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

[Mandrake]

Another update on the saga, and it's not good news, depending on how you look at it.

I'm fairly certain now that the ECU is not at fault, thanks to the loaner ECU from David - for the first few days the car ran nicely with the swapped ECU, however as sure as death and taxes it has now exhibited its typical intermittent poor running and misfiring symptoms with the substitute ECU still fitted.

On Saturday I spent time swapping ECU's back and forth while I was working out the ECU locking and key programming stuff, after having had the battery off and having swapped the ECU's a few times it was back to its mediocre performance symptoms again. I still had the hose to the charcoal canister purge solenoid blanked off so I've put that back to normal and noticed no real change - worse or better, so I think that may have been a red herring all along.

On Sunday we went for a drive, lots of urban stop start 30mph stuff, it started off ok but within minutes went down hill, very little low rpm grunt or pickup, and surging performance in the mid range. Flat as a pancake and felt like it was intermittently missing one maybe two cylinders worth of performance...then towards the end of the drive it intermittently seemed to run a lot better again, so even during one drive it was fluctuating from terrible to ok to terrible again.

On Monday the car wasn't started for the first time until about 2pm in the afternoon on a warm sunny 18 degree day, I started it from outside with the bonnet open so I could listen to how it started, it was clearly misfiring on at least one cylinder, possibly two at idle, with the engine visibly shaking and kicking.

Trying to snap the throttle quickly open only about 20% was causing a massive stumble to the point where it was completely cutting out for a half second before recovering. Any time the throttle was snapped quickly open from idle it was stumbling and cutting out then recovering. I tried to catch a video of the stumbling on my phone but by the time I started filming it the symptoms had abated to the point where it wasn't as obvious.

When checking the negative clamp was tight on the battery I found it wasn't as it suddenly turned, so I decided that I couldn't put off replacing them any more. I've fitted the quick fit types that RichardW had recommended as the other ones I had did not fit the wires at all. Getting all four positive wires into the clamp and clamped securely was challenging but it all worked out in the end:







The wires that I stripped back were all nice and clean and shiny - no corrosion at all.

Those of you who have been nagging me to replace the clamps will be happy to see it done, however rather predicatably it has made not one iota of improvement to the symptoms! The engine was still misfiring, running rough and stumbling when snapping the throttle after the new clamps were fitted. I never thought the battery clamps were to blame for the symptoms, but the old clamps were to the point where they had to be replaced, as even the positive one had started to split.

I gave up in disgust on Sunday because it was running so poorly, so blatantly misfiring, it had all the hallmarks of an ignition misfire despite every single item in the ignition system (including the ECU now) having been replaced or ruled out, and yet the misfire persists.

Then this morning the car was started at 8am in 9 degree weather and it started and ran perfectly, drove the 10 minutes to the train station with lots of grunt and very little in the way of symptoms except for a little bit of surging in the mid-range which truthfully could be torque converter related... However while the gearbox is certainly not in the greatest condition the symptoms I was seeing yesterday were all in neutral at idle or while trying to rev the engine in neutral, so can't be gearbox related.

It seems almost like the symptoms are temperature related - not coolant temperature, as on a cold morning its still running fine when the coolant is up to temperature, but maybe engine bay ambient temperature as it seems worst when the engine bay is warm on a warm day. If it's sat in the sun all day before being started it starts poorly, while it almost always runs well first thing on a cold morning.

Can anyone think of anything that could possibly cause such bad misfiring and stumbling on a warm day but the very next morning in the cold it runs nearly perfectly ?

I'm pretty much completely out of ideas again - I really would like to get a current clamp probe onto the injectors and ignition coil primaries as I'm suspicious of a injector coil problem such as a short developing when the winding heats up, but I'm not sure that I can justify the cost of buying a current clamp probe.

Something is causing it to intermitently misfire in a major way, but is it spark, fuel, or compression ? I still don't know, as all three have at various times been tested and ruled out, but obviously one of them is intermittent.

