That sinking feeling... Xantia VSX

citroenxm · Post by **citroenxm** » 16 Nov 2006, 20:41

Hi all

I am currently useing a 1995 M reg, Xantia VSX Td.. However, it runs like new as far as the engine is concerned, but, however, when I stop the engine the car takes no more then 15 seconds to drop to the floor!!!

Its not a sudden drop, but just like I've put the suspension lever on low, and its only the rear that drops.

If I then start the car again right after its settled, it takes over a minute to rise up to normal height again! However, I did discover that if I pump the brake pedal furiously while its pressurising the STOP and pressure light comes on.. This bit could be normal however as its exhausting the accumilator sphere.. which incidentally IS NOT flat..

The car rides perfectly other wise, its just when stopped it drops to the floor..

So, Am I looking at the Regulator unit on the front, or the anti sink system?? My guess is the regulator due to the time it takes to pump up again.. even cars WITHOUT anti sink rise quicker then this does.

Can anyone confirm or correct me??

Many thanks

citroenxm

Post by **RichardW** » 16 Nov 2006, 21:18

They all do it sooner or later.... my 97 VSX does too - and has done since I got it (2 years / 40k ago!). The most likely cause is internal leakage in one or other of the hydractive electrovalves (probably the front, they seem worst afflicted!). You will probably hear a click followed by a hiss a few seconds after you switch off. You may well find that if you unlpug one of the valves, the symptoms will go away - of course you can't really drive it like that as it will be hard as nails! Unfortunately the only real solution is replacement of the electrovalve - and they cost > a ton from the dealer. You could replace it with a known good 2nd hand one - the front and rear are interchangeable, and the rears as I said seem much less afflicted.

If it still does it with the valves unplugged, then you are probably looking at a failed rear cylinder.

I do like the hydractive cars' ride, but finding a HDi 110 Exclusive replacement is proving elusive. so I am probably going to have to go back to a 'normal' Xantia!

slim123 · Post by **slim123** » 16 Nov 2006, 21:35

Starting at the bottem of the question! The reason why a Xantia without anti sink is quicker to rise, is that it has a more powerfull pump than cars with anti sink.

Early cars ie without anti sink are fitted with a 6 piston pump, this pump supplys the hydraulic system with all of the pressure needed for suspension, brakes and steering.

Later cars ie with anti sink are fitted with a 6+2 pump. This pump is a single unit split into 2 x parts but both sharing the same feed pipe and reservior. The 6 piston part of the pump supplys flow and pressure to the power steering only, whilst the suspension has to lift only using 2 pistons, so is therefore slower to lift.

The 2 x pistons are more than enough to keep the suspension and braking system working as they also have the main accumulator sphere supplying pressure as needed. In fact the early DS the early CX and the GS/GSA only used a single piston pump, as there was no power steering to draw the flow of fluid.

The reasons for the sinking, I would guess at an internal leak in the system letting fluid seep back to the reservior through the return lines, this in itself shouldnt be too hard to find as with the speed of sinking there should be quite a fast run going through.

Most likely suspects, the brake doseur valve or one of the rear suspension cylinders. To check these, pull off the return lines, there should be no more than a dribble of fluid returning.

Very very doubtfull if the regulator could cause the sinking, as if so it would probabaly go down all around and even.

Anti sink system will again be doubtfull if it's causing a problem, if you have a leak back, even an anti sink system will not keep it up, the anti sink system is only going to work is everything else is fine!!

Regards
Slim

Mandrake · Post by **Mandrake** » 17 Nov 2006, 03:39

RichardW wrote:They all do it sooner or later.... my 97 VSX does too - and has done since I got it (2 years / 40k ago!).

Where do you get that from ? Sinking in 15 seconds is a pretty unusual problem, (I've only seen it mentioned on this forum a couple of times) not a comon one, nor an inevitable one...

The most likely cause is internal leakage in one or other of the hydractive electrovalves (probably the front, they seem worst afflicted!). You will probably hear a click followed by a hiss a few seconds after you switch off. You may well find that if you unlpug one of the valves, the symptoms will go away - of course you can't really drive it like that as it will be hard as nails! Unfortunately the only real solution is replacement of the electrovalve - and they cost > a ton from the dealer. You could replace it with a known good 2nd hand one - the front and rear are interchangeable, and the rears as I said seem much less afflicted.

