c5 on the floor :(

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myglaren
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Post by myglaren » 13 May 2009, 17:39

cachaciero wrote:
myglaren wrote:It should only take about 1 minute to raise the car from minimum to maximum height.

Tailgate switch ONLY works with the engine off and only (I think, will check in a few minutes) if the car is normal height to begin with.
Nope! will work from low position checked that before writing it up :-)

Cachaciero
Yes, you are right, just been and tried it.

The car rises from minimum to maximum height in 40" and drops from maximum to minimum in the same amount of time.

cachaciero
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Post by cachaciero » 13 May 2009, 18:44

The following is really just some comments to the comments raised by DKAnders.

Motor fuse value, normally fuses are fitted to protect the wires that feed a device not to protect the device itself, however in this case the burn point of the wires and motor are probably very close :-(.

There was thread on this subject in another forum where a contributer claimed that:-
a: fuse failure was a very common problem on earlier Mk1's and that
b; Citroen garages routinely replaced the 50A fuse with a 60A and that the Mk2 actually had an 80A fuse, although I believe it may be a different pump motor on the Mk2 so probably doesn't count. I don't know if what was quoted was really as widespread as stated but IMHO increasing the fuse to 60A FOR THE PURPOSES OF TEST at least initially should be o.k will give few more seconds of run time which may usefull when troubleshooting.

For the motor to take enough current it must be doing work this implies either a very high pressure and low flow or hi flow and lower pressure. Now my instinct is that the pump could probably supply it's "short circuit" (hydraulic) max flow without exceeding it's max current rating, the hydraulic circuit load would be low resulting in increasing motor speed, motor current will fall for increasing speed.
The converse is true for supply into a dead end, the pump motor will operate close to stall with a corresponding increase in current draw.

So in this case my gut feel is that the motor runs for as long as it takes to raise the rear suspension after which both outlets are shut and it is driving into a dead end, the only hydraulic flow is any leakage around the electrovalves and pump elements.

For this to happen it has to be that one or both the height sensors are telling the controller that the suspension is not at the correct height, that the front or back or both are too low.

Of course it could be that the pump unit really does have a problem access to a Lexia would make troubleshooting this so much easier :-(

However for the moment assuming that the pump unit is good then the evidence is that the front height sensor is either shot or not set up correctly and is providing information to the pump that the suspension is too high, or there is a leak in front cylinder producing a total pump pressure high enough to get the tail up but not high enough to lift the heavier front. This seems the most likely scenario as if it was the height sensor then the moment the rear got to level the pump should shut off, it seeing the front as already being too high.

On this analysis I would suggest that Anders suggestion of checking return leak rate should be done on the front struts.

Cachaciero

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Post by myglaren » 13 May 2009, 19:12

Not sure that this has any bearing on cachaciero's last post but I have noticed that in general the front rises first, followed by the rear.

Loading doesn't appear to make any difference other than to slow the whole process slightly.

Front generally drops first too.

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Post by cachaciero » 13 May 2009, 19:24

myglaren wrote:Not sure that this has any bearing on cachaciero's last post but I have noticed that in general the front rises first, followed by the rear.

Loading doesn't appear to make any difference other than to slow the whole process slightly.

Front generally drops first too.
Neither am I :-) ... but it's interesting because I think mine is the same don't know if the controller in normal operation modulates the EV's to apply a bias to ensure level rising it could well do.

The only thing I am sure of the front is heavier than the rear of an unloaded estate.
Ergo the pressure in the front struts will be higher than the rear struts.

The pressure supply from the pump is common to both ergo the pump pressure has to be higher than the front strut pressure.

Cachaciero

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Post by AndersDK » 13 May 2009, 20:13

cachaciero wrote:The only thing I am sure of the front is heavier than the rear of an unloaded estate.
Agree ...
cachaciero wrote:Ergo the pressure in the front struts will be higher than the rear struts.
Dont agree.
The area of the front cylinder piston plus the attack point on the suspension arm is also adjusted to narrow the rear set up.
Front & rear requires approximately the same pressure to rise ...
cachaciero wrote:The pressure supply from the pump is common to both ergo the pump pressure has to be higher than the front strut pressure.
Always - as we would never get a lift then ...

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Post by cachaciero » 13 May 2009, 21:48

AndersDK wrote:
cachaciero wrote:The only thing I am sure of the front is heavier than the rear of an unloaded estate.
Agree ...
cachaciero wrote:Ergo the pressure in the front struts will be higher than the rear struts.
Dont agree.
The area of the front cylinder piston plus the attack point on the suspension arm is also adjusted to narrow the rear set up.
Front & rear requires approximately the same pressure to rise ...
cachaciero wrote:The pressure supply from the pump is common to both ergo the pump pressure has to be higher than the front strut pressure.
Always - as we would never get a lift then ...
Ah! good point, hadn't considered those mechanical factors.
So both struts require similar pressure to raise and based on a poll of 2 if anything the front will rise first which makes it harder to find a plausible reason to explain the scenario as it has been given to us, at this point I would tend to favour failure of the front suspension EV in the pump unit.

To prove it is not failed closed I suppose the next thing I would do is to disconnect the pipe to the front distribution block and see if oil came out when the pump was running.

Although if there was a double failure of both height sensors.... or possibly the supply to them?????? Trouble is the only way of checking those without substitution is with a Lexia.

Cachaciero

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Post by AndersDK » 13 May 2009, 22:38

Just had to re-read the complete thread as I felt I lost track on the original probelm :lol:

Right - this C5 was flat on its stomach.
It got up on rear when the fuse was replaced and the pump sprung into life - but still hangs on front.

Any external leaks from a burst pressure feed pipe would be evident ...

The front cylinders are of a similar construction like the XM & Xantia types, and these wont normally fail by large internal leak-offs.
But may do so of course.
Still this is also easy to test : unplug the leak-off hose from each front suspension cylinder in turn and observe if any leak-flow while the pump runs.
A few drops pr minute is perfectly normal, but nothing like a constant fluid flow.

I really dont think the front height sensor potiontiometer cold cause this problem, as it must at least signal back a low height information to keep the pump running thus burning out the fuse. It cannot prevent the front to rise, unless it signals back that height is already obtained, and that would shut off the pump, if the rear is at normal height.

This leaves us with the other possibility mentioned by Cachaciero : a defective front suspension circuit EV inside the hydraulic pump unit ... :cry:

It MAY help the EV springing into life - if the height setting is played with ...
I.e. try start the car with the height selector set at lowest setting.
Then select normal, high and low again etc.