[Mandrake]

Hmm, what do people think about the possibility of one or more sticking/clogged injectors ?

http://www.aa1car.com/library/2003/ic30336.htm" onclick="window.open(this.href);return false;

The injectors need to be cleaned, if an engine is experiencing any of the classic symptoms of dirty injectors, such as lean misfire, rough idle, hesitation and stumbling on light acceleration, a loss of power, and higher hydrocarbon (HC) and carbon monoxide (CO) emissions.

Let's see, lean misfire ? Yes maybe, it would fit the symptoms of the timing getting retarded due to knocking. Definitely a misfire of some sort occurring. Rough idle ? Check. Hesitation and stumbling on light acceleration ? Check. Loss of power ? Check. High HC and CO emissions. Check. So high in fact that it nearly failed the emissions test.

Although I've done an injector balance test that passed that was nearly 12 months ago now, and a lot has changed since then...

The only thing that I'm not sure fits the symptoms is could sticking or clogged injectors be an intermittent fault that would vary from day to day ? That I'm not sure about.

In the mean time I could put some more injector cleaner in the petrol tank (I still have a dose worth left) and perhaps do another injector balance test, although this time on a hot symptomatic engine.

[isisalar]

A lexia session on my HDI showed up a duff injector, if that's any help.
Cheers
Paul

[Mandrake]

Sadly the Lexia never reports any fault codes for the engine even when its running like a complete dog!

[lexi]

What about Superloopy's V6 ? you will get something for current one from We buy your old jamjars.
Swop all yer good bits over . Sorry to hear about the ECU not sorting it after your work and hassle.

[addo]

Nice work on the battery clamps.

If there's no faults showing with either ECU, there is either a supply fault (fluctuating feed pressure or voltage/current), or a waste problem.

Upon encountering the stumbles, I would disconnect the radiator fans without stopping the motor, and see if the problem goes or reduces. I would also look at MAP readings while the engine is misbehaving, especially when its struggling to make progress up a hill.

Checking the alternator output would be really useful, it is a mongrel to access but if there's a heat driven failure occurring this might be necessary.

[larppaxyz]

Hmm.. maybe we should try to only reset gearbox control unit and see if that helps (like resetting ECU does). I have same gearbox issues like Mandrake (but as mentioned before, when engine works, gearbox works).

[Mandrake]

Hmm.. maybe we should try to only reset gearbox control unit and see if that helps (like resetting ECU does). I have same gearbox issues like Mandrake (but as mentioned before, when engine works, gearbox works).

I tried an auto adaptive reset on Sunday when it was running poorly - no improvement.

If anything doing a reset on the gearbox ECU while the engine is performing poorly makes gear shifts and gearbox behaviour worse, probably because the gearbox ECU learns from bad data. As you say, when the engine performs well the gearbox works smoothly too, so I think the gearbox misbehaviour and poor shift quality is an effect not a cause.

Again this morning on a cold morning the car started and ran well with lots of power, the only noticeable issue is the persistent hesitation when accelerating quickly from idle.

[Mandrake]

Nice work on the battery clamps.

Not the ideal type of clamp but they do seem to grip very tight and are quick and easy to disconnect or reconnect which is handy for troubleshooting.

If there's no faults showing with either ECU, there is either a supply fault (fluctuating feed pressure or voltage/current), or a waste problem.

Fluctuating feed pressure ? Do you mean fuel pressure ?

Waste problem ? Not sure what you mean by that.

Upon encountering the stumbles, I would disconnect the radiator fans without stopping the motor, and see if the problem goes or reduces.

I can't see how the radiator fans could cause this. They're not running at the time when the stumbling occurs. The stumble occurs when flicking the throttle open a bit from idle. Every time.

I've even tried moving and wiggling the ECU wiring harness at various places and testing a throttle flick, but nothing makes any difference. Although the performance and misfiring seems to vary from day to day this stumble when flicking the throttle open seems to be there permanently now, and has been for a few weeks at least.

