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

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

Post by Mandrake »

Unplugging the oxygen sensor is what I'll try next then. If the weather is ok tomorrow I'll try it then. I think I saw where it is when I was doing the handbrake cables - on the left hand side of the pipe from the cat to the exhaust manifold about half way up ? Is the connector nearby or some distance of cable away from where the sensor actually is ? I assume its an up on ramps job to access the connector from below...or perhaps from the top if I remove the air filter ? (Mind you I'd rather unplug it without disturbing the air intake pipes if possible so as not to confuse the situation by accidentally introducing air leaks...)

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

Post by CitroJim »

Simon, you should be able to get ton the connector by reaching down behind the engine in the vicinity of the throttle body near the bulkhead. In fact if you look carefully you should see the sensor poking out of the side of the cat on the nearside and thus be able to follow it's wiring back to the connector.

Normally, if the oxygen sensor is original it'll have it's wires sheathed in blue systoflex terminating in a brown 4-pin plug going into a black free socket with a red pull-bar on it. Pull out the red bar to unlock the plug from it.

You should be able to see the connector and separate it without needing to strip anything else away.

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

Post by Mandrake »

Thanks Jim, sounds quite easy to get to, I guess I might have to tie the plug in place to stop the cable falling back against the exhaust ?

I've been doing quite a lot of reading at the lambda power website and I'm fairly convinced now that it fits the symptoms. In particular on this page:

http://www.lambdapower.co.uk/Diagnosis/ ... _index.asp" onclick="window.open(this.href);return false;

Point 4 fits my symptoms exactly while causing at 1500 rpm with a moderate but steady throttle - in these conditions the ECU can be alternating between open and closed loop, normally you wouldn't notice but the sensor fault could cause the mixture to be normal in open loop and lean in closed loop hence the hesitation and surging which does follow a cycle every second or two.

Likewise point 5 - although idle is steady, just slightly above idle (anywhere between 1000-2000) cycles up and down as described. (I notice the ECU input data on the Lexia has idle, mid throttle, and wide throttle sensor input from the pedal, it transitions from idle to mid throttle with just the slightest depression of the accelerator, I'm assuming that the fuelling strategy is different between the idle/mid throttle modes, causing the hunting of engine revs not to occur until there is a slight throttle opening putting it into the "mid throttle" band)

Finally in their case studies:

http://www.lambdapower.co.uk/CaseStudies/Case_index.asp" onclick="window.open(this.href);return false;

The 1996-N Fiat Cinqucento 1.1 symptoms sound very similar - leaning mixture under steady driving conditions leading to misfiring, but with no apparent problem with idling. They identified this by measuring the injector on-time during a test drive under cruising conditions. Unfortunately I can't try this as I don't have a co-driver to drive while I watch the laptop! :lol:

Interesting reading actually, it looks like even dealerships misdiagnose lambda problems quite often due to the inability of most older ECU's to detect and log lambda faults unless the sensor is totally dead, and possibly a lack of understanding of how lambda sensors work and an over reliance on fault codes as gospel :roll: ("The ECU says the lambda sensor is fine so it must be fine...")

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

Post by Mandrake »

Just a quick update, I'm running the car with the oxygen sensor disconnected for a few days to evaluate the change, so far there does seem to be quite a big improvement in the low to medium throttle performance, its far less hesitant and stuttery, and the throttle is much more responsive, in fact I'd go so far as to say it is rather zippy now with almost no hesitation, and the idle is smoother as well. The odd cycling of engine revs at 1500 while stationary, and 2300 rpm cruising at 60mph is gone too. Not perfect by any means, but I wouldn't expect it to be with no oxygen sensor as the ECU is having to "guess" the fuelling without any feedback loop.

No oxygen sensor may be better than one that gives false data, but a properly working oxygen sensor should be better again. No engine management light with it disconnected, but the Lexia does report the oxygen sensor is faulty and I can see that oxygen sensor status is 0 instead of 1 even at idle meaning that it is ignoring it completely. (1 being closed loop operation, 0 being open loop)

The engine is still labouring and struggling a bit under 1500rpm in some circumstances (although it picks up quicker and pulls away now) and I do still hear an intermittent noise that sounds like a vibrating/grinding noise when it labours below 1500rpm, but I have another lead that I am following up regarding that which I will elaborate on if it pans out...if I'm right there is no one individual problem causing all the symptoms, its a combination of 2 or 3 things which are compounding on top of each other, one possibly being worn engine mounts allowing something to touch when the engine torques.

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

Post by RichardW »

Getting there Simon!

