi-competitive? I know they all have a resident troll/d¡ckhead or two but often there are clued-in people who don't mind so much meeting someone halfway when they've demonstrably put in an effort. Even getting an amateur racer to pedal it would be a good start. I wouldn't hesitate to join a forum that specialised in some other marque if the people seemed to know their stuff; a mysterious problem (as it is perceived) will attract fixers of all stripes.

Also, put a "positive spin" budget cap on it, as in "I am going to diagnose and completely fix this for £XXX or less".

[CitroJim]

Is the UK really that bereft of ability?

In a word, yes

It's sad but that's how it is. Nobody is interested in really understanding how things work now and words like imagination, drive, ambition, determination and curiosity are dirty words in Britain today and have been for many years.

Obviously there are exceptions but they are few.

To be brilliant at anything in the UK is very much frowned upon. Mediocrity rules.

Raw nerve touched? You bet