I don't think theres any way that a leaking electrovalve can cause this problem on an anti-sink model - yes it could happen when a specific seal failed in the electrovalve on the early non anti-sink models, but the specific path of leakage this caused is prevented by the anti-sink system.

Going down that fast theres really only a couple of possibilities - the brake doseur valve is leaking like crazy, or one of the rear suspension cylinders is leaking like crazy. (And a slight chance its the height corrector)

Here's how it should be possible to isolate which one it is - first I'd try setting the height control lever to the high position just as the engine is switched off, and if the back still goes down its probably not the height corrector.

Next thing I'd try (engine back on again and height lever at normal) is once the height is stable, open the main pressure regulator bleed screw half a turn then turn off the engine.

This will cause the anti-sink valves to immediately close. If the back now stays up you know that the leakage is not the cylinders, and is almost certainly the brake doseur valve. (The anti-sink valve has now isolated the doseur valve from the suspension)

If it still goes down just as fast when the bleed screw is open, either one of the rear suspension cylinders is leaking like crazy through one of the return pipes, or the anti-sink valve itself isn't working, in addition to the main problem.

Thats my take on things anyway!

Regards,
Simon

Post by **RichardW** » 17 Nov 2006, 07:54

"Where do you get that from "

Almost all the adverts for hydractive cars in the UK show them sunk at the rear...

Mine drops to the stops at the back approx 15 - 30s after the engine is shut down, and it takes anything up to 1/4mile before the STOP light goes off. I have always assumed that it was the hydractive valve, as I have the click + heavy hissing from the front soon after shut down - which is almost exactly the noise my mate's 94 VSX used to make, before dropping itself flat on the floor.

Richard Gallagher · Post by **Richard Gallagher** » 17 Nov 2006, 16:37

RichardW wrote:"Where do you get that from "

I've owned several Hydroactive Xantia's and I can't say that any of them have sunk at the rear.

With 'anti-sink' fitted and if left for several days, they would eventually sink, but evenly.

citroenxm · Post by **citroenxm** » 17 Nov 2006, 17:10

Richard Gallagher wrote:
RichardW wrote:"Where do you get that from "
I've owned several Hydroactive Xantia's and I can't say that any of them have sunk at the rear.

With 'anti-sink' fitted and if left for several days, they would eventually sink, but evenly.

Hi All,

Thanks for your thoughts, I'm NOT new to Xantias, having owned a few and worked on a few too, but I've had NONE behave like this one is..

Mandrake, I like the sound of your testing, and shall try it over the weekend, if it stops raining for long enough!!

I have an 1995 Xantia SX non hydractive but with anti sink, I pumped the system up on that car LAST sunday with a drill in the HP pump (Yes it worked) today (Friday) without a battery fitted the car is STILL at the same height position I left it in.

I DO NOT mind the car sinking AT ALL, but its the SLOW time it takes to come up, EVEN immidiatly after stopping the engine and trying again!

Thanks again..

citroenxm

PS: Anders, your thoughts on this??

jeremy · Post by **jeremy** » 18 Nov 2006, 08:22

I think your anti-sink valve has developed a problem. Its function is to maintain full height regardless of leaks in the brake valve and height corrector.

Have a look at Gabor's excellent textbook - under technical guide on the Citroen DIY site and you will find a good explanation of its function with diagrams on p35.

http://www.tramontana.co.hu/citroen/index.php

slim123 · Post by **slim123** » 18 Nov 2006, 09:36

Sorry but the anti sink valve will not hold up a car with a return leak on the brake valve or rear cylinder! It cannot hold up a car whilst fluid is seeping back to the reservoir, unless the engine is running to top it up!!

I have read with interest the pages mentioned in the link given, it is a very good guide, but there are some quite big flaws in odd places.

Example quote from wed page.
"Turn the steering wheel from side to side (on models with power steering). if the pump runs continuously while you do so, the main accumulator or the front spheres are suspect."

The power steering does not use the main accumulator or the front spheres for fluid, it works direct from the pump!