When you get the grumbling try just pulling the handbrake on a little - these are known for the brake calipers rattling at low engine speeds. There is (or was ) a mod available from Citroen which is a spring that bolts on underneath the caliper to put some pre0load on it and stop it rattling. Not cheap though at around £50....

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

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RichardW wrote: When you get the grumbling try just pulling the handbrake on a little
Good thinking Richard :-D I've just taken mine out of hibernation for a bit of use. Not moved a wheel in a couple of weeks at least and it is grumbling in the manner described that goes with gentle handbrake application. Interestingly mine does have the caliper mod.

In the next few days I'll pop the front wheels off and have a quick look at the pads although after a run of about five miles it's largely gone.

Simon, interesting results from disconnecting the oxygen sensor. A new one will be worth a try. You don't need to spend a huge amount on a genuine one as generic plugless ones are available at a reasonable cost. You just need to chop wires and crimp your old plug onto the new one.

Typical example of one I've just bought for my XM...

Ignore what it says about compatible vehicles :wink:

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

Post by xantia_v6 »

I would not jump to any conclusion that the oxygen sensor is faulty if there is still any sign that there is a misfire or that the engine does not have full power when running open-loop with the sensor disconnected.

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

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xantia_v6 wrote:I would not jump to any conclusion that the oxygen sensor is faulty if there is still any sign that there is a misfire or that the engine does not have full power when running open-loop with the sensor disconnected.
I quite agree. Have you had the inlet manifold off yet Simon, and checked the rear plugs and so on?

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

Post by Mandrake »

This forum is desperately in need of multi-quote :lol:

Richard: I tried the handbrake tonight but it had no effect on the groaning/shuddering noise, so I don't think its the brakes.

Yesterday I had a look at the heat shield above the cat and discovered that I'd refitted it wrong after doing the handbrake cables - the front section under the cat should tuck underneath the lip of the rear section tightly but it was sitting on top instead - when tapping under the car with a block of wood looking for anything loose that section was buzzing quite badly, now its silent when tapping, so that may have been some additional rattle when the engine was under load, but the basic noise is still there.

Jim: I know its not something I really want to be thinking about, but is there anything that could be wrong with the gearbox that could be causing a groan which passes right through the body as a vibration when under load at low revs ? Malfunctioning clutch or brakes in the gearbox maybe ? Low oil ? Anything at all ? The shifting pattern especially at low revs is sometimes a bit erratic and inconsistent, as if it can't decide what to do, and quality of gear changes is not that great sometimes with significant snatching on some occasions and times where it changes gear then changes its mind and goes back again. Despite all its auto-adaptive trickery it's nowhere near as smooth or consistent as the fully mechanical 4HP14 on my old 2 litre which was pretty much flawless. I'd previously put it down to age (14 years old vs 8 years when I bought my previous Xantia) but maybe there is a problem. I think its time I checked the gearbox oil level and colour, fortunately I think mine has the dipstick :)

I think part of the problem could be that sometimes at low speeds in 2nd and 3rd in the 1000-1500rpm range the gearbox is staying in full lockup thus causing the engine to labour at low revs where it can't develop enough torque, instead of entering limited slip or full torque converter mode, which would allow the engine revs to lift a bit and develop more torque. SOMETIMES it will do this and the car picks up nicely with no labouring, as the revs can rise to 1500rpm or so without needing to change down, other times its clearly in full lockup and the engine revs are held down and the engine struggles, especially on a hill. I've been reading through the 4HP20 training manual last night and its my understanding that it shouldn't be trying to maintain full lock up at such low revs when the engine is under significant load...could the groan even be limited slip trying to engage but failing ? The shifting and lockup control tables are VERY complex, so I may not have understood them quite right, I'll give it another read.

xantia_v6: It's too early to be sure, I've only been for one drive with the oxygen sensor disconnected where the car had time to get up to full temperature, but it does seem to have cured the misfire. During the week I only drive a short distance to work in a 30mph environment and the car is not up to full temperature before I get there. Having said that it was a chilly morning this morning and the car absolutely flew up a hill with a modest throttle in a way that it hasn't done for a long time, perhaps not even since I've had the car.

It still needs more evaluation, as far as I can tell theres no misfiring above 1500rpm, it is still struggling a wee bit under 1500rpm (not necessarily a misfire, hard to tell with all the other noise that is occurring) but I'm not sure whether the gearbox should be letting the revs get that low under heavy load while still in lock up in the first place, so the engine may have legitimate cause for complaint. If it was a manual I certainly wouldn't be labouring it up a hill at half throttle at 1200rpm in 3rd the way the auto box often wants to! As for whether there is full power - as I've said before I haven't driven another V6 so I don't know what level of performance "full power" might be. :twisted:

Jim: No I haven't done the rear plugs yet, its going to be a few weeks before I could get a chance to do that and I'm not keen on doing them by myself in a car park. :? I will get some plugs and a gasket ordered though. Any recommendations on sourcing the gasket ? Citroen ? GSF ? Pattern parts ? Ebay ?

