Air bubbles in the LHM gives harsh ride?

steelcityuk · Unread post by **steelcityuk** » 08 Jan 2007, 08:18

Guess what, it's riding soft again this morning. My take on it is this - the temperature on Saturday and Sunday (when it was harsh) was around 10 C but this morning it's only 4 C, so I think that because the weather's cooler the LHM is thicker and also the tolerances in the valves will be tighter due to metal shrinkage. I didn't have chance to check the cycle time of the regulator but I would guess that it has increased due to less leakage. Certain valves require a precision fit as opposed to using seals, the Doseur for example, this could be the reason for difference in ride from one day to the next.

Has anyone else noticed the ride changes with the weather?

Steve.

citronut · Unread post by **citronut** » 08 Jan 2007, 08:25

all hydaulic citroens ride is affected by the ambiant temperature,if its cold the nytrogen shrinks and if its hot expands,this usualy show up more if the spheres are a bit low on gas
regards malcolm

steelcityuk · Unread post by **steelcityuk** » 08 Jan 2007, 12:56

I see your point but the issue here is that Hydractive soft mode doesn't work when it's warmer but does when it's cold. The difference in ride is very noticeable. As explained elsewhere in this thread the spheres are 3 to 4 months old at most.

Steve.

bernie · Unread post by **bernie** » 08 Jan 2007, 19:42

Mandrake wrote:
So, bernie, have you done anything to your regulator thus far ? (Tested the pressure?) Out of all the things Steve has been doing the pressure regulator is the only thing I havn't already done...

Regards,
Simon

Apart from raining and blowing gales 29 hours a day, 9 days a week, I have'nt touched the car Simon. Just driven it feeling every dirt grain I go over but having the Citroen floaty feeling

Steve, I tested the internal leaks back to the main tank recently.
I disconnected all the pipes in turn, apart from main feed and return, and found zero fluid returning.
Also I've not noticed the weather making any difference to the ride, apart from driving through more puddles than normal

Mandrake · Unread post by **Mandrake** » 08 Jan 2007, 20:36

steelcityuk wrote: Has anyone else noticed the ride changes with the weather?

Steve.

Yep - mine usually rides well in cold weather and plays up mainly in hot weather.... although it seems to be as much the temperature in the engine bay as the outside ambient temperature - so on a cold morning it might ride well for a while but get worse after the engine bay has warmed up...

Regards,
Simon

Mandrake · Unread post by **Mandrake** » 08 Jan 2007, 20:38

citronut wrote:all hydaulic citroens ride is affected by the ambiant temperature,if its cold the nytrogen shrinks and if its hot expands,this usualy show up more if the spheres are a bit low on gas
regards malcolm

I always thought it was the change in oil viscocity affecting the amount of damping provided by the damping valves - cold vicious oil would give more damping and a firmer ride, hot oil would give a more floaty ride... but I guess theres no easy way to prove it.

But this is a fairly subtle change, the one we're discussing is a pretty blatent switch between good and bad ride.

Regards,
Simon

Mandrake · Unread post by **Mandrake** » 08 Jan 2007, 20:45

steelcityuk wrote:It couldn't last could it, the ride is hard again. However I notice that the cycle time of the regulator has gone back to 6 seconds. All I need to do is find the source of the internal leak. At least I know that all the valves and electrics work on the HA system and I know just how nice a Xantia can be.

Yeah frustrating aint it. Because my car rides perfectly some of the time (actually, most of the time now) I KNOW how good the ride can/should be, which makes the poor ride when it happens even more annoying. (The poor ride is still probably better than most conventionally sprung cars...)

I think you could be onto something there with the regulator cycle time - 6 seconds is just NOT normal. Even with a very leaky electrovalve mine was still 12 seconds... and I'd consider anything much less than 30 seconds suspect.

Finding it could be tricky though - you could narrow it down by examining the return flows to the tank from the various return pipes, but a lot of the smaller returns all merge together just before they reach the tank.

Regards,
Simon

steelcityuk · Unread post by **steelcityuk** » 08 Jan 2007, 21:41

Driving home from work tonight and the ride was harsh with the odd sudden softness at the back end that ended as soon as it started. I noted that the temperature was about 9 C which is pretty close to the weekends figure. I see what Simon is saying about the viscocity of the oil but I was thinking that if the slightly thicker oil and tighter tolerences lead to another few bars of pressure that could be all it needs to tip it into soft mode. In my Xantia it really is a night and day difference between the 2 modes. My journey to work takes only 12 minutes (give or take 2) so the engine barely has a chance to get up to temperature and so the warming of the fluid will be minimal I think. Maybe I should enquire how much the test kit is from Pleiades or start combing the scrappers for pipe work I can use to have made up for a standard gauge. I've seen this on Ebay which with the right adapters it would probably be a good way to go -

http://cgi.ebay.co.uk/Hydraulic-pressur ... dZViewItem

I thought that I may try disconnecting pipes at the various valves rather than at the tank, may take a little longer but I suppose you're in no doubt as to what is leaking. It's interesting to note that when the rear HA valve was assembled incorrectly the regulator time went up to over 7 minutes. My starting point will be the rear HC then rear HA valve.

