Happy New Year to one and all.

Something I've noticed recently. After the car has been on its highest suspension setting for any length of time (like a couple of minutes) there is a massive jerk just after I reset suspension to the ride height setting. I've had two suggestions as to the cause: sticky height correctors or an ECU fault. My first instinct was that it was height correctors but then it occurred to me that the jerking started after I fitted Mr Mackay's box of tricks to the ECU.

I've checked the electrical connections between the box of tricks and the ECU and all seems to be fine. Any thoughts?

Jamie

Hi Jamie,

Ive just been out to try this with my Xm, as that also has the box of tricks fitted, but after letting it stand in high for 10 minutes, letting it back to normal ride height again just sinks slowly to the normal height, no jerking.

Id say its more a sticking height corrector than the ECU.

Chris

Is it a jerk as in uneven movement, or is it a violent drop?

Jerking could be anything from sticky struts, seized height corrector. Sudden drops / jumps are to do with the electrovalves opening / closing the middle spheres with negative pressure in them, and is usually caused by electrovalve, ECU, or sensor problems.

Ciarán

..............or air in the system, if its been worked on anytime recently and many up and downs where not done air could still be in there, otherwise it will be as others have said your E/V opening with + or - pressure in the centre sphere.

D

Thanks everyone for the answers.

Thinking about it, the jerk I described is quite violent, and it doesn't happen every time I do Citroenaerobics - only when the car has been standing on "high".

This is pointing towards the ECU/spheres or air in the system, I think. if I'm right and this is connected with fitting the box of tricks, then it might be the case that the valve was stuck shut previously and bow it's open, I'm getting this effect.

Ciaran, if there is negative pressure in the centre sphere, does that mean it's flat?


Jamie

Since Ciaran aint here...............................it doesnt mean the sphere is flat, if the Electrovalve is shut the centre spheres are no longer connected to the suspension circuit, so if the valve closes at full suspension height it holds the pressure that was in the circuit at that moment, it stays shut as the suspension lowers and the pressure in the system drops, then for some reason after the suspension has dropped or on its way down the valve opens and pressure suddenly rushes out of the centre sphere to equalise with the now lower suspension circuit pressure causing the car to jump up. This can also happen in reverse causing the car to drop. The thing is whenever the car is stationary with the engine running it should always be in soft mode (Electovalve open) to stop this unequal pressurisation occurring, this is why also the car will switch to soft when the doors are opened when the engine is off so that as you load/unload the car system pressure remains equal. If you think the EV's or more likely the controlling ecu are working correctly it could be sticky struts, air or one of the other suggestions.

Good luck with it

D

I'll bleed the system and then see what happens as that seems to be the simplest first step.

If it is the ECU, EV problem, then it seems to be caused by sudden opening and closing of the valve. I'll check to see if the car jumps up or down!

Many thanks

Jamie

this got fixed on mine with a new (2nd hand) strut.

it had been doing it for a while but finally when the wheel was off and the hub moved v.violently upwards i figured it was time to sort it - i'm just glad my head wasnt in there looking at something.

just to add some clairty... a sticky strut will not show up initially when raising the car because of the gradual nature of the change in forces, but when lowering the car it is easy to build up gravitational energy by the strut sticking and holding the car up. Then when gravity forces overtake the strut friction its a sudden drop.
Thats at onset of sticky strut.
but eventually on my car it got so bad that even raising the car would cause a sudden movement.

Gav

Was it just on one side, then? And did this seem like a two-sided problem before you diagnosed the problem?

J

Dean has pretty much summed up the rhyme and reason behind the valve / middle sphere issue.

My moneys also on this being the problem, but the cause could be a multitude of things, from pressure issues, to the age old ECU / EV diodes problem (e.g the valve can't stay open for extended periods of time so cloese prematurely despite the ECU's intentions.
This is a fairly common one, just trying to find some links to similar threads.
I believe Peter recently had this problem with the diodes on one of his estates and fixed it.

Be careful with triggering the jerking action BTW, the violent movement and changes in pressure (particularly in the case of a drop), can rupture sphere membranes and damage strut mounts etc...

P.S On the subject of suspension etc, it might be worth dismantling and cleaning out your front height corrector, just to rule out any slow reaction issues. Mine was done last night, and now any rising / dropping is smooth and instant, it took a few seconds to react before

jamieb, in my case it was just one side, the nearside. Never any indication from the offside of any problem.

When i first noticed it, i simply ignored it or just did some robotics in the thought of clearing out debris. But it just got worse with time.

I'm sure cleaning out the height correctors would be a good idea. Haynes is quiet on the subject . Where does the front one live?

In general I'm leaning towards the hydraulic theory, just because the problem started after I fitted the diode replacement box. In other words, I suspect that by curing the diode problem, I've uncovered another.

Thanks for the advice, everyone

J

A simple way to rule out the electronics is to disconnect the ECU, which will put the system in permanent hard mode. If the jerk still happens with the ECU offline (and hence, the valves closed and centre spheres isolated), then you have a hydraulic / strut problem. If not, then its the electronics.

I still think its going to be electrical TBH, but that simple test may rule some stuff out.

Ciarán

I would never have thought of that. Ta

J

Anyone has pictures or instructions how to clean the height correctors?

thanks in advance
Caique