Hydraulic query - poss FDV but need advice

Aerodynamica · Post by **Aerodynamica** » Mon Nov 03, 2008 12:08 am

Hi all, this is a call out to those who've been there and had a similar fault.

Basically I found that the accumulator was dead so I replaced it (and ended up replacing a pipe too) and not the hydraulics are much better. There is still a problem tho.

It seems that there is some fault causing the HP pump to be under load for longer than usual - the PRV seems not to cut out at all.

The car will be ticking over, bonnet open in garage, steady idle and no untoward issues. I can sit on the front bumper and shortly after sinking under load the front suspension pumps back up accompanied by a loud 'PSHHHHH!' sound that doesn't stop after the suspension stops rising. In fact it just continues to do this quite loud continually unless I rev the motor where it comes to a stop with the familiar regulator click then it's just the engine you hear again.

The reason I think it's a fault is that the HP pump can be heard chattering under load as the 'PSHH' continues and it seems to labour the engine at idle. Only when you rev it to cause it to click to cut out does the engine idle settle to a steady normal tick over.

This issue was there before the accumulator was changed and remains after the change.

I'm thinking FDV valve for 2 reasons: 1. that of all my many Cits over the years I've never had a car that will not cut out until now and this is the first to have an FDV. 2. I read something similar about this elsewhere in BXC.

Has anyone got any thoughts?

The other possible issue is the pinion valve leaking through the pressure in excess and stopping the necessary amount reaching the pressure regulator.

Any experiences folks?

Debelix · Post by **Debelix** » Mon Nov 03, 2008 7:36 am

I've got the exact same problem in my car - experience?

So far changing the FDV didn't fix the "ssshhh"-ing sound and the car still needs revving up to stop the "shhh" and the pump ticking. Next thing scheduled for changing is the PR - i got a clean and good working one that i've got to change in upcoming days, so I'll tell you if it was the PR that is causing that kind of problem. If not... The next thing is the pinion ram and then... maybe the hidraulic pump, who knows...

...a-a-and I'm out of ideas

Aerodynamica · Post by **Aerodynamica** » Mon Nov 03, 2008 9:32 am

I'm sorry to hear that yo have the same problem! I don't think it's the pressure regulator because my car has low miles 48K, after changing the accumulator the suspension stays up for 2 days straight! after switching off the engine the accumulator is staying pressurized for hours! - my girlriend and I went on a walk up near Loch Lomond and afterparking up the BX we went off for a few hours walking, photos etc. upon return I noticed that after we got back into the BX besfore the engine was started the suspension had risen back up front and rear! - never had this kind of performance from any Citroen before!

If the pressure regulator was bad it would have an internal leak rate that was too high to sustain that kind of pressure. I'm sure it's not the regulator

I'm thinking HP pump or Pinion valve..

Aerodynamica · Post by **Aerodynamica** » Mon Nov 03, 2008 10:00 am

Also, I noticed on Sunday that it seems to diminish in its symptoms after a long run.

Debelix · Post by **Debelix** » Mon Nov 03, 2008 10:17 am

Hmmm, it seems that both of us have the same symptoms, but (maybe) different reasons for them. My BX takes only an hour or maybe two to be fully down, and it doesn't get up if pressed when the engine is off. That suggests to me that my problem comes from the PR.

In your case you might wanna' check the LHM leak of the pinion ram - big leak in it will cause the symptoms that you describe... If not the steering, it's possible to be the HP Pump, but if the problem was the pump, you would have notice it, because the car would rise very slowly and you'll have a fragmentary PAS?

Keep us updated please, I really wanna' know what's the reason for this "shhhsh" effect

mnde · Post by **mnde** » Mon Nov 03, 2008 1:24 pm

Me too with the ssshing cycle at idle, with the pump constantly on load, that only seems to break when you increase the revs slightly. Although I have to say it is a lot better since the dead accumulator was replaced.

(with a new XM centre sphere - following the experience of some on this forum).

It used to place a real burden on the engine when idling from a cold start - which didn't help, and I thought one of the main causes of stalling. I also used to find it sometimes (but not always) improved after a long run. When David fitted the new sphere, he also adjusted the cold throttle opening stop by half a turn, which means the cold idle is noticeably higher - and this has helped cold starts considerably.

Have you checked what your hot idle speed is?

Cheers,

Mark.

Aerodynamica · Post by **Aerodynamica** » Mon Nov 03, 2008 2:27 pm

Mark I didn't realise there were two different idle speeds!

It idles under 900rpm but this starts to drop when this hydraulic problem affects the pump.

I understand the XM S1 suffers from this too.

I think it's either the FDV or the pinion valve of the steering - it might be the FDV is working OK but is doing strange things due to a bad pinion valve but not sure. The steering seems to work OK.

I also traced the hissing sound to the pipe that exits the Pressure regulator and then joins a thick rubber hose. This feeds the 'cut out' flow from the PRV to the FDV.

My loose understanding having studied the diagrams of the system (think the link is on here somewhere) is that the FDV acts to give a continuous supply to the steering at 1/4 of the flow of the pump. The PRV will take the rest on cut in but when it cuts out it goes back into the FDV at the other end to give a second supply to the steering if the PRV is drinking too much of the HP pump inlet. One of the 2 valves in the FDV is balanced between the pressure coming in from the HP pump and the pressure coming out and the valve slides to proportion how much of the pump's input goes straight through to the PRV. This is why the PAS still operates with the engine running and with the PRV bleed screw loosened. If the cut out flow from the regultor and the HP pump input exceed the set level, there is a pressure release to dump the excess. This is caused by the steering having no demand say when the steering is straight. but usually the flow from the pump goes into the FDV, out again, into the PRV and out again, into the FDV and out to the pinion where it's either used or not.