If I can find the cause of this it may shed light on the main performance issues, as a stumble when flicking the throttle open is almost certainly a misfire ? Either an ignition misfire or a lean misfire ?

I'm not even snapping it wide open - just flicking it open quickly to about 20% is enough to make it stumble badly and drop down in rpm for maybe half a second or so.

I would also look at MAP readings while the engine is misbehaving, especially when its struggling to make progress up a hill.

You've suggested this before but I can't really make heads or tails of the MAP reading while driving... at lower rpm <2500 where the lack of power is most obvious I tend to notice that the map reading reaches its maximum (atmospheric) with a relatively low throttle opening of around 40% or so, but for all I know that could be normal at low rpm.

Checking the alternator output would be really useful, it is a mongrel to access but if there's a heat driven failure occurring this might be necessary.

I agree checking the alternator output for spikes and noise needs doing, it does look to be a pain to get at though.

[addo]

MAP readings with the throttle partly or fully open, will reflect the engine load. Would you consider plumbing in the spare oxygen sensor bung and refitting that backpressure gauge?

I think it's safe to rule out fuel supply, unless you want a decoupler and cabin gauge for verifying this.

The fans - are you not using AC during any of the stumbles? A fan motor that's physically sticky will draw excess current as it starts up each cycle; this is like briefly switching off power to the ECU. S2 fans don't seem to have the same problem as S1; it's more a physical bind than carbon brush wear.

[Mandrake]

MAP readings with the throttle partly or fully open, will reflect the engine load. Would you consider plumbing in the spare oxygen sensor bung and refitting that backpressure gauge?

I'm not willing to do that just at the moment, no. It's a lot of hassle for something I'm pretty certain to not be the problem, especially as we're rapidly moving into winter now.

The fans - are you not using AC during any of the stumbles? A fan motor that's physically sticky will draw excess current as it starts up each cycle; this is like briefly switching off power to the ECU. S2 fans don't seem to have the same problem as S1; it's more a physical bind than carbon brush wear.

A/C and radiator fans are off during the stumbles I've been describing. I don't generally use the A/C unless its either very hot (no chance of that now) or the window needs demisting. Certainly when the car is parked and idling while I'm working under the bonnet I never leave the A/C running.

I'm standing under the bonnet flicking the throttle open slightly and its stumbling badly as I flick the throttle, no radiator fans or A/C running. I notice that the severity of the stumble varies as the engine warms up and/or day to day, sometimes its really bad as in completely cutting out for a fraction of a second, sometimes its minor, but it's always there so I think tracking down this stumble may actually lead me in the direction of the problem that is also affecting overall performance, and as its a far more easily and consistently reproducible problem it avoids the whole trying to judge the performance during a test drive, which is very subjective. (after a long time of it running poorly you start to forget how well it should be running...even trying to judge performance on a 1-100 scale starts to become impossible)

I've also realised that this stumble is also very likely the cause of the surging idle issue that this car (and larppaxyz's) intermittently has - sometimes when starting hot or after returning to idle from driving the rpm will dip down below idle speed perilously close to stalling, surge well above normal idle, drop down low and try to stall, surge above etc, often 3 or 4 times in a row until it gets a hold on the situation.

What might be happening is this - after starting or dropping back to idle the ECU tries to stabilise the rpm with the ICV, if the rpm drops below idle it quickly opens it to prevent a stall. Normally this would result in a quick and smooth recovery of rpm and it settling on the correct speed. However due to this stumble issue when it dips below idle and the ICV is quickly opened the engine stumbles (misfires?) causing the rpm to drop even lower, the ECU opens the ICV even more, and it comes close to stalling before the engine recovers, the rpm then surges above normal because the ICV has been opened so wide to try to prevent a stall. Fix the stumble and I'm almost certain this surging idle will be gone too.

