Suspension Dropping While Driving

[Alphadave]

Since buying the XM six weeks ago I've had a major problem with the suspension. It started displaying ´Hydraulic Failure´ and dropping while I was driving along. I had the spheres regassed (they were at about 30%) and all of the lines checked and tightened. The warning no longer comes up, but the suspension - especially the rear- still frequently drops. Itś not dependent on braking or steering, in fact itś usually while Iḿ traveling at constant speed in a straight line.

Current symptoms are:
* The car drops suddenly while driving. No messages or warning lights are displayed. It doesn´t drop low enough to scrape anything, but is quite noticeable.
* There is a lot of hissing and whirring under the bonnet. Hard to pinpoint exactly where, but mostly from the very front.
* The rear is very soft. I can push it right down with one finger. I haven´t had any other experience with hydraulic suspension, but it handles like a boat.
* No little green pee-stains on the driveway (no external LHM leaks). The fluid level is fine.
* Sometimes the suspension drops suddenly when the car is recently turned off. Several times this has coincided with using the electrical system (pressing the plip to activate central locking, turning the ignition back on etc).

After reading this forum I have the following list of suspects, with ideas for rectifying them;
* Internal LHM leak. I will check the return lines first – I assume this is done with the car running, at normal ride height?
* Clogs in the hydraulic lines. Will try using Hydraflush etc.
* Hydraulic pump failing. This is fairly expensive to rebuild/replace of course.
* FDV failing. Probably a similar cost as the hydraulic pump to fix.
* Pressure regulator?
* Electrovalves?

Any further ideas? Any suggestions welcomed. Iĺl update with info as I check things off.

[citroenxm]

Air trapped in the system???

TRY putting the car on LOW setting, then with the engine running open the regulator screw and leave it running for about 5 mins to completely drain any air locks that could be in the system, then re tighten pressure reg screw and see what happens from there....


rgds
paul

[Peter.N.]

Firstly, the rear suspension will always be much softer than the front as its normally carrying much less weight, if it really is ridiculously soft it can only be incorrect spheres, maybe you have a centre sphere in one of the outer positions.

Is the hydractive system working? the suspension should be in soft mode for about a minute or so after opening a door and closing it again, you should the hear a 'clonk' as the vavle closes and it should become much stiffer.

The hissing you can hear is probably due to the hydraulic regulator not cutting out because of pressure loss somewhere, normally it will stop if you increase the revs unless the loss is very severe.

As you say, check the return lines and that should give you an idea of where the pressure is going. Did you have the accumulator sphere repressurised?

Just check first that your hydraulic pump belt is not slipping.

Peter.N.

[jorgy9]

Hi Dave

don't worry, the reparation could cost you pennies but first we need to see what's going on. From your account I can imagine that:

-the previous owner has put some sort of less damped spheres at the rear (perhaps "comfort", perhaps CX spheres etc).
Only Hulk can push a normal spec XM down with one finger.

-the previous owner has put those spheres because his electrovalve stopped working so car became hard (middle spheres not opening up). This could be the usual cheap diode problem on the suspension ECU, but also some wirring problem. The dropping of the car could be due to random closing/opening of the electrovalve (ur XM has 1 of them). Could also be a leacky electrovalve.

-your pressure regulator is clicking alot it seems, can you tell how many seconds between "clicks"? Around 1 minute is great, near 5 secs is bad. Any ideas on the state of the accumulator sphere?

Do you notice any difference in hardness when u use the soft/sport switch on the center console? On your car it should give a permanent distinct difference. What if you plug/unplug the suspension ECU?

If you want to confirm whether it's the electrovalve doing tricks, you can plug a cheap voltmeter on pin No 1 of the suspension ECU white plug (or is it the black one?) and extend it to your car and watch while driving. I had done this to confirm that mine was OK. Normally this pin has to read a voltage of around 2.7-2.9volts when suspension is in "soft", ie car standing/engine running/doors closed, or, cruising on straight line. When it enters in "hard", you should see 0 volt for as long as it is hard. If you read a permanent 1.7 instead of 2.7, then it's the diode problem. If it switches between 2.7 and 1.7 then the diode is still "on the way out". If it plays between 0 and 2.7 without any particular reason, then there's a contact problem somewhere.

You're on a good track to find the problem, and u r right there's all u need to know on this site. Good luck and let us know.

cheers
G

[jorgy9]

ps. The "pressure regulator" is on the left hand side of the car between the engine and the radiator, at the low side of the engine. It has a sphere screwed on it -the accumulator-. You can see how it looks like in my Flickr website, there are some photos there.
G

[Peter.N.]

Defective diodes would fit the symptoms. If as you say the suspension drops when the ignition is turned off, this is what can happen, also when a door is opened. With faulty diodes the valve seems to stick partly open enabling depressurising of the central spheres - a bonus in fact!

Peter.N.

[DerekW]

Hi Dave,

The good news is that it is not going to be the hydraulic pump, that doesn't fit the symptoms.

You are doing the right thing by checking the return lines to locate leaks.

