vsx suspension issues

[bradspau]

Hi all. I have a 1995 Xantia vsx with the hydractive suspension. Normally the car drives ok, but occasionally the front will go hard when I hit a large pothole or sometimes just during normal use. I can replicate the fault by braking just before a speed ramp, the suspension then firms up and the car crashes over the ramp rather than absorbing it. Is this normal?. I have replaced the center hydractive sphere, the rears and the fronts were done recently. I was told that the accumulator sphere could do with replacing as it is ticking. Would replacing the accumulator solve this ride quality issue as I understand it, the accumulator has no dampening properties ?


Any help/advice would be appreciated thanks.

[andmcit]

I'm expecting Jim and Richard (and others...) who've physically done this fix
to add more here as I've read into all of this but not actually done the repair
myself yet!!

The problem isn't hydraulic with the spheres but electrical with the front
electrovalve not working correctly; ie the switch that opens the middle sphere
in each axle sphere set up isn't working and effectively locking fluid in the
separate circuit. The fix is to renew the disabled diode in the trigger circuit
which in fact is available from e-crofting on ebay:

http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... 0265837179

although if you're a competent DIY'er you can fix this yourself. It's all covered
here on the forum if you search in past posts!!

Andrew

[RichardW]

Sounds to me like the front corner spheres are hard...which ones have been changed?

[pete_wood_uk]

But if you can hear it whistling, then it's OK, yes?

[bradspau]

front spheres were changed about 1 yr ago. suspension goes soft when car is running, hard when engine stopped, this is normal I believe. Can hear the electrovalves being energised when the ignition is in, etc

[pete_wood_uk]

Well I've always taken the view that if I can hear the valves, and if I can feel the difference between hard (ignition off for a while) and soft (engine running) then it's probably OK. Would be delighted to hear from others if there's a failure mode that can hide behind this.

One thing that you can try is some Citaerobics, if you haven't done any lately. It takes an age for me with my small pump (year 2000 car) but hopefully your 1995 car has the older pump and moves quicker. Give it 10 goes of full-up / full-down and see if that makes any difference, it sometimes does for me, I presume it's either air coming out or struts getting lubricated. When it goes up and down, does it go relatively smoothly or in a series of jerks...?

Pete

[bradspau]

Tried Citaerobics, although not that many times. Occasionally it will jerk at the front almost fully up, then settle. This normally only happens on first start in the morning after the car has been sat overnight. I recently lubricated the front struts, but it didnt seem to make much difference.

[CitroJim]

The Accumulator Sphere is critical to good Hydractive function. If it is causing the pressure regulator to tick at less than 30 second intervals then it is more or less flat and must be replaced. Normally, a good tick rate is measured in minutes.

The reason it is so critical is thus: The Hydracive electrovalves will only switch hydraulically if they have full system hydraulic pressure behind them from the accumulator. They cannot switch from hard to soft unless the main pressure can overcome the pressure being provided by the (isolated) Hydractive Centre Sphere can be overcome. In replacing the Hydracticve Centre Sphere, you may have made the problem worse as it's a 55 bar sphere as against the 62 bars of the main accumulator. Therefore if system pressure is low becuse the accumulator is flat and other bits of the system are making demands on what pressure there is, switching from hard mode to soft mode will be sluggish at best. Leaks or other pressure losses in the system can affect the hard/soft switching, as can the hydraulic parts of the electrovalves being duff.

It is normal for the Hydractive system to switch briefly on braking as you approach a speed bump and possibly as you put your foot down to powerr across it. If you observe the suspension doing its thing, it quite frequently switches briefly to hard mode although for the most part it spends its time in soft mode.

Have a look at this thread. It is Activa-centric but if you ignore the Activa bits, it'll give you all the information needed to give the suspension a good test.

If all that fails to resolve, go see someone with a Lexia and get the HA ECU read to see if there are any stored faults and any faulty sensors. The Steering Wheel Position Sennsor almost always records an intermittent fault.

