My Citroen XM 3.0 PR-Vestige

[Dean]

I think you are correct, I picked up some oil and a fuel filter this morning, topped the transmission up and fitted the new fuel filter (pain in the backside to get to) and have covered 50 miles so far today.

The gear oil is still clean but I will be changing it again tonight or certainly before the next spell of use.
After much driving and being able to assess the situation I am fairly sure the engine is intermittently missing under load which is causing the vibration as at one point today it smoothed out completely and pulled very strongly.
When restarting from warm earlier the engine missed a bit for the first few seconds so there could be a little fine tuning required, maybe worth another look at the injectors, fuel pressure regulator and ignition system, maybe a duff lead or two somewhere on the HT side.

I will start by pulling the new plugs and seeing what they have to say.

I'm nearly there!

D

[Dieselman]

That sounds like low fuel pressure.

Now you have changed the fuel filter you might be best to drive it for a bit to get everthing back into working operation, then have a deeper look. The fact that it suddenly ran ok indicates there isn't a fundamental problem.

[Dean]

Yes, this evening on the drive back home it ran better earlier in the trip and not so good later, as i got closer to home confidence grew to give it the beans as it was all down hill to the drive from that point!, under load in a high gear you can feel the power pulsing on and off slowly and randomly, at full throttle it revs happily but surges on and off heavily and delivers maybe half its power.
The exhaust smells of nothing, just warm air, i didn't sniff it too long but it doesn't smell of anything so fueling must be correct and maybe a touch lean at the outside (at idle at least).

Might look at the MAP sensor too or take it for a drive with the live data running on the lexia to see what its doing.

D

[Dean]

I have had a little break from the car for a few days this week, had some cross-industry meetings and seminars (read paid for piss up's in posh hotels) but I had the day off today and felt like a fiddle.

To start off I fitted the rubber protector to the brake valve, what a lovely job that is, pop the scuttle off, remove link arm and brake valve securing screws, lift brake valve up and rest on top of it's mounting bracket, pop old ring and seal off, fit new seal with old ring. DONE, Very satisfying job that one and it put me in the mood for chasing the vibration.

The long and short is i have pinned down the vibration is engine related and is only at Partial load, just a nats whisker either side of neutral throttle will bring it on and is worst at 1100rpm and 1800rpm also when initially pulling away.
No vibration at idle but will vibrate if revved in neutral.
The exhaust is not touching but fiddling with the exhaust improved it slightly before, so im kind of stumped on that one at the moment and shall look into it in more detail later.

After eventually sorting the Lexia out plugged it in for some live data from a cold start and found it all looked really good, HERE is a link to the video i took of it to mull over later but i think it looks great, comments welcome if you think anything looks a bit off. I took the car out to heat the gear oil up for another transfusion and the vibration is much better (i haven't done anything to it!) and it pulled a lot better too but does still stumble or surge under heavy acceleration.

Checked the fault codes and there is an intermittent fault for the O2 sensor which would suggest to me there is a fueling issue as that O2 sensor is from the Prestige and was pretty new and working well as the live data suggests.

Changed the trans oil anyway, looked ok on the dipstick but it really is not
IMG_3358 by Deanxm, on Flickr
IMG_3356 by Deanxm, on Flickr
IMG_3357 by Deanxm, on Flickr
The filter looks good and clean this time though, another fluid change is in order in another 50 miles i think! and i will be keeping a close eye on it for another change or two in the coming week
The engine is a little coarse when cold, more so than the 2.0 was but ok when warm.

D

[Dean]

Mind you having watched the video i notice the O2 sensor does drop to 0v on several occasions which can't be correct, the fuel trim deviate's from the norm and seems to be adding extra fuel or trying to, i think i will take it out and see what the O2 sensor and fuel trim has to say for itself under load and at WOT.

D

[Dieselman]

Have you checked the lower torque bushings for wear? The metal bracket can transfer vibration if either the engine side, or subframe side are worrn.

If the torque converter lock up clutch, or any of the transmission friction linings are becoming detatched, that causes vibration under load. Glycol rapidly kills the adhesive used in auto gerboxes, and to a lesser degree, wter.

[Dean]

I got very intermate with the lower bushings among others and they are perfect.
Looking at the oil i was worried about water loss but the water level sits where it did with the 2.0 engine which is about 3mm below the marker in the header tank and has not moved.

The vibration is worse when cold and at low revs and non-existent under any kind of load or at high revs, its strange.

D

[xantia_v6]

Have you considered that the vibration could be due to a mis-timed balance shaft? The balance shaft has most effect when the engine is lightly loaded, and if mis-timed would probably have a resonant frequency or two.

[Dean]

I hadn't thought of that, no.
I would hope not as I've already messed up the timing once and had to go back in! but it's a good thought and at least if that were the problem it would only be a quick half hour job to sort it out.
I shall look at the photo's and check.

D

[White Exec]

Our 2.5 ran for several years with one of the balancer shafts one belt-cog out, following routine belt replacement by Citroen in the UK!
Was spotted when we did an engine-out HG overhaul here, by a good mechanic who had marked everything up before he dismantled.
I was lucky enough not to have any rough running, but after the overhaul, engine was left delightfully smooth.