Pressure Loss, Car droping while driving

[adamufunbala]

Hey Guys,

I have been reading alot of information on this forum and I know am at the right place-meeting people who are experinced in Citroen issues.

I use an XM - 89 and I have had this problem for a long time now-where the car suddenly drops - both front and rear - while driving. I have gone from changing the pressure regulator, shock absorbers spheres, middle spheres, break unit, security valve accumulator (i dont know if there's anything like that), hight correctors etc. Recently, I learnt about bleeding the breaks and checking the current getting to the electro-valve-which I did and the car started behaving pretty well, like never before, but has just started losing pressure and droping again. I actually hear some heesing when I step on the breaks (is this normal?) and the presure regulator returns every 3-5sec.

Can someone please help me on this? I really need to find the solution to this problem, otherwise driving experince is terrible.

Thanks in anticipation to your responses.

Adams

This post has been edited by adamufunbala on August 05, 2008 10:28 am

[jackyboy]

I met a chap the other week at my golf club who had an xm 2.5td. He was saying that he had a problem with the steering suddenly going heavy(loss of pressure?)
The fault was located to a hose on the LHM resevoir which had a tiny crack in it. There was no signs of leakage so it wasn't obvious. Replaced the hose and problem solved.

[techmanagain]

Certainly sounds like a sudden pressure loss.
Are you losing any LHM as far as you are aware?
Otherwise - and I think more likely - you have a loose or leaking hydraulic sphere somewhere, and I would got first to the main accumulator, or if your car is a 2.5TD, the anti-sink sphere (though I never heard of one of those even being slack, much less loose!
Information on your model of car(in your signature) would be very useful as they are all different and diagnosis is a wild guess without it.
Have you ever had spheres replaced? If so , which ones and how long ago, and were they replaced on the car or off? Are there protruding valves on the end of the spheres and are they tight?
I could go on, but must have details of the car concerned.

[adamufunbala]

Hi Jackyboy,

Thanks, I'll check the hoses but I just replaced some of them recently, though I couldnt get the exact sizes but they worked well during this short fix. Do however think the break unit could be a culprit?

Adams

[adamufunbala]

Hi, tachmanagain,

I have made sure that I am not lossing any LHM, I have just replaced the main accumulator last week and there are protruding valves only on the shocks accumulators and not on all the others and I replaced the spheres last month.

[Ciaran]

Sudden, violent drops, are normally as the result of the ECU closing the closing the centre spheres with no pressure in them (something which it shouldn't allow to happen), then when they open again later, the fluid from the suspension spheres rushes in to fill the gap, causing the car to drop suddenly.

Even a drop from pressure loss in the system should be smoothish and progressive, if its a sudden, violent slam, rather than a sinking, then I daresay its the electrical issue rather than a pressure one.
If this is your problem, you need to be careful. The shock from sudden falls like that could damage your strut tops, rupture sphere membranes, and knock out other supports etc.

Is your suspension hard and bouncy?

Regardless, the accumulator cycling every 3-5 secs is far too soon, you do have a pressure drain somewhere. Likely suspects include the brake valve, you may be able to determine which circuit is returning excess fluid by pulling off the retuirn hoses at the reservoir and checking the volume of fluid. Any leaking components should be obvious by their steady stream of returning fluid.

[adamufunbala]

Thanks Ciaran,

Once the car is up, the sides bounce ok and are not hard - just ok - but you know when it loses pressure, it becomes very bumppy and i feel how the impact lies on the support.

I have actually not done anything around the ECU but have checked on the electro-valve under the car around the driver's seat and the amount of current getting there is ok (around 2.7-2.9), so I thought this proves that the ECU is fine.

Now if the return hose that returns large amount of fluid is connected to eg the brake valve- does this mean that the valve is the faulty component?

[Peter.N.]

The strange thing here is that the front and rear are dropping, this points to a complete hydraulic system failure, but that would cause loss of power steering as well. In normal driving, the front and rear sections are seperated by the height correctors, even if you lost all pressure it shouldn't cause either end to drop unless both height correctors are very leaky! Failure of powert to the electro valves should not affect the height, only the ride, they just isolate the centre spheres - very strange!

Peter.N.

[adamufunbala]

Hello Peter. N.

Thanks, sorry I need to clarify that they dont drop at the same time, they do interchangably but mostly the back drops when the car is parked eg right now the car's parked, the back has droped but the front is still at normal hight but while driving they interchangably drop and no loss of power steering

[Peter.N.]

The only other thing I can think of is that the height correctors/linkages are sticking, have you tried lubricating them? two or three applications of WD40 should help, or better still, ordinary engine oil

[Peter.N.]

Another thought hs just struck me. Ciaran mentioned the ECU, I have observed that if the diodes in the electrovalves are faulty, they dont open right up, they stick somewhere in the middle and this can allow the fluid from the centre sphere to enter the outer spheres. I have observed this when the suspension is on its lowest setting, if you open a door the suspension will 'jump' and then settle down, in this way you can depressurise the centre sphere - but it doesn't always work like that. Under these conditions the suspension will be stuck in hard mode, is yours? I have had to fit diodes to both of mine!

By the way 'Welcome to the club'

Peter.N.

[Andmcit]

By the sounds of things, all the items being suggested have been replaced; I trust by
new or known good second hand items.

The middle spheres and height correctors are on the list as well as the pressure release
valve among many items.

Initially I'd thought middle sphere as Ciarán but am now actually wondering if an anti roll
bar linkage onto the height correctors is actually slightly loose swivelling on the anti
roll bar, thus sending all kinds of contradictory orders to the height corrector?

Possible?
It's either something bizarre like that or witchcraft trickery hiding in the electrics. As
read elsewhere on the forums, if it can't be fixed with judicious use of a lump hammer,
it'll be an electrical problem...

Andrew

[xmexclusive]

Hi All

Just a couple of comments on the above posts.

An anti sink sphere is connected differently to other spheres and so will not leak LHM even if it comes loose. The sphere threads push through the mounting bracket and a large nut screws on to hold it in place. The only hydraulic connection is a 3.5mm pipe and nut into the centre of the anti sink sphere.

In this months Citroenian there is an interesting note by the Xantia expert about suspension ECU's getting stuck in hard mode due to repeated service faults. It would seem that if an ECU collects enough service faults it will lock itself and therefore the car into hard mode. It would appear that it is not enough to identify and just repair the suspension faults. It is also then necessary to use an ELIT or similar Citroen diagnostic tool to read the fault codes and erase them to get the ECU to work in soft mode again.

The thought that a correctly repaired car will continue to malfunction until the ECU is reset just about made my day. If this is the case then it could really complicate suspension fault finding and repair not to mention similar problems with the other types of XM ECU.

Regards

John

[Norman]

Hi All,
I also read that so i mentioned it to my indie who said !!!! but said he would plug my car in and see at the next service,
I wonder if Mr Mackay has heard of that one as he repairs Suspencion Ecu's.
Regards.
Norman

[Ciaran]

My original S1 used to do this quite a lot and it was the ECU / electrovalves. It would often do it when sitting idle, if a door was opened for example. The only way I ever found to get out of this vicious circle was drop the car to min height and reset the ECU by unplugging it. This would then open the centres again and allow them to be pressurised normally when the car was started.

Even if a car is getting stuck in hard quite a lot, this doesn't mean the middle sphere problem can't occur.
I'm not sure how the situation comes about where the centre sphere becomes devoid of pressure and is then closed and later opened, but if the car was regularly in hard then it would mask this issue most of the time until the rare occasion when the centre spheres do open for whatever reason.

I do think Andrew's point about the height corrector linkages is worth investigation too.

Ciarán