[hirsty]

This definitely sounds familiar. I have replaced all 8 spheres on my Hydractive 2 last week and am not happy with the results. Having done major Citaerobics with no effect, this sounds as if it could be my problem. Unfortunately my hearing is impaired and I am unable to hear the valves. Do you suggest the diode repair would help ?

Keith

[CitroJim]

Do you suggest the diode repair would help ?

Indeed Keith, no harm in doing it even if the electrovalves are OK. It is a sort of insurance policy. If you can solder reasonably well, it's dead easy to do, else Roy's box of tricks is simplicity itself to fit.

Can you use an oscilloscope? You can use one to look at the waveforms to check the diodes are good and the right signals are going to the electrovalves. The waveforms will look spiky and distorted if the diodes in the electrovalves are bad.

On a good 'un you will see an initial 500mS pulse of 12V applied to initially operate the valve and then a 50:50 squarewave at around 1KHz to act as the holding current. The squarewave transitions should be clean and quick. bad diodes will give very ragged, slow transitions and the holding current will be insufficient to hold the valve operated.

[DickieG]

The easiest way to find out if the Hydractive blocks are switching electrically is to tune the radio to 171 LW, in soft mode you will hear a lot of interference which reduces significantly in firm (default) mode.

To get the ecu to react to vehicle inputs the car needs to have exceeded 6 mph once, then test the accelerator senor by moving the pedal quickly up or down should cause the ecu to switch to firm mode.

To test the body movement sensor drive over a dip/crest, not a corner.

Turn the steering sharply for the wheel sensor.

The brake sensor (only fitted to S1 models) only switches at maximum braking so testing that could work out expensive tyre wise

Whilst those example above test the electrical side of things you could still of course still have a leaky/sticky valve hydraulically.

[KevMayer]

Here's a pic of the diodes I added to my Activa to overcome the non operational electrovalve problems.



Kev

[Xaccers]

Here's a pic of the diodes I added to my Activa to overcome the non operational electrovalve problems.
Kev

Electrical insulation not really your thing?

[Mandrake]

Hi all. I have a 1995 Xantia vsx with the hydractive suspension. Normally the car drives ok, but occasionally the front will go hard when I hit a large pothole or sometimes just during normal use. I can replicate the fault by braking just before a speed ramp, the suspension then firms up and the car crashes over the ramp rather than absorbing it. Is this normal?.

Partly - yes it is normal.

The suspension will switch to the "hard" mode during hard braking, and in response to many other stimuli. One of the other things that will trigger a switch to hard mode is sudden large suspension movements, such as travelling over a speed hump too quickly, hitting a sudden large dip in the road, etc.

This is done by the "body movement sensor" which is attached to the front anti-sway bar.

It can be annoying in terms of making the ride a lot harder under certain specific conditions, I agree, but it is there for the good reason of preventing the suspension from bottoming - the suspension is so soft in the soft mode that if you were to hit a sudden large bump or dip the car would bottom the suspension quite severely - so this is to prevent that happening and control the rebound in a safe manner, the down side is the ride is momentarily harder.

Now, if your front strut spheres are low in gas, then when it switches to the hard mode, it may be a lot harder than it should be - because the centre hydractive sphere is switched out of circuit in this mode - only the corner spheres are active.

Edit: one more point, make sure you don't accidentally have the suspension set in the "sport mode" - orange light lit on the button just ahead of the height control lever, as this will make the car switch to hard mode a lot more often. Make sure that light is out if you are after ride comfort.

Regards,
Simon

[deian]

Just to add:

The suspension firming up on braking is a good thing, i think it is marketed by citroen at the time of xantia sales as anti-dive, it should work well as it will stop the back end from lifting too much and moving the weight onto the front causing instability.

Lots of sensors can feed the suspension ecu, but as jim mentioned, a healthy accumulator sphere is first port of call for diagnosing many hydractive suspesnion issues.

so to answer your question: yes it is normal, as long as you don't think it's too hard, in that case, replacing the strut spheres will help make for a more comfort drive over the policemen (that sleep).