Hydractive Problem

I dont really know if this is under the right heading as I think it may well be an electrical fault. But here goes. I had a suspicion the other day that my suspension was permanantly in hard mode, yesterday I checked it and found it was so. The reason I didn't notice it sooner was because with the 'comfort' spheres it still gives a tolerable ride. I have been trying to listen for the 'buzz and clonk' but because its been so windy here for the last few days I couldnt hear anything.
This morning after I got out of the car I could hear the front electrovalve clonking at regular intervals until it shut down, but nothing from the rear one.

I am wondering if this is related to my dropping the rear subframe a couple of weeks ago to repair a hydraulic pipe. Any suggestions?

Peter.N.

Hi Peter,

The electrical solenoid valve on the side of the main valve body is actually the part which Citroen call the electrovalve. The main body according to Citroen is a regulator. If I have a full regulator and associated electrovalve out in my hand and connect it to the power supply coming from an ecu then I can still hear a quite audible buzz because of the chopped waveform coming out of the ecu. Clearly it makes this noise whether its connected to hydraulics or not. So if you can get your ear close to the electrovalve to listen for the buzz that should eleminate the electrical side.

The clunk associated with the electrovalve may actually be the regulator block itself. In which case the clunk would be associated with the hydraulic operation of the block. If the buzz is present but the clunk missing then it may indeed point to a hydraulic issue.

Do you want to try the bit of diagnosis above first and try to identify if its mechanical or electrical? Once over that step we can drill down further on the right path.

Cheers

noz

This post has been edited by noz on March 01, 2008 02:08 pm

What do u mean exactly?? If we mean the same, this is only supposed to clonk once, when it shuts down.

cheers
G

Hi Noz and G

Thanks for the info but the whole thing seems to have been a red herring. I came home from the DIY store yesterday, got out, shut the doors the unloaded the the back, when I opened the front door again the car immediatly jumped up about 3" and I could hear the usual whining noise from the electro valves, but still no additional suspension movement. I can only conclude that the rear centre sphere has failed, which surprises me as I replaced them all when I bought the car just over 60k ago. The front doesn't seem to have a lot of movement either but the back has the hardest ride. I will try and get some spheres this week and let you know - when I have finished putting the bathroom together

Peter.N.

Is that 60 thousand miles? If so, it would seem time to replace ALL spheres

They are only about three years old and still clean! The corner ones are nice and bouncy (comfort spheres) but it appears that the centre rear one has suddenly lost pressure. I am sure they have lasted longer on other cars. I've got some centre ones coming tommorrow, so will see what happens when I fit them.

Peter.N.

The thot plickens! I have fitted a new centre rear sphere and the problem remains, there is no difference in suspension movement whether in hard or soft mode and yet the eletrovlave is definitly working.

This I proved on depressurising the system. I set the height to minimum, after it had settled I opened a door and the back rose a couple of inches and then dropped back, I repeated this several times over 10 minutes or so until there was no movement and found the centre sphere was completely depressurised, so much so that I was able to unscrew it by hand.

Could it be that the valve is opening and then closing again? I can still hear it whining.



Peter.N.

Hi Peter,

If my understanding of the system is correct, the only way you can be in hard mode when the car is stationary is with the ignition/engine off and the 2 minute timer has timed out. If the 2 minute timer has not yet timed out or the engine is running then it will remain permanently in soft mode. Therefore I have to conclude that the signal to your electrovalve(s) is(are) intermittent. The most obvious reason for the intermittent nature of the signal is overheating of the solid state relays in the suspension ecu. They have a thermal self-protection circuit which cuts them off if they overheat.

They overheat because the freewheel diode in the electrovalve is bust. The signal to the valves is a Pulse Width Modulated signal. I.e. it turns off and on at a given frequency (can't remember which frequency, lets say 100Hz). Every time the signal returns to zero (ie every 1/100 = 0.01seconds) the field in the electrovalve coil collapses and the induced emf keeps the current flowing in the original direction. Without the freewheel diode in the electrovalve coil to short it out the induced current returns back to the ecu and passes through the solid state relay heating it in the process. Eventually it overheats and switches off. If the freewheel diode is intact then the induced current simply circulates in the coil and is dissipated as heat in the coil. The coil is so large compared to the current that this small current isn't even detectable as heat.

I'm sure I recall you fitting diodes before but I may be wrong. Anyway....just my tuppence.

cheers

noz

FWIW my opinion is, for the reasons stated above, that anyone's suspension which "jumps", either up or down, at all, has the same problem as above. The way in which the ecu works always has the valves open at the right times and therefore the suspension should never jump.

This post has been edited by noz on March 06, 2008 08:38 pm

Hi Noz

I think the suspension was only jumping because I had emptied all the fluid from the corner spheres by setting the suspension on low, when I opened a door I assume that the valve opened and allowed the fluid stored in the centre sphere to momentarily increase the pressure in the corner spheres, that was bourne out by the fact that at first the centre sphere was tight and I could only unscrew it with the chain wrench. After I had opened the door several times, after the solonoid had stopped buzzing, and the car lifted slightly it stopped doing it and I could then unscrew the sphere by hand, it was completely depressurised.

Even though the centre sphere seems not to be in circuit I can still hear the electrovalve buzzing away merrily, it stops after the two minutes but starts again as soon as I open the door. Is it possibble for it to buzz and yet not be open? the front suspension seems to be behaving in exactly the same way.

I used to be able to feel a distinct difference in the suspension movement after the buzz stopped but now there is no difference.

Peter.

Yes. In case of mechanical failure, regulator clogged up, or insufficient hydraulic pressure.

It's 1000Hz.

Could it be there's a lack of pressure to activate the Hydractive valves?

Steve.

........and I could then unscrew the sphere by hand, it was completely depressurised.<<<<<<<

I think this remark is probably the most useful one I have read in these messages for a long time.
Makes the whole message worth while reading, as I have always found the removal of the centre sphere the most difficult of all, whatever tool you use, and here we have a method of removing all the pressure from it prior to hand removal.

On the line of "unsufficient hydraulic pressure",

I was re-reading the leak-post and I understand the piece you repaired was the one that feeds high pressure to the T-union that feeds the height corrector and the electrovalve?

If so, is it possible these pipes are (still) full of air so the high pressure to the hydractive valve gets "wasted" by the air compressing? If so, I guess a few ups/downs and a few more activations of the e-valve (eg by quick throttle openings) would pass the air past these elements. I have read some Xantias have a bleeding screw on their hydractive blocks, I guess it's for this job precisely. My '94XM doesn't though.

I understand you say the front is behaving OK, this would concur that this is not being a matter of central pressure reserve, but a "local" issue.

cheers
George

That's odd though, it shouldn't happen in theory: if you've put height correctors lever to lowest, all pressure should have gone, accumulator including. What pressure opens up the hydractive valves again and again up to 10 mins after? The rear middle sphere static pressure is about 40-50 bar, so there was residual pressure higher than that to push the hydractive valve open against whatever pressure was left in the middle sphere? Cannot figure out.

G