The problems I'm having are 100% not the ECU - Thursday was a very wet day with heavy rain and high humidity, and the car was running like an absolute pile of crap right from first starting. When trying to accelerate you could feel it really struggling and constantly "tugging" backwards and forwards like someone had a rope hitched to the back and kept yanking on it. Surely that's got to be a massive intermittent misfire ?

The car made 6 trips on Thursday through torrential rain, two 10 minute trips and four 20 minute trips. In every case it ran like crap for the first few minutes with the tugging as described above, after maybe 20 minutes of driving the symptoms eased somewhat but didn't completely subside. As soon as the car had been left to sit for a couple of hours the symptoms came back again. The next day with the rain gone the tugging effect was gone.

Has to be misfiring doesn't it ? If I didn't know any better I would think that misfiring in wet raining conditions would surely be spark related ? What else would cause misfiring to get much worse in damp conditions ? Under the bonnet would have been very damp to begin with and would have dried out somewhat after 20 minutes driving.

A stumble when snapping the throttle quickly could definitely be caused by a weak spark misfire, but could a fuel problem like a slightly blocked injector also lead to it misfiring when snapping the throttle, or is that less likely ?

I'm so sure that I have a spark or fuel related misfire as the root cause of all my engine problems but I just don't know how to narrow it down and prove conclusively what's causing it, at least not with the amount of diagnostic gear I have.

If its spark I don't understand how, when the entire ignition system has been replaced! And yet the symptoms fit weak spark or lead insulation breakdown to a T...

In the fuel system the injectors are the only thing that has not been replaced...

[dnsey]

OK, if it seems ambient temperature related, that might help in narrowing things down.
How about pointing a heat gun at potential suspect components and noting the effect?

[Mandrake]

The plot thickens! Today is fairly dry, when we were out in the car this morning it wasn't misfiring badly enough to feel like it was "tugging" like Thursday, but power was well down, and somewhat typical of late.

The worsening misfire with humid heavy rain conditions and some of the other symptoms kept nagging on my mind so this afternoon I tried something on a hunch.

I took out the second hand coil pack I got from KP's breaker and refitted the new coil pack I bought last year which I had removed on suspicion of being faulty.

I didn't disconnect the battery, I didn't touch anything except removing the top plastic cover on the engine, disconnecting the spark plug leads and primary connector from the coil pack, swapping the coil pack, (transferring the spark plug boots from one coil pack to the other and keeping them on the same cylinders) and putting things back. I was careful not to disturb anything else. I then went for a drive.

Blow me down if the car wasn't going like a rocket. The change was massive and immediate. The performance at higher rpm was immediately back to what it should be, although pickup at low rpm was still down a bit on what it should be. After about 5-10 of mixed driving the low rpm pickup had started to return as well. (My guess is it took time for the ECU to advance the timing map again after previous misfiring)

Because the coil pack I took out was very hot and was replaced with a cold coil pack going into an already warmed up engine I drove the car for around 30 minutes to warm the coil pack up just in case the one I put in was symptomatic when hot but not cold - but there was no deterioration in performance, instead it got better.

Clearly the misfire is ignition/spark related then! I didn't touch anything remotely related to fuelling, and there was only about half an hour between the poor running on the old coil pack and the excellent running on the new coil pack.

Here's the thing though, I don't think any of my coil packs are faulty!!

For those who have lost track, I have three coil packs - my original one that came with the car which I kept after I replaced it, a new one that I bought from ebay and fitted around October last year, and a second hand one I bought from KP a few months ago which has been in the car since then.

The reason why I say that I don't believe ANY of them are faulty is because several months ago I had the NEW coil pack in the car and it was misfiring and performing just as poorly as it has been recently, and at that time putting the ORIGINAL coil pack back in the car restored almost normal performance! For that reason I believed the new coil pack had failed. A few weeks later it was running poorly again and the chance to pick up a second hand coil pack from KP occurred, I changed my ORIGINAL coil pack for the one from KP and once again the performance was immediately improved, for a few weeks anyway...

Now exactly the same thing has happened - really poor performance with KP's coil, re-fit the new one from last year which I'd previously written off as faulty and the performance seems almost perfect!

