[h2pmr]

i have a complete PSD assembly i removed many years ago and want to do a flush of it

using the excellent write up https://www.928intl.com/repair/psd1.pdf

opening the bleeder on the accumulator and then powering the pump i get no clear fluid out of the bleeder, its 50% foam / air bubbles that comes out.

is it doable off the car ?

or does the 4 pin pressure sensor? / regulator ? need to be powered or shorted ?

and looking at fig 4, powering the pump, i presume the earth is the brown wire in the fig so black is the 12v
cheers
Phil

[smiffypr]

You will need to get all air out of the system to get clear fluid out. You might need to operate the solenoid valve to bleed air from the outlet to the slave to clear the air. Black off the pump is positive, but be careful powering it direct as you could easily make it work against too high a pressure, I would say 5 seconds on, then release all pressure, or wire it up to be controlled by the pressure switch. To test it properly, you really need to have it wired up through the pressure switch so that you know someone can fit it and it work. When I did this many years ago, it was a typical part from a breaker, the harness was cut off, so I still had the wiring for the pressure switch.

[h2pmr]

thanks Smiffy, i think its a pump / prime issue, its as if there is no fluid in the pump to start with.
i now see there is a tip on Rogers site about using a mitivac on the bleeder to prime the pump circuit.
will give it a try and report back.
cheers
Phil

[worf]

... i presume the earth is the brown wire in the fig so black is the 12v

For 928s brown is always ground (31 Bus) and black is (99.9% of the time) ignition-on (15 Bus) power.

[h2pmr]

tried a mitivac, but still no fluid out of the bleeder
removed the reservoir, just to make sure the filter was not blocked and no allowing fluid in, but all was good
then i removed the metal H/P pipe from the pump housing and tried the pump, no fluid came out.
but blowing down the metal pipe with the bleeder open and air came out of the bleeder fine, so nothing blocked.

removed the pump, all clean and looked good, so i put the assembly on its nose and filled the pump housing with fluid, refitted pump and reservoir and worked the pump and sure enough fluid now came out of the H/P pipe hole.
refitted the H/P pipe and worked the pump and it now sounded like it was actually pumping something and not just spinning in air.
opened the bleeder and after a few seconds a nice flow of clean fluid was coming out
closed the bleeder and let the pump run for a few seconds.
then made a brake pipe to screw into the outlet hole to the slave and put a female union on the end
primed the pump for a few more seconds, removed the female union and powered the solenoid valve as per the bleed instructions and sure enough fluid was being forced out
so i am sure it was just a prime issue of the pump.
yes i know i should have taken some pictures but was doing it at my work as its a messy job and am not a fan of brake fluid, just seems to get everywhere, and forgot camera

and just a couple of questions:
doing it on the car you let the pump run until it cuts off, but i am just powering the pump with no ecu to tell it to cut off.
so roughly how long does it take for the pump to cut off after you close the bleeder ?

i had to slice the blue pipe off the reservoir, is it the same size as the clutch blue hose ?

cheers
Phil

[worf]

i had to slice the blue pipe off the reservoir, is it the same size as the clutch blue hose ?

Yes. But, the other end is a crimped-on hard line to a banjo.

doing it on the car you let the pump run until it cuts off, but i am just powering the pump with no ecu to tell it to cut off.
so roughly how long does it take for the pump to cut off after you close the bleeder ?

I'm pretty sure the ABS/PSD ECU doesn't tell the PSD accumulator pump to shut off. The pump continues to run until it reaches a specific pressure signaled by a sender in the PSD assembly. It's possible, I suppose that the ECU is in the middle of that control loop. A check of the wiring diagrams might be useful.

In answer to your question 4-5 to 10-ish seconds to pressurize the accumulator depending upon health of pump. The lock solenoid operates in fractional second bursts.

DO NOTE that the accumulator is at 180 BAR when fully pressurized and that the lock solenoid output can be as high as 60 BAR.

Treat the assembly as if it was a loaded gun when you have pressure in the accumulator.

[h2pmr]

thanks Dave, i have the connector that goes onto the 5 pin pressure switch and looking at the wiring diagram for it.

pin 1 is earth so i connect this to the earth of a battery
pin 4 is the earth supply to the PSD pump relay solenoid so i connect this to one side of a headlight bulb
i connect 12v to the other side of the headlight bulb
if i then power the pump it will run, build up pressure and bulb will switch off when up to pressure
bulb going out same as pump relay solenoid loosing its earth
just need to remember to de power the pump the moment the light goes out

should work ?

[worf]

thanks Dave, i have the connector that goes onto the 5 pin pressure switch and looking at the wiring diagram for it.

pin 1 is earth so i connect this to the earth of a battery
pin 4 is the earth supply to the PSD pump relay solenoid so i connect this to one side of a headlight bulb
i connect 12v to the other side of the headlight bulb
if i then power the pump it will run, build up pressure and bulb will switch off when up to pressure
bulb going out same as pump relay solenoid loosing its earth
just need to remember to de power the pump the moment the light goes out

should work ?

I have no idea, but your description sounds reasonable.

[worf]

I have no idea, but your description sounds reasonable.

I don't have the diagrams handy, what part does the relay (spare tire well) play in the circuit? Is it the relay that switches the pump and the pressure sender switches the relay?

[h2pmr]

I have no idea, but your description sounds reasonable.

I don't have the diagrams handy, what part does the relay (spare tire well) play in the circuit? Is it the relay that switches the pump and the pressure sender switches the relay?

yes thats the relay that powers the pump and is switched off by the pressure sender
will try it next weekend, and luckily there is enough spare length of blue hose to still fit on the hose with the metal crimped end, just need a new one on the feed to the pump which is just a push on at both ends
cheers
Phil

[h2pmr]

got the new blue hose on and bottle mounted, carried out the bleed procedure again, no air in the system, then connected a bulb up to the pressure sensor circuit.
brown wire to sensor going to a battery ground
brown / red wire to sensor going to one side of a headlight bulb
12v + going to the other side of the bulb and the bulb lights up
if it was connected to a car it would mean there is a circuit to energize the pump relay and pump would run.
when up to pressure the bulb should go out = the pump relay circuit would now be open and the pump would stop

i powered the pump and after 8-10 seconds the pump was slowing down, but light still on, a few more seconds later and pump nearly stopped, would not pump any more, but light still on
when give solenoid 12v and ground as to bleed the slave, there is a lot of pressure there, but no idea if enough to trip the switch.
so its either the pressure sensor, its not building up enough pressure or my bulb test system thats at fault.
need to try it on a 928 one day just to be sure but i think its the pressure sensor.
you can't win them all
cheers
Phil

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