Prior PMIII: Pump runs every pedal push

[LukeZ34]

Chris A's site says a properly maintained PM III will run every 2-3 pedal pushes.
The Prior PMIII in our TGP runs every time you push the pedal.
This has been happening for quite sometime, and I just thought it was caused by air in the lines/master cylinder. I changed 2 rear calipers long ago, and never needed to bleed the lines. (Filled calipers w/ fluid, and didn't let brake lines drip) After a while this lead to spongy brakes, and just overall crappy performance.

I bled each caliper, and the 2 master cylinder ports today hoping that would cure some braking issue's we've had lately.
The car brakes MUCH better after bleeding everything, but the pump still runs at every push of the pedal. What else could be causing this?

[Prospeeder]

No lights on? I belive the Pressure switch could be faulty and think the fluid pressure is low and allow the pump to run constantly

[GangstGP]

I got the prior and it does the same thing. lucky it stopped leaking after the first few weeks, otherwise it would run the pump constantly. not to mention a high pitched squeaking sound that sounds like when you pinch the end of a baloon off.

I e-mailed them a few times before they would even respond. but they offered no advise on what to do. but it still runs every push of the pedal and it feels a little more spongy than a factory unit but it works I guess. :?

[Prospeeder]

3 year/30k warrenty on them correct? Send the fucker back!

[R Dubya]

typically if the PMIII runs every push of the pedal, the pressure switch is bad or the accumulator is not keeping the proper psi.  You should have 2 or 3 pedal presses before it cycles.  Do you have a spare accumulator to check?  Still within warranty?

[TGPilot]

Sounds like the accumulator. My TSTE does that and I have tested the pressure switch.

Could be the pressure switch...but the accumulator is what stores the pressure between the pumps of the pedal... 8)

[GangstGP]

doesnt the prior ones come with brand new accumulaters for a thousand bucks? I thought something was wrong here. I guess I will have to swap in a different accum. not something I am looking foward to doing but I would rather be safe.

[LukeZ34]

It's over 3 years old, I know that. Probably more around 5 years old.
I've got a spare (new) GM accumulator sitting in a parts box here. I guess it wouldn't be such a bad idea to give that a try.
The unit does have the Prior accumulator on it. I'm just confused that it would be having problems already.
Do you have to bleed the MC after swapping the accumulator?

[Invasion1]

<----------------Glad he has no ABS PMIII  :wink:

[Tooky]

GangstGP, My TGP did that, and you very accurately described the "noise" it makes when it overpressurizes!!!   :D (pinching a balloon, LOL)

Mine would even run when the car was shut off and I would have to "hit" the relay next to the positive battery terminal / fuel pump relay area.  Then it would stop.

I had to do two things (if I remember right), one was a new relay, and the other was the pressure switch which was UNGODLY expensive for a fucking pressure switch!  It was something like $280 from GM.

[R Dubya]

yeah luke you do have to bleed the system after changing the acc.  IIRC you only have to do the unit itself, but it probably wouldn't hurt to just flush the whole system put all new fluid in, lines, calipers and all.

[LukeZ34]

It's already got new fluid in everything as I flushed everything this past weekend.
I can do the MC again though, that was simple to do. Thanks for the help, I'll swap the accumulators out this weekend and post the results. As long as accumulators don't go bad from sitting around for a few years, this should fix everything up again.

[GangstGP]

OK mine used to do that sound, but it stopped. and I noticed yesterday when I was sitting in the car it was switching on every 2-3 presses. so maybe the thing is starting to break in or fix itself. very strange.

I guess there was some pressure that cleared out of there or something.

The pump ran every pedal press for the longest time though I remember. but then again, I have been bleeding the brakes and untangling all the wires and heat shielding. my guess is the heat got to it and the pressure was too much.

I do need to look into relays because most of mine are still stock.

[pontiac6ksteawd]

Let me know if the ACC fixes the prob for you. Mine is also doing this. I am planning on bleeding out the entire brake system next weekend, and probly need to order a ACC for it befor I do that.

Is there a FAQ about bleeding the PMIII? I already know how to do the cals... :lol:

[LukeZ34]

I'll let you know how it goes.

Bleeding procedure:
http://www.tpsgarage.com/TGP/brakes/powermaster.htm#BLEEDING