So what's happening then ? I believe that the act of swapping the coil pack is physically disturbing the actual fault - and I believe that the faulty item is most likely the spark plug leads...despite them having been replaced last year!

Those with long memories will remember that I've changed the spark plug leads twice. The originals were definitely faulty with two intermittently open circuit leads confirmed with a multimeter. When I fitted the first replacements I damaged one of the leads and put a tiny puncture in one of the leads where they go through the plastic support clips near the coil pack. This was enough for the spark to jump through the hole to the tappet cover and cause a misfire.

Almost exactly a year ago the day before I paid a visit to David Hallworth I taped up the puncture hole with 3M self amalgamating tape and the car instantly started running like a rocket and ran flawlessly for two weeks before it started misfiring again. When it started misfiring again I checked the lead and the spark had actually melted/burnt a hole through the tape at the site of the puncture! At the time I felt that was conclusive evidence that the damaged plug lead insulation was the problem, I taped it up again and once again it started running normally, although this time only for a few days.

I promptly ordered a second set of leads and fitted them - and much to my disappointment fitting the new leads didn't restore normal performance like the tape around the old leads did....so I assumed that something else had gone wrong, and never suspected the leads again as they were new so "must" be ok. It's never really been back to 100% performance since then for any length of time.

All the recent symptoms point towards a secondary ignition fault - intermittent misfire that gets much worse when the weather is wet and damp, and better when the weather is dry, a misfire that gets much worse under open throttle load (low spark voltage or an insulation breakdown giving an alternative path for it to jump to will do this) so is it somehow possible that I've been unlucky and ended up with a dud set of spark plug leads that have had an insulation fault since new ?

One spot that I'm suspicious of is where the right hand plug lead goes under the back of the plastic top cover - one of the curved plastic pieces pushes down directly on that wire and in fact digs into it if the top two screws on the plastic cover are tightened. Even though there is a conduit sleeve to protect the wire there there is a serious kink in the wire now. Where that wire is kinked and pressed down by the top cover its also directly above the right hand earth wire and pressed hard down onto the earth wire lug - so if there was any insulation breakdown at this point it has a very short path to jump to earth.

The top/rear two screws for the top cover on my engine are pretty badly stripped, in the past I've put a bit of copper wire down the holes etc to get them to bite and tighten down properly, however today I just left them loose - which means the top edge of the cover is not pushing down tightly on the spark plug wires like it normally does. Co-incidence that it runs well now ? I don't think so...

What do people think ? If changing the coil pack fixes the symptoms temporarily but none of the coil packs are seemingly faulty (since they've all had turns at being "good" and "bad" at various times) could it just be that I'm disturbing damaged plug leads ?

I really do have half a mind to just go and replace those plug leads again.... And see if I can do something to protect the wires better where they come out under the top cover as the right hand one really does get pinched badly under the cover. (But seems to be designed that way...) Should I trust my gut and replace the leads or should I investigate the wiring where it runs under the cover a bit more closely first ?

Oh and by the way, the gear changes are lovely and smooth again now that the engine is running properly, it took maybe 5-10 minutes of driving after the coil pack swap with the gearbox seeming a bit "confused" but after that it settled down nicely. So it really does seem that a misfiring engine does terrible things for the operation of the gearbox...

[lexi]

should I investigate the wiring where it runs under the cover a bit more closely first ?

This first.^^^

Pinch the leads back in and try to replicate the suspected short.......Make and break looking carefully what you are moving. I know I have mentioned it before but darkness is your friend for those shorts.
Were they nice Bougicord leads? Could be a bruised lead......maybe. Would an alternator spike give any ecu issue?........just thinking aloud.

Have you tried pulling a plug lead when issues arise>? Not easy I know but could give indication if one makes a difference,or not

[addo]

If you are certain it's the coils, I would suggest you "break" a coil pack, and mount the coils remotely, with flying leads to all plugs - not crimped into a channel.