Sudden Drop, hydraulic

Right folks, I've had my 94 XM 2.0i auto for 5 months now and have covered 8000 trouble free miles. Now MOT is up I think I will keep this car and fix/service it up properly.
The first thing to sort is that LHM fluid that looks like muddy water a momment
Next is to sort out why when I turn off engine and open drivers door the car drops quite quickly at the rear?
If I turn lock to lock while say doing a 'U' turn why does the steering go lumpy and heavy?
Why did my Citroen main dealer look baffled when I said I wanted to change all my spheres, whats the matter does nobody do this?

Here is a nutty one, I have owned just about every brand of car and many models from each brand and many Japanese including many 4x4s and new ones at that,
but this XM has been the cheepest most comfortable and reliable motoring ever.
Am I lucky ?

No, you'r not lucky, (well maybe with it being the cheapest, if you are referring to the cost of maintenance), all XMs are like that. Hydropnumatic cars are the only ones that can give you the best of both worlds, soft suspension for straight line driving and stiffer for cornering.

As for changing spheres, this is usually done on an as needed basis. If you can bounce each corner of the car about 4 - 6" with the engine running the suspension spheres should be OK, also listen to the clicking from the pressure regulator, if it more frequent than about 15 - 20 seconds you will need a new accumulator sphere.

A change of LHM fluid and cleaning of the filters will certainly do no harm and may even improve that sinking feeling.

For your lumpy steering on full lock, check the hydraulic pump drive belt tension, sounds as though its slipping.

Peter.N.

I think your hydraulic system needs a good cleaning with hydraflush for a couple of 1000s miles, and then many of the problems you describe will sort out themselves -your LHM sounds nasty-.

George

First thing I would do is to replace the LHM fluid and to clean the filters, due to the severity of the LHM condition you expressed it may be of added benefit to drive on some Hydraflush and then replace with LHM...after this some of the problems will most likely disappear.

Peter would appear to be bang on regarding the belt.

Cheers for that chaps, Here's a funny one after gaining a bit more tension on the pump pully I sat in the car and engine running turning steering wheel from lock to lock I found that the effort required was alot less if I increased engine speed. The pump sounds like a small machine gun on start up. I have a spare pump and a pile of other bits donated to me from local garage because they think I'm having a crisis , so first should I change pump before LHM or just stick to LHM change and see what happens??

Sounds suspiciously like pump is kaput to me!

Hi trailsuperten,

When your car is sitting parked for a couple of minutes (engine off or engine on) the electrovalves which connect both centre spheres close and the spheres are isolated from the rest of the hydraulic system. If the engine is running the electrovalves will open periodically and close again. This equalises the pressure stored in the centre spheres with the pressure in the rest of the system. One of the triggers to open the valves is opening any door or the boot lid.

If the pressure in the centre sphere is the same as or close to the pressure in the respective circuit then you'll feel no change in th ecar. However, if the pressures are significantly different then youll sense the car rising or falling accordingly. If the circuit has lower pressure than the sphere then the car will rise because the contents of the sphere will be forced out and increase the pressure in the circuit. If the circuit has higher pressure than the sphere then the car will sink because the contents of the circuit will be forced into the sphere and increase the pressure in the sphere.

Therefore, your rear electrovalve is not opening sufficiently whilst running to keep the centre sphere pressure up. When you park and open a door the electrovalve opens and the fluid in the circuit rushes into the 'empty' sphere and the rear of the car sinks. The fact that it sinks suggests the valve is working but not at the right time. The intermittent nature of the problem suggests the likely culprit is the MOSFETs in the ecu are overheating due to a bust freewheel diode in the electrovalve solenoid.

There's a self-help file here showing how to fix it:
http://club-xm.com/forum/index.php?showtopic=845

Please let us know how you get on.

Cheers

noz

OHHHHHH, Noz I cant open the ecu help file, the computer says no, well it actually it says the is an error opening this file, what do you reckon?

Do you have an up to date version of Adobe Reader?

Download free from www.adobe.com.

No problems opening the file here.

Now we are cooking cheers for the pointer John.
This evening I thought it would be great fun to try a different pump even though the one fitted works ok, its noisey at times.
What a difference that made quiet and has completely taken care of the lumpy power steering. Result
Also tried some different front spheres as suspension travel is only 1 to 2 inches with the palm on slam panel test. Well talk about giving your car the suspension of a go-kart brand new fronts on Wednesday and change LHM.
Interesting stuff about electrovalves and the effects from sensors around the car, I hope most of the presure inadiquacy's have been sorted with the pump there's always a chance the soldering iron will come out
Many thanks again chaps, I'll keep you posted,
Marcus.

Please do not just change LHM but put hydraflush (aka flushing oil) in it, from your description of the current LHM, your car really needs a clean. Run it on hydraflush for 1-2000miles and then put fresh LHM. Ideally, put the old pump on during the "cleaning" period as to avoid contamination of the good one you have (with hydraflush alot of gunk gets moving around the system, and you might experience strange suspension effects during that period). Also don't forget to clean the 2 filters in the LHM tank.
George

Right then, today 2 new (allegedly) front spheres, a change in LHM rather than flush as old stuff was more dark yellow than brown.
The filters were solid
Result is a smooth level ride and the car stays up after engine stopped. Things are getting much better, or so I thought
I noticed some steam emmiting from the exhaust manifold area, looking closer I noted that water was escaping from a crack in the manifold while engine ticking over. Head gasket then well at least it happened on my drive so it's in bits now..........

F**k!! Courage then!!

George

All back together and running nice
This XM has its own 'you will fix me system' because what it wanted was a cam belt and the only way to get me to have a look was to blow the head gasket.
That was so close as it really did need a cam belt.
Anyway, back to hydraulics things are feeling better now and all appears to be ok, if it goes wonky again electro valves and ecu will be first on the list.
Thanks Chaps for all your input ,
Marcus.