Xantia supension issues

[Xaccers]

Also, remember on Xantias the sports mode doesn't put the suspension into hard mode like early XMs.
It just lowers the threshold at which the switching to hard takes place.

[DickieG]

Another thing is the anti-sink function seems to 'stick' and when I start it up in the morning it drops with a harsh thunk before rising up to normal (insofar as the lever's at normal)...

I'd say that the "Thunk" is the Hydractive valve opening and with the ride height being much higher than normal when it releases it causes a much greater rush of LHM than if the ride height was set correctly hence the louder noise.

[Dommo]

Good thinking on the thunk being the electrovalve

Dommo, I think you've got the hard and soft modes mixed up as far as LHM leaking back to the tank is concerned otherwise your car would sink onto its bump stops when parked if it leaked in hard mode as that is the default position for the Hydractive valves. A well known cure for leaking Hydractive valves is to remove the Hydractive fuse to force the suspension into hard mode to stop the leak.

Most, if not all Hydractive S2 Xantia's drop a little a short while after start up, certainly all the S2 Xantia's I've ever driven have done this and as the Xantia in question is a very late S1 I'm wondering whether it has the slightly different S2 plumbing of the suspension.

Trust me it definitely leaks back to the reservoir when in hard mode, but the electrovalve and anti sink system is strong enough to keep the corner spheres isolated and pressurised.

[CitroJim]

I've not got the time right now but hang on in there for a while everybody and I've been here and have extensive knowledge of leaking hydractive valves; some gained very recently

It needs an explanation and it *may* also account for why you're riding high Phil, well not you as such but your car...

Sorry time precludes right now. I'll do it as soon as I can...

[xantia_v6]

I think that Jim's "recent" experience was gained on my car.
It has for a long time (perhaps for the 7 years that I have owned it) been prone to sticking in hard mode at the rear, with the rear end often dropping suddenly after driving half a mile or so (sometimes triggered by driving over a speed-bump).

A year or two ago, the rear electrovalve announced its leakyness by pressuring the leak-back pipe and popping the T-joint apart a couple of times.

Also over the last year or so, the back end has been increasingly reluctant to go into soft mode, often becoming semi-soft where the rear end could be pushed down once, and then just stay down until the height corrector kicked in.

It also developed a habit of the rear height corrector over-correcting (at least in the semi-soft mode), so that with the engine idling, the rear end would oscillate up and down about 2 inches over a period of about 30 seconds.

Perversely, I once loaded the car up with bricks to within 10 bricks of the load where the rear suspension could not rise off the floor, and soft mode magically returned for that one journey (it really was soft mode, not just the inertia of the bricks).

Jim and I had looked at it a couple of times, but other more urgent stuff had always prevented much remedial work.

The spheres were all recent and correct, the pressure regulator had been changed (with no change to those symptoms).

We could not decide which part to change next: the height corrector or the electrovalve or the whole rear hydroactive block.

Anyway, last weekend I changed the rear electrovalve, and all of the symptoms have gone, it switches cleanly between modes, there is no oscillation, and the system now retains enough pressure that it will switch to soft mode on opening a door even 10 minutes after stopping the engine (previously it was probably 10 seconds).

One other symptom to note is that with the old electrovalve, there was no audible click when the electical signal was removed.

So that is the story of the symptoms and cure, I will let Jim have a go at explaining what was really going in internally...

[citroenesque]

It's going onto the ramps on Thursday when, I am assured, it will be resolved. MOT time too, so fingers crossed.

[CitroJim]

Thanks Mike That's exactly what I was going to speak about Just to add, all the strange behaviour can be placed on the rapid loss of pressure through the electrovalve causing the anti-sink valve to come into operation, effectively isolating the height corrector from the suspension spheres and thus causing the suspension to stay artificially high or low.

A good valve will click when operated, hum steadily whilst operated and then click loudly when it switches off. The loudness of the click is determined in part by hydraulic pressure available so if the system is fully discharged or pressure is very low, due to excessive leakage) then the "off" click will be very weak; as was the case on Mike's. If the click is weak then the valve is not shutting as it should and stays in a limbo state where the leakoff port remain partially open.

If the valve is really leaky then it is likely also to make a "flushing loo" sound as it clicks off; the noise the LHM makes rushing out of the leakoff port.

To fully confirm it's the valve and not the ECU drive signal, it's a good idea to pop an oscilloscope onto the valve feed and see a nice 30/70 squarewave present. A duff diode in the valve can also show very similar symptoms and again a 'scope will soon show if this is the cause.

I leave the subject of repairing electrovalves to another time...

Sorry I'm late posting this. Got home from work late, the phone rang off it's hook, I had my CCC column to finish and Xac posted a picture of robots in French Car Chat. That last one distracted me terribly

[DickieG]

If I'm ready this correctly the problem described relates to the ride height being incorrect/oscillating, the issue of the valve opening a short period after starting is a separate matter which is common on Hydractive S2's.

[citroenesque]

Yep, it's simply the ride height issue giving me problems because as it's riding high the suspension isn't operating in 'normal' as well as it should - it feels somewhere between 'normal' and 'high/intermediate'. I am assured the ride height issue will be fixed on Thursday - Dennis is confident (and a tad apologetic!) - and the issue of possible rear electrovalve problems is going to have to wait to be resolved. MOT to get first!

Jim, I found the robot thing distracting - I did find him in the end though

And Jim, I know you said you didn't think I needed the diode kit fitting, but do you think I should now? (If so, can we fit the one you said you had at Little Horwood? lol!)

Phil

[Dommo]

Interestingly it's my S1 that has the flushing toilet sound.

The electrovalve clicks on and off quite nicely too from what I remember, it still leaks in hard mode though.

The noise while the electrovalve is on is quite varied, the tone changes. Is that an ECU issue or valve/diode issue?

[CitroJim]

Phil, yes, always a good idea to fit the diodes... Can be done at Little Horwood, no worries...

Dom, Could be diodes. Best way to check is to get a 'scope on it and see a waveform like this example of a good one.



If the edges of the squarewave look ragged with lots of 'ringing' then the diodes are needed as a first step. If the amplitude is low then the ECU driver IC may be faulty. You should see 12V peak to peak.

As I said above, fit diodes anyway as a precaution, it won't hurt.

[citroenesque]

Phil, yes, always a good idea to fit the diodes... Can be done at Little Horwood, no worries...

Excellent. Just have to hope the Xantia passes the MOT tomorrow!

[citroenesque]

After a long list of jobs completed (although it's still riding maybe 1/4 inch too high overall, but I'll see how it 'settles down') and driving really quite nicely, it's just passed it's MOT with no advisories.

Relieved.

[DickieG]

That's good news

[CitroJim]

Excellent news Phil