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

Post by CitroJim »

The gasket, as far as I know Simon, is only available from a dealer. I gave the part number earlier. They only cost a couple of quid or thereabouts.

I'm sure the gearbox is OK but an oil level check would be good. What I do know though from experience, is that if the engine is not running correctly then the gearbox will become upset and not behave as expected. The auto-adaptives depend upon the requisite power being available from the engine and if it isn't then it won't work properly. In short, a duff engine can make the gearbox look duff too.

Early auto-adaptives like the HP20 are never as smooth as a late hydro-mechanical like the HP14 or 18. I note that when driving my V6 and XM. The difference is quite pronounced. Again, auto-adaptives only give their best when the engine is running properly.

There's nothing in the gearbox that can cause a groaning noise as far as I know. A dying HP20 tends to scream rather than groan! If you have any clutch issues then it'll raise a fault due to detected slipping. A worn diff will whine. The groan may be the long driveshaft intermediate bearing or a wheel bearing if pulling the handbrake makes no difference. Also, it may be a rear wheel bearing as noise from them can sound like it's coming from the front.

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

Post by xantia_v6 »

I watched the tachometer while driving mine today, and it is not possible to get the engine labouring at 1500 RPM, at anything above about a quarter throttle, the transmission changed down to a lower gear to get the RPM above 2000.

You transmission is not going into "limp-home" mode is it? (only 3rd and revers gears available and flashing snow and sports LEDs).

A poorly performing engine usually causes shift points to increase in RPM rather than decrease, as the throttle is open wider and the manifold depression less.

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

Post by Mandrake »

xantia_v6 wrote:I watched the tachometer while driving mine today, and it is not possible to get the engine labouring at 1500 RPM, at anything above about a quarter throttle, the transmission changed down to a lower gear to get the RPM above 2000.
Thanks for confirming what it SHOULD be doing. :-D It definitely isn't doing that most of the time, and hasn't since I've had it. I just tried it again tonight - had to slow down on a hill following someone turning off, I got down to 20mph in 3rd just under 1500rpm, increased the throttle to see when it would shift down - I had to go to approx 80% throttle with the engine labouring heavily uphill before it finally changed down and zoomed away like it had just been stung by a bee. The torque converter was definitely in full lock up the whole time as well as there was no "flexibility" of the engine revs as I increased the throttle, it just sat at the same revs until the kickdown occurred, with just the grumbling from the engine increasing with the throttle opening...

I've never been happy with the downshift behaviour of this car, now and then it will downshift as I'd expect it to - it seems to be more reasonable in the more sporty maps (SK2 to SK6) but in SK1 (otherwise known as old man mode :lol: ) which it always seems to drop back to with around town driving (as confirmed by the Lexia) it labours the hell out of the engine and just won't down shift without more or less triggering a kickdown, which takes about 90% throttle. Sometimes it will let the revs drop as low as 1200rpm without changing down and require at least 75% throttle before it will change down. I know its a V6 which can pull lower than a 2 litre but in my opinion it shouldn't be working the engine that low under load...

On flat ground it can just cause an unnecessary loss of pickup but on a hill it can be impossible to gain any speed at all until you reach 80-90% throttle triggering a kickdown, at which point you're practically spinning the wheels with power and risking slamming into the car in front of you. (Should be fun in winter... :roll: )

The question is, what could be causing this... I would have thought that maybe the throttle signal was not being fed to the gearbox properly, but upon reading the training manual it seems that its sent digitally from the engine ECU to the gearbox ECU over a bi-directional serial link. The Lexia is reporting that the gearbox is receiving the throttle signal, although it only reports "idle", "mid throttle" (which covers 10%-90%) and "kickdown" which is 90% and over, so I don't know how accurate the mid throttle data is.

Anyone have any idea why the change down behaviour seems to be so wrong ?
You transmission is not going into "limp-home" mode is it? (only 3rd and revers gears available and flashing snow and sports LEDs).
No definitely not. :) I know what limp home mode is, if it had done that at any point you would have seen panicked posts from me on the forum by now :lol: I've had no fault codes logged by the gearbox since I reset the two codes that were previously there when I first got the Lexia. (codes posted earlier in the thread)
A poorly performing engine usually causes shift points to increase in RPM rather than decrease, as the throttle is open wider and the manifold depression less.
That's what I would have thought too.

