kevin2012

Recently, I had my 91 S4 PSD fluid flushed manually using the instructions online. It was not a difficult task to do and there was no problem at all except the soft hose has some wetness and the new hose is on its way to me from Roger.

After the flush, I even fired the solenoid valve many times (in pluses) to give it some workout.

Now, after this flush, whenever I switch the ignition key to position 2, I can hear the PSD relay clicks that I didn't hear before the flush at all.

Is this click normal? If it is normal, I guess the system needs to pressurize the PSD before the car actually starts. But will it also energize the solenoid valve as well? Otherwise, under daily normal city driving, the PSD will hardly have chance to activate and the solenoid will have great chance to seize.

Rob Edwards

The clicking is the high pressure pump building pressure in the accumulator, that's perfectly normal.

The only way to exercise the solenoid valve is to drive the car the way God and Ernst Fuhrman intended.

NoVector

Hi Rob - Are you saying your pump runs to rebuild pressure everytime you switch the ignition to position 2? That sounds like an acumulator not holding pressure.

To the OP, when you flushed was your fluid clear and free of bubbles? Just wondering if you may be sucking in air somewhere and it’s screwing up your pressure. I think your fluid would have a lot of bubbles when you bleed it if that was happening though. Just a thought... analogous to having air in the brake lines.

Rob Edwards

It does when it's been a couple of days to weeks since last starting the car, which unfortunately is most of the time these days. ( I honestly don't remember if it does it when the car's in regular use....) I was looking through the PSD folder on the Morehouse CDs, I'm not aware of a spec on how long the PSD should hold pressure- Any thoughts?

NoVector

Hi Rob - I wish I did. My original started acting like you describe--sometimes I would hear the pump run for ~5-10 seconds when I'd start the car. I sent it to Harold Stein to have it rebuilt and part of his bench testing was making sure the accumulator held pressure. But I don't know how long he measured it...

Anyway, I bought a spare unit and had him rebuild that one too and since it's been on the car, I don't hear that anymore. But I did notice that with my old one that everytime I'd flush it, there was always tons of little bubbles in the fluid. I could never get it "bubble free." Which made me think that might be part of my problem. I.e., somewhere I'm drawing air into the system.

Rob Edwards

I have an intermittent DIFF CONTROL warning that sometimes also takes out the speedometer on the GTS. And I'm pretty sure the ABS isn't working... But if I am out hooning around and break the rear tires loose the green PSD indicator will flash at me. Can't tell whether it's actually doing anything in terms of limiting wheelspin, though.

I now have a Theo tool so when I get the GTS out of storage I am hoping to spend some time trying to suss out the issues in the system. Maybe it's a defective PSD accumulator....

I have a spare PSD unit here (no idea whether it's any good, it came with the '91 GT trans I bought a while back), perhaps I'll hook it up to power and see what kind of pressure it'll generate. Anyone got a 3000 psi pressure gauge?

Here, hold my beer..

kevin2012

for my case, the old fluid changed out OK without any bubble but just a bit dark. I got no warning light and I think the PSD is working fine.
I hear the relay clicks once when I turn to poistion 2. I didn't hear the pump working as the system holds pressure well.
Again, I am more concering about the solenoid valve sieze because of lacking of use. I might hot wire a long cable to activate it from time to time from the trunk to avoid removing the rear wheel arch lining. Of course I will disconnect the wire from the PSD brain first.
Cheer

kevin2012

If sometime your speedometer also out, it might be the left front ABS sensor going bad because it responsible for sending signal to the speedometer and it affect the function of the PSD as well.Worth to take a look at it first.

Rob Edwards

That was the first thought when the speedometer went intermittent, I did some continuity testing in the harness (pins 48 and 50 at the ABS brain connector) for the front left sensor and it was fine, and replaced the sensor, which 'cured' it only for a short while.