As suggested, check the returns from the brake valve and rear cylinders.

Regards
Slim

Mandrake · Post by **Mandrake** » 18 Nov 2006, 10:47

slim123 wrote:Sorry but the anti sink valve will not hold up a car with a return leak on the brake valve or rear cylinder! It cannot hold up a car whilst fluid is seeping back to the reservoir, unless the engine is running to top it up!!

You're right, sort of...

Leakage from the rear suspension via the brake valve is the major contributor to the rear of a non anti-sink model going down (in half an hour to 2 hours or so), and is precisely why the anti-sink system was developed in the first place - to isolate the brake valve from the rear suspension, and to isolate both height correctors from both the high pressure supply input and the suspension. (The height correctors being the other normally "leaky" devices apart from the brake valve)

However there is a proviso to this - because the anti-sink valves work on pressure differential between the high pressure supply and the suspension, if there is very rapid leakage via the brake valve (the kind of leakage that would cause the back to go down in 15 seconds) the anti-sink valve cant stop it, because the anti-sink valve will remain open - the high pressure supply is greater than the suspension pressure at all times.

In the normal course of events the anti-sink valve relies on the main system pressure dropping faster than the suspension pressure when standing. Once the main system pressure drops below the suspension pressure the valve closes, and the suspension is isolated from the height corrector and brake valve.

This was the purpose of my test opening the bleed screw - by forcing the main system pressure to instantly dissapear before the car gets time to sink, the anti-sink valve will close immediately and isolate the brake valve - if the sinking doesn't occur, either the brake valve or height corrector has gross leakage.

If it sinks the same as before, either the anti-sink valve doesn't work, or the leakage is the one of the cylinders.

As you say, the anti-sink system can do NOTHING at all about high leakage from the cylinders, making them the most likely culprit. (Depending on the outcome of the above test)

The leakage from the cylinders is normally exceptionally low - an anti-sink model can stay up for about a week, and that gradual loss is almost entirely the cylinder leakage.

I have read with interest the pages mentioned in the link given, it is a very good guide, but there are some quite big flaws in odd places.

Example quote from wed page.
"Turn the steering wheel from side to side (on models with power steering). if the pump runs continuously while you do so, the main accumulator or the front spheres are suspect."

The power steering does not use the main accumulator or the front spheres for fluid, it works direct from the pump!

As suggested, check the returns from the brake valve and rear cylinders.

Regards
Slim

I suspect that quote was written prior to the 6+2 pump arrangement of later XM's and Xantias, (most likely for the CX, which DOES run the power steering off the main accumulator) but even then it is inaccurate as you point out. There are quite a number of small errors and misrepresentations in that document that I've spotted over time, but it doesn't stop it being a good overview/introduction for newbies...(as long as they realise there are a few mistakes in there..)

Regards,
Simon

Post by **RichardW** » 18 Nov 2006, 12:09

My money is still on the hydractive valve(s). This symptom only affects hydractive cars, and on mine if you stay in the car for 15s after you shut the engine down, then get out, the suspension rises, but does not correct itsself - it can't because he HA valve has dumped the system pressure and closed the AS valves. The car will sit happily in this risen state for quite a while, then when you start the engine and get suspension pressure it will drop back to normal height.

Post by **philhoward** » 18 Nov 2006, 20:58

My experience of Xantii (is that the plural?) has all been of Anti-Sink cars - 2 of them HA2 VSX's. All of them have normally fell after starting them (as soon as the stop light goes out - pressure opens the AS valve), but they've varied by how quickly they sink. For some reason, however, the non-hydractive one sunk at the back first; the HA-equipped ones always sunk at the front first (the last one still had its back end at full height nearly 4 weeks after the rest of the hydraulics died!)

citroenxm - it sounds like either the hydractive valves are leaking, or they're being told to stay open by the ECU for some reason (and there are a lot of things which could confuse the ECU to open the valves such as the steering sensor, doors open...). I never figured out why the HA valves kicked in when you opened the door, though!