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

Post by CitroJim »

Simon, what does it do if you keep it in sport mode but drive reasonably carefully?

Then pop it into snow mode and repeat.

I must say I've never noticed such to the extent yours seems to labour but as mine tends to spend nearly all of it's time in 'old git' (SK1) mode it does display some of the attributes you describe but with mine it just takes a moment for it to release lock-up and then pull strongly away.

You don't think there's a problem that it stays locked up when it should have released do you?

Wish you were nearer and I could drive yours, just to see what all this is all about from the driver's seat...

I still think the problem is with the engine and from what you say it seems to be lacking low-down power which should be very strong.

When I had a few issues with the MAP sensor on Mikes old V6, it was most unhappy but as mike said, it was keen to hang onto the lower gears and was reluctant to change up. In fact on the way to work one day I don't think it ever saw top however hard it revved. The only thing that provoked it into top was by selecting snow mode.

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

Post by Mandrake »

CitroJim wrote:Simon, what does it do if you keep it in sport mode but drive reasonably carefully?
Sport mode behaves as I would expect - with a light throttle it holds each gear up to around 3000-3500 rpm before changing up, on slowing down it proactively changes down a gear to keep the revs above about 2000-2500. No complaints with the downshift in sport mode, except there is quite a lurch from 2nd down to 1st. (only in sport mode)
Then pop it into snow mode and repeat.
Snow mode works more or less as I would expect - it skips 1st and 2nd, (I didn't realise until reading the training manual that it skips 2nd as well as 1st!) and changes up quite early, its probably a bit more reluctant to change down than economy mode, but I presume that is on purpose.
I must say I've never noticed such to the extent yours seems to labour but as mine tends to spend nearly all of it's time in 'old git' (SK1) mode it does display some of the attributes you describe but with mine it just takes a moment for it to release lock-up and then pull strongly away.
I see from the training manual that if the ignition is turned on while the gearbox oil temperature is below 50 degrees it defaults to SK2 for a few minutes - in this mode the downshifts are relatively ok, its only when it warms up and drops back to SK1 that it really becomes troublesome.
You don't think there's a problem that it stays locked up when it should have released do you?
Yes, that's exactly what I think could be wrong - the torque converter lock up is most often not releasing at low revs (1500 and below) under load when I would expect it to release to allow the engine revs to lift and build more torque, allowing for smooth pickup and acceleration. I see from the training manual that 2nd, 3rd, and 4th all have the ability to be fully locked, limited slip, or fully open depending on circumstances, and there are control tables for the lockup strategy as well as the gearshift strategy. I'm going to study those a bit more and see if what I observe is outside the normal parameters.

I'm pretty sure the same problem happens in all three gears that support lockup, and that it doesn't always do it. I have definitely seen occasions where the torque convertor lockup is NOT active in exactly the same circumstances - 2nd or 3rd around 1500rpm or just below, as soon as I apply even about 25% throttle the revs lift to about 2000 and the car pulls away smoothly and quickly, so it does seem to work at least some of the time.

Whether there is a hydraulic/mechanical problem, or the ECU isn't doing what it should is anyones guess.
Wish you were nearer and I could drive yours, just to see what all this is all about from the driver's seat...

I still think the problem is with the engine and from what you say it seems to be lacking low-down power which should be very strong.
Even well before the recent loss of power issues the down shift behaviour of the gearbox has always been as I describe, its just become a lot more of a liability since then engine running deteriorated. It is a lot better with the O2 sensor unplugged, anywhere from about 1500rpm upwards it pulls strongly now.
When I had a few issues with the MAP sensor on Mikes old V6, it was most unhappy but as mike said, it was keen to hang onto the lower gears and was reluctant to change up. In fact on the way to work one day I don't think it ever saw top however hard it revved. The only thing that provoked it into top was by selecting snow mode.
Hmm, exactly the opposite to what I get... its eager to change up gears but not down gears. :lol:

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

Post by xantia_v6 »

It occurred to me that when Stempy had a V6, he had problems with something he initially described as a misfire...

Here are links to some threads:
http://www.frenchcarforum.co.uk/forum/v ... f=3&t=6980" onclick="window.open(this.href);return false;
http://www.frenchcarforum.co.uk/forum/v ... 417#p31417" onclick="window.open(this.href);return false;
http://www.frenchcarforum.co.uk/forum/v ... 761#p92761" onclick="window.open(this.href);return false;
http://www.frenchcarforum.co.uk/forum/v ... 112#p77112" onclick="window.open(this.href);return false;
Was it a real fix?
Did you happen to end up with his car?