Citroen XM Forum

That is what i thought , that it might be low pressure , i have no idea what the pressure should be in the system,
but if there is not enough pressure to open the valve on tickover , then there cannot be enough pressure in the system at low revs, i'm quite obviously no expert by a long way , but that must indicate low pressure from the pump maybe

It would be good to get to the bottom of it, to see if it could be reradicated ,

Could well be low pressure. It doesn't bother me, I can't see any other side effects from it.

Infact the SD when Ifirst got it had a "re-conditioned" FDV from the well known hydraulic specialist with an unspellable and unpronouncable name. It didn't hiss. But then again, the PAS didn't work either. So I was glad to have hissing and PAS when I fitted the FDV that was on the Onyx to the SD

Having today changes the accumaltor sphere today, it has made a differance in the suspension, it is much softer on the rear than it was, very much like my old Xantia felt,
And i thought that changing that sphere wouldn't / should not make any differance to the general feel of the suspension ,
but it has certainly made a differance, before there was very little movement in the rear when bounced, now i have approx 6'' of movement, which i'm told is about right.

Any thoughts !!!

May well be that there is enough pressure now for the hydractive valve to stay open.

Good point , Robert hadn't though of that one , il'l shut up , but thats worth thinking about !

Hi Harryjoe,the point to contemplate here is that the accumulator does not multiply pressure,it merely stores a volume of fluid under pressure as delivered by the pump and controlled by the regulator, excess pressurized fluid being diverted to the reservoir.When system demand requires, this stored pressurized fluid is admitted to the hyd system.If system pressure is low due worn/leaky components then the accumultor may never store any reserve, the regulator clicking constantly and the pump only keeping up with demand.The volume of fluid flowing through the suspension system is very small , again unless there are worn/leaky components,the steering requires the greatest fluid flow.The hissing of the fdv is normally associated with the steering pinion internal leakage.This is not necessarily a problem as the steering very rarely attains a pinion valve neutral position,as you can affirm by centering the steering wheel and applying light finger pressure left or right of centre and the hissing stops.The sudden improvement in the suspension is a query,but may simply be due to air in the system that you have subsequently bled.
robertm

Thanks Robert for that info,

It's strange that the suspension seems softer, if there is air in the system (which i thought i had got out ) , what is the correct proceedure for removing any air in the system ? , and il'l have another go tomorrow, asap, !!


Nigel

Hi Harryjoe,go to the self help files and take the link for PRIVATE CAR BOOKS, this contains all the procedures plus a wealth of other information.If you have access to the Service Citroen website it is also available there for free download.
robertm

Robert could be right about there being air in the system. You didn't say whether you opened the bleed valve before starting the engine, if not air will be pushed into the hydraulics by the pump.
The suspension will self bleed but the brakes wont.

To bleed the brakes run the engine and lightly depress the brake pedal. A stay trapped between the front of the drivers seat and the pedal, then move the seat forwards just enough works well.

You have to bleed the ABS first, then the rear brakes then the fronts. Make sure the suspension is set to high to maintain rear brake pressure.

robertmnorton wrote: The hissing of the fdv is normally associated with the steering pinion internal leakage.This is not necessarily a problem as the steering very rarely attains a pinion valve neutral position,as you can affirm by centering the steering wheel and applying light finger pressure left or right of centre and the hissing stops.
robertm

I tend to agree that it is rather a designed feature. I have a couple of schematics explaining the FDV and its relevant pressure regulator cooperation, and the former has 2 different paths to send the LHM depending on whether there's demand or not on the steering. Actually I might be wrong as I seem to remember there were not 2 but 4 possible functional combinations (states), not sure anymore. So I'm not sure it's the FDV or the pressure regulator making that hissing noise. The Diravi'd LHD 3lt XMs, like my V6, have the simple one-inlet/one-outlet/one return pressure regulator and they don't do such a noise.

But I wish Citroen had put some effort and got rid of the noise. Everybody asks when they enter my car "what's that noise?", "is it broken?"...

cheers
G