Mandrake · Post by **Mandrake** » 18 Nov 2006, 21:47

philhoward wrote:My experience of Xantii (is that the plural?) has all been of Anti-Sink cars - 2 of them HA2 VSX's. All of them have normally fell after starting them (as soon as the stop light goes out - pressure opens the AS valve),

Ever since I've had it, my car has always dropped suddenly at the rear by about 1 inch after starting it in the morning at about the time the Stop light goes out, and I always assumed it was to do with the Hydractive control block operating when enough pressure is available to switch it into the soft mode. (Allowing pressure to equalize between outer and centre spheres)

However I just recently replaced the anti-sink sphere, and guess what - the sudden drop when starting in the mornings has completely gone

The old sphere was left lying with the hole facing the ground and after about 20 minutes it had slowly leaked about 200 ml of oil so clearly the diaphram was punctured.

So it looks like the drop is caused when the anti-sink valve opens, but the anti-sink sphere is not functioning. On the downside it now takes longer for the rear to lift after replacing that sphere

Replacement of the anti-sink sphere hasn't really had much effect on how long it takes to go down though, BUT, the rear brakes seem quite a lot sharper and more responsive now, so I think "rear brake accumulator" is a truer indication of what it's real purpose is...

I never figured out why the HA valves kicked in when you opened the door, though!

It's the "anti-jolt" system. Basically the idea is that if you open a door you're about to cause a weight change by loading or unloading the car, thus the suspension switches to soft mode so the pressure difference can equalize with the centre spheres. (Otherwise when you turned the key on there would be a sudden drop or jump in height when the centre spheres are connected)

The problem though is that although the electrovales get powered, unless there is enough reserve pressure at the accumulator the actual hydractive blocks wont switch into soft mode anyway, so this "feature" only works for a short time after the engine is turned off.

(Up to 10 minutes or so depending on how well your hydraulic system holds its pressure)

It's completely useless for when you come back to the car after an extended time and open the doors - yes the electrovalves come on, but it doesn't actually DO anything until after the motor is started and pressure has built up again anyway, so I'm not sure why they bothered...

(They could have put a timer in so that after 30 minutes of the engine being off it didn't bother to turn on the electrovalves with the doors...)

Regards,
Simon

citroenxm · Post by **citroenxm** » 19 Nov 2006, 12:56

Hi ALL!!!

Extreamilly interesting! To start with though, I did go under the car and disconnect the Rear Electro Valve, this however made NO difference at all - the car still sunk quickly. But however, I also changed the Two rear cylinder spheres too.

Lowered car, opened regulator, left car running for a moment for so then stopped it.

Now this is interesting.. The Drivers side sphere had NO Fluid pressure behind it, and spun off with little effort and little fluid loss, HOWEVER the passenger side one had ALL its pressure behind it, and when I removed it BOOOFFF my arm and area around the cylinder was all green!! There was still pressure there!!!!

So the next opinions on this?? I will try the Pressure reg screw release and see what happens with it.

Many thanks on this Guys!

Regards
citroenxm

Mandrake · Post by **Mandrake** » 19 Nov 2006, 18:40

Hi,

Not sure why there would be pressure on one side and not the other, but just a tip when depressurizing an anti-sink model - you need to set the height lever to minimum with the engine idling and WAIT at least 2 minutes (maybe even 3) before you open the bleed screw or turn the engine off.

The reason for this is it takes quite some time after the suspension appears to have stopped dropping before the pressure is all gone - there is still some 80 bars of pressure in the rear suspension after it has first dropped to the bump stops.

If you open the bleed screw too soon you cause both the anti-sink valve to close and the hydractive block to drop back to hard mode (centre sphere isolated) and once that happens any remaining pressure in the suspension is locked in place and can't escape, regardless of the height lever being at minimum.

For the rear suspension a handy trick to see if there is any pressure left is to grasp the rear strut spheres and wiggle them side to side (not too violently) and the sphere and the entire cylinder should rock from side to side about 10mm - if you can rock it around like this there is no pressure. If there is even a small amount of pressure, it will be rock solid and wont move.

I check they can wiggle like this BEFORE I turned the engine off and open the bleed screw. Unfortunately you can't do the wiggle test on the front suspension of a Xantia though, so you just have to take your chances there

Regards,
Simon