What did you make of the XM postings?

Steve.

steelcityuk · Unread post by **steelcityuk** » 09 Jan 2007, 08:03

It was harsh again this morning, the regulator cycle time was 6 seconds give or take and it was 10/11 C. I'll know if it's temperature related if we get a cold snap.

Steve.

bernie · Unread post by **bernie** » 11 Jan 2007, 16:35

Has anyone approached Citroen HQ or a dealer about this problem?

steelcityuk · Unread post by **steelcityuk** » 07 Feb 2007, 15:27

Just as an update, the suspension kept changing between hard and soft but it was mostly hard. In the meantime I've swapped the springs around in the electrovalve at the front to give a constant soft ride until the light nights get here and I sort out a pressure gauge to try to trace the fault.

Steve.

steelcityuk · Unread post by **steelcityuk** » 15 Feb 2007, 21:50

As a quick 'fix' I've bought a new pair of front spheres for a non hydractive Xantia and stuck them on. At the rear I've drilled out an old pair that I had so that they are the same damper size as the non hydractive spheres. The ride is much nicer now and the cornering is still good. Best £40 I've spent so far. It'll be interesting to see what the ride's like when the weather turns cold and the hydractive works properly.

Steve.

DickieG · Unread post by **DickieG** » 02 Mar 2007, 22:49

I've been having a read through the Citroen Technical Training manual where in the Auto-Diagnostic chapter it states;
"If it is impossible to control the electrovalves (computer broken, electrovalve disconnected, supply voltage too low), the suspension is in the "firm" state hydraulically. On the other hand, for sensor faults, the suspension is maintained in the "supple" position.

Personally I've not heard of the second part of this statement, I'd always been led to believe that when a fault is detected the suspension went into "firm". Anyone heard of this before?

AndersDK · Unread post by **AndersDK** » 02 Mar 2007, 23:12

"... for sensor faults ..."

The sensors have nothing to do with the hydractive electrovalve(s).
Sensors provides drive condition inputs for the hydractive ECU to decide WHEN to activate the electrovalve(s).
If the ECU detects a known failure pattern (e.g. an intermittent disrupted sensor) then the ECU will replace that sensor signal with a default value. Then the ECU decides again as normal when to activate the valve(s). Of course this will happen on a slightly different pattern selection, as that one failing sensor value is now substituted by a failsafe constant value.

On the other hand : if a fault condition is detected on the valve coil(s) itself, the ECU will leave the valve(s) alone (de-activated), which pr design hydraulically will revert the valve(s) to the 'stiff' mode. This is to ensure you dont get a constant shifting between the 2 modes on any weird fault. That could be rather dangerous under certain driving conditions.
Note that early XM hydractive 1 systems have only one hydractive valve common for both front & rear axle.
With the introduction of the Xantia model, both Xantiae and XM's got the revised hydractive 2 system with a separate hydractive valve for both front and rear axles.

Mandrake · Unread post by **Mandrake** » 03 Mar 2007, 07:06

Anders is quite right - there are a number of possible "non-fatal" sensor faults that will still allow the car to spend most of its time in soft mode, but with reduced "functionality".

For example - the accelerator pedal sensor can be faulty which will prevent the car from switching briefly to hard mode when quickly applying and releasing the throttle - but it will still respond to road speed, cornering, braking, and so on...in fact I left my throttle sensor disconnected on purpose for a few months for this reason, with no ill effects - but if fault codes were read, no doubt a faulty throttle sensor would have been reported.

Other non fatal sensor faults include -

- Brake pressure switch - its only purpose is to switch to hard mode instantly under hard braking - if this sensor is faulty you just forfeit this feature - although acceleration is also deduced by the computer by rapidly decreasing measured road speed, which will also trigger a switch to hard mode. (But not as quickly as the pressure sensor, which is more or less instantaneous)

- Body movement sensor - it will switch to hard mode when there are very large sudden suspension movements, such as the suspension trying to bottom - if its not working, the suspension may bottom more easily on large dips, but otherwise things will be fine.

About the only two sensors that are essential are road speed, and steering wheel angle. If the road speed sensor is faulty then the computer assumes 100Km/hr all the time, the consequence being that even a very small steering wheel movement at low speeds will trigger a switch to hard mode, as if you were doing 100Km/hr.

If the steering wheel sensor is faulty you're likely to spend most of your time in hard mode as the computer can't figure out if you're cornering or not, and plays it safe...

The same Hydractive 2 training manual contains tables at the back of the book that state explicitly what the failsafe behavour is for every possible sensor malfunction.

Regards,
Simon