I have an entire PSD unit out and want to find the cause of the problem.
Diagnosis: PSD system was deactivated by the car and was run for faults and none were found on the Hammer. Per the WSM, when PSD is inactive and ABS is functioning and there are no fault codes, the problem lies in the "energy production" or the pump unit itself. I take energy production to mean the pump, accumulator, reservoir, and solenoid.
So I have the unit out. (See below) and want to bench test this. A couple things I noticed is that when I tried to flush the system per Louie and John's great write up, i attached the pump connector to the pump with the key in position 2 the pump didn't respond. I tried this a number of times and got no response from the pump. So initially i suspect the electric pump is the problem.
However, I know the pump wont work if the pressure switch (just above the pump) is faulty. There is a service procedure in the WSM to test this but it requires some special tool to do so, which I don't have.
Another thing to note, is that I had attempted to flush this unit before and looking through old posts of mine I see that I was unable to get any fluid out of the lock solenoid 2 years ago. However my post states that I was able to hear the pump run. So I am wondering if the pump really is the problem.
So in short I want to try and energize the electric pump to see if it works. So how do I do this? If I can get the pump to work, then I look at the next possible problem in the PSD line. That would be the pressure switch or lock solenoid. If the pump is simply DEAD then I guess I know what the solution involves.
Notes: The reservoir was filled with all kinds of junk. The inside has I guess a brake fluid varnish and is dark orange/brown colored and when the fluid is empty there is like a candied coating of the old old fluid inside. I imagine this crap is all throughout the system now and wonder if the lock solenoid can be taken apart and cleaned, maybe that's the problem.
What I want to try is to at least energize the pump itself so I can know that a) it in fact works or b) it doesn't and then I can move on to the next step.
To test the pump, can I put power from a battery to the 2 prongs
Any work undertaken on the PSD system can be dangerous due to the high pressure that can be generated, so ensure you personal safety at all times.
The PSD unit is interconnected to the ABS circuit, so to get it to operate whilst in the car you need to bridge out the relay in the spare wheel compartment, same way you bridge out the fuel pump (Terminal 30 & 87 IIRC-check before you do this otherwise you could damage the ABS/PSD control ECU).
Seeing that you have the PSD unit removed, to get the pump to run you need to supply a direct 12 volts DC source to the pump. To identify the polarity of the motor first check the color of the plug connector wires to the pump so as you can identify the positive and negative wires, negative wire should be brown (earth, prong #6) and positive should be black (prong #7) (1992 GTS). Prongs should be numbered.
I would suggest that your positive jumper wire has a two pole switch installed into it, so that you can control the operation of the pump - on/off as required.
Also check the pressure switches at the assembly. There's two of them. One at prongs 1 and 4, which should be closed at low pressure, and one two-way version, closed between 1 and 2, open between 1 and 3 (which reverses at max pressure, so open 1-2 and closed 1-3)
Before operating the pump I would clean out the reservoir and if you have a pressure bleeder I would try to flush the system through, however, as the pump is a direct displacement pump this type of low pressure bleeding may not work. To do this initial bleed, first remove the solenoid vent screw blue plastic dust cover (it sits on top of the solenoid valve and is clearly visible on the left hand side of you photograph), fit a clear plastic bleed hose over the vent screw and lead it to a collector bottle, slowly open up the vent bleed screw on the solenoid valve to bleed any brake fluid from the accumulator, remembering that the system operates at very high pressure (around 18 bar IIRC), because any high pressure spray can penetrate you skin or eyes, so wear safety goggles or a full face shield.
Once the basic flush is completed, if it can be done, fill the reservoir with new brake fluid, open up the vent bleed screw on the solenoid valve to bleed off any residual pressure from the accumulator, install your jumper leads to the pump connector using small female spade connectors and alligator clips to you battery or 12 volt power source, ensuring that the two pole switch is in the OFF position.
Now throw the switch and see whether the pump operates, if it does it will commence to pressure flush new brake fluid through the pump, into the accumulator and through solenoid valve and out the bleed screw into the collector bottle.
If this happens then keep running the pump until clean brake fluid comes out of the bleed hose, however, ensure that the brake fluid does not go below the lower level in the reservoir as you don't want to run the pump dry (high pressure pump with small clearances).
If this all works, I would then reinstall the pump back into the car, fill the reservoir up to the "full mark", bridge out the relay, connect the jumper leads between the pump female pump connector and the connector on the pump. Shut off the bleed screw. Turn the ignition on and then activate the the two pole switch and pump up the accumulator as per the instruction you have for bleed the system and verify that the pump will cut out on high pressure. If it does then the pump is OK, if not then the pump will probably be unserviceable.
This can he a dangerous procedure due the high pressure that can be generated, so this procedure is given in good faith, but no responsibility can be taken.
Tails 1990 928 S4 Auto (small additions by Theo)
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