I have observed that it's caused by the PRV not cutting out unless you rev the engine a bit. This never happens on any Citroen ever that doesn't use the FDV (please speak now if you know otherwise!)

Another observation was that when I loosened the bleed screw on the PRV, the hissing comes on perma style. If you then nip it up it continues until the rev fix. It makes me think there's a pressure loss at the regulator like having a bleed screw open - thing is, on mine there's absolutely no sign of loss in the regulator since it's staying pressurised for hours after turning off.

If it was caused by a leaking pinion valve then surely revving the engine would't work as the leaking would just start again shortly after. Mine only starts the silliness again after moving the steering a bit or making the suspension move up (basically a demand in pressure)

I have a gut feeling that it's a sticking piston in the FDV! or that the pinion valve is leaking fluid and making the FDV 'think' there's a demand and so more of the in flow is getting taken away from the PRV and so it never reaches cut out (until you rev a bit and the pressure surge is enough to overcome the leakage taken by the pinion valve)

Just thinking that last comment makes sense coz there's a flow metering jet in the FDV that divides the flow 1/4 to the steering valve and 3/4 to the PRV. Seems likely to me that the FDV prioritising valve should ALWAYS favour the PRV unless there's a demand from the pinion valve but since we're talking here about steering remaining untouched I do get a feeling it's a pressure leak to the steering that's causing this...

How can you confirm it though? I thought the return pipe from the steering valve was joined with some other returns making it difficult to say what's leaking most?

mnde · Post by **mnde** » Mon Nov 03, 2008 2:51 pm

Want to find out all about your carb?

http://www.rwbsmith.plus.com/citroen2/

and click on carburation > carb2.pdf

I think MK2 idle speed for a manual 16 is 850 ± 100rpm, not sure about MK1 but it should be in that document. My thinking is that setting it to the upper limit might force the PR to "click" in the same way as you applying the accelerator. I guess it would cover over whatever is the problem

I used to sit at traffic lights with the continous hiss and churning pump and press the accelerator very gently, noting at what RPM the cutout occurred.

Cheers,

Mark.

Aerodynamica · Post by **Aerodynamica** » Mon Nov 03, 2008 3:22 pm

Hmm, I do wonder, now I think of that too that the problem seems to be a build up of pressure not a loss of pressure like I was saying in the prev post. The HP pump seems to be doing lost of work until cut out of the PRV.

I should say that I note that it WILL stop the constant hiss without revving a bit if I left it idling for more than 5 mins.

I cant see how that could be the pinion valve as its leakage (if any) shouldn't 'just stop' should it? if anything as the fluid gets warmer it might even leak more.

I still think FDV.

The service kit for the FDV looks interesting as it replaces the filters and seals judging by the photo on here. is there any other part that gets attention such as the springs? could the slide valve springs get tired with age?

Aerodynamica · Post by **Aerodynamica** » Mon Nov 03, 2008 3:25 pm

had a check of the idle speed for mine - 650 rpm. I think this is what it was set to but it's hard to be certain as the tacho on the Mk1 is a bit vague at less than 900 rpm (there's no reading below it!!)

mnde · Post by **mnde** » Mon Nov 03, 2008 4:18 pm

I think you can get multimeters with a tachometer function that you can plug into the ignition module or something? I'm sure I've seen dial tachometers you can get for underbonnet tests anyway.

Mark.

jeremy · Post by **jeremy** » Mon Nov 03, 2008 4:32 pm

Mine has always hissed rather than click with this FDV and hasn't got any worse over the years. A touch of revs stops it and in fact as the MOT states that the test was done at 770 I think the idle may be a touch low. At least it all works and the light stays out which it did not do at one time!

Doesn't LHM always pass through the steering pinion valve when the steering is relaxed? Turn the wheel and the valve moves to cut off the bleed and the consequent rise in pressure in the pipe from the FDV makes the FDV valves move and supply more high pressure LHM to operate the ram?

tom · Post by **tom** » Mon Nov 03, 2008 6:40 pm

no comment

Aerodynamica · Post by **Aerodynamica** » Mon Nov 03, 2008 7:27 pm

Thanks for the help guys, Tom, the brake doseur performs oddly well, the car can last 2 days without sinking down at all! Compared to last week when I returned with the car, the rear end was slammed the next day. The leak rate is definately within limits - when the car is switched off there is still operating pressure several hours later - unless I'm mistaken I reckon that's a sure sign of a well sealed system.

I'll change the fluid , I have cleaned the filters and found them fairly clear. I don't think there is any milky foam happening in the tank but I'm going to double check that.

So given the relative health of the rest of the circuit, I just wonder what else could be the cause - I'm certain something's wrong. So the quest continues!

ellevie · Post by **ellevie** » Mon Nov 03, 2008 10:10 pm

Aerodynamica wrote:had a check of the idle speed for mine - 650 rpm. I think this is what it was set to but it's hard to be certain as the tacho on the Mk1 is a bit vague at less than 900 rpm (there's no reading below it!!)

Here's a fairly simple way to get a reasonably accurate estimate of the RPM without a tachometer.

1) Tune a radio between stations on the long or medium waveband and turn the volume up to hear the sparks.
2) Record this using your mobile or tape recorder etc.
3) Transfer the recording to your PC so the sound waveform can be displayed. The sound editor "Audacity" available free on SouceForge is suitable.
4) Count the number of spark peaks in a period of one second to give the spark frequency.
5) The RPM is then 30 times the spark frequency.

For example the recording shown below has a frequency of 32 sparks per second which equates to 960 RPM.