Slowly slowly catchee monkey, check one thing at a time, the cheapest first.

Derek

[Alphadave]

Thanks for all the suggestions.

I waited patiently for the weekend, when I would finally have a chance to work through them. I took it for another drive, and of course it behaved fine! The rear wasn't spongy, and it didn't drop once. I doubt that it's fixed though, so I started to work through the list. Then...




As soon as it melts I'll start on the car again. The accumulator sphere was repressurised last month. The LHM Reservoir and filters were all cleaned recently too. I'm sure that the correct spheres are installed, as I know the person who owned it for the last 15 years and the citroen specialist didn't mention anything. I'll check them anyway.

Is the Electrovalve expensive to replace? I can't see it on GSF.

[Peter.N.]

Hi Dave

You dont need to replace the valve, you can fit a diode in the ECU across the wires that go to the valve, if you'r not into electronics, there is one of our number who advertises a 'black box' on ebay that will do the trick.

Peter.N.

[citroenxm]

WOW Snow this time of the year? ! Is that normal? I Realise your not in the UK!

Electrovalves I think are expensive, however, if theres any XANTIA VSX models in breakers these are the same units I THINK as on S2 cars, but yours being an S1 im not certain.. others possibly will know this bit of information..


Paul

[Alphadave]

Snow isn´t unheard of this time of year, but it came quite suddenly this time. It didn´t last for long though.

I checked the rear spheres, as shown:

I'm not sure if you can tell from the markings if they're comfort/CX spheres, but I´d be very surprised if they were. The rear hasn't been nearly as soft in the last few days, maybe because I've been driving around in 'sport' mode - It feels so much better, and the back hasn't dropped yet! The little spring shaped light doesn't turn off with the ignition though - is this normal?

Is this the pressure regulator screw?

I can't safely try to bleed it until I get some ramps or suitable way of supporting the car.

I finally got my workshop manual back tonight so I can test the return lines tomorrow. Do these return line clips unscrew or just lever off? I have visions of green blood hemorrhaging all over the engine bay...

[dean]

Hi alphadave and welcome

That is the pressure relief screw (12mm head) but it will only bleed air from the distribution side of the hydraulics ie pressure regulator, flow distribution valve and pump, generally you undo the bolt about half to three quarters of a turn then start the car after work has been done on that part of the system so any air is pumped back to the lhm tank and vented rather than pumped into the brake and suspension circuits, then after a few minutes it is done back up. To bleed air from the suspension just jack the car up and down with the height control lever within the car several times, brakes are bled in the conventional way but you can do them on your own because the brake pedal doesn't have to be pumped just rest something on the pedal and you will get an endless flow to the calipers, unless you bleed so much out you empty the lhm reservoir that is . The clips on the returns will have to be cut off and replaced with jubilee clips or similar, do not take off the largest pipe on the far left, looking from the front of the car, as this is the feed to the pump, but replace the original clamp with a jubilee type one as this pipe is under a slight vacuum and if the clip is slack it will allow air to be drawn into the system and cause all sorts of strange stuff to happen. The other large ish rubber pipe next to it is the return through which the pump sends the lhm back to the tank when it is not needed, do dont take that off either. The other pipes will all be low pressure returns just have a rag handy to mop up the dribbles of fluid when you initially remove the pipes.
Your car has 1 remotely situated electrovalve rather than two that are built into the hydractive blocks like the mk2's had, so Roys box of tricks wont work on your car.

Regards and good luck
Dean

This post has been edited by dean on July 07, 2008 03:59 pm

[kenhall1202]

Hi alphadave,

According to Citroen Service parts info your sphere part number (96051827) shows that it is a genuine Citroen Mk 1 XM Hydractive rear (wheel) sphere, 400cm3 / 30 bars, (NOT a CX or Amtex / 'comfort' type).

The 0-179 marking may be a date of manufacture code but I don't how to decode it - does anyone else know?

Regards

Ken

This post has been edited by kenhall1202 on July 08, 2008 10:04 am

[Alphadave]

Thanks for all the info.

A gorgeous sunny day here today so I was able to really work on the car for the first time in weeks.

From checking the return lines:
* The return from the line on the far right, closest to the outside of the car had no fluid being returned. As this is not blocked off, does that mean I have a hydractive system? My manual says that this is from the hydractive electro-valve.

* The middle low-pressure line also had no significant return. I understand this is from the height correctors.

* The other low-pressure return, on the left next to the larger pipes had a constant drip, about 2 per second. If this is from the brake control valve, is it enough to be a concern/potential cause?

Next task is to bleed the distribution side via the relief screw. Can this be done with the car on a jack, or do you need ramps?

Last quick question, what is this? It's from another car, not mine. Is it the fdv? If not, what does the fdv look like?


This post has been edited by Alphadave on July 12, 2008 03:28 am

[DerekW]

That 'photo looks like an ABS valve block.

I don't have a diagram for the series 1, so I don't know if it's the return from the brake control valve. But if it is they are notoriously leaky, that's the main reason why the later cars were fitted with anti sink; but I would have thought that 2 drops per second is a bit much.

Derek