PMIII pressure switch/accumulator

[Lee]

This question may not be about the pressure switch. My car had somewhat fixed itself so I had held off installing the new one. (history: pump was cycling/relieving due to overpressure) I intended to put it in before winter but now the PMIII has given me a new problem.

 

The other morning before work at start up the pump motor sounded different. (please excuse my sound effects.) Usually it sounds like a muffled eeeeerrrrt from behind the fire wall. Other morning, twice, it sounded more EEEEET, and right out of the dash cluster. It had quit the next time I hit the brakes 8 minutes later. All normal then.

 

Yesterday I did my front brakes. After the 40 pump depressure I found the rear resivior pretty low, front one fine. After doing the brakes and topping off both resiviors, it started it and the pump ran normal. Then pumping the brake caused that louder EEEET sound and the brake light flickered. Apon taking it for a round the block slow drive,using brake, it did the high pitch several times until the light just stayed on and I lost all power brakes. I checked under the hood and found that somewhere in the PMIII mess, there is a high pitched EEEET sound that cycles every 10 seconds or so. (update: this morning it wasn't cycling but did sound that way at power up and once more a minute later) This does not sound anything like the pressure relieving sound from last years pressure switch problem. I think it might be the accumulator..?? I checked fuses, they were fine.

 

What I have now is a stiff pedal that barely slows the car even in neutral.

The pump doesn't seem to run at all, not even at start up If you can think of anything please let me know. (update: at start up the pump seemed to run but not with normal sound, maybe it is the pressure switch acting up in a different way)

Thanks very much guys, past and present,

 

Lee

sorry for the colors and jumble. I tried to pm Chris A but I think the message got screwed up because it inded up in the outbox rather than the sentbox. So I put it on the board with updates.

[WhiteOut]

Bad news sir. Your PM3 system is toast. I had the same exact problem with my Trofeo, except that mine failed me getting off the freeway doing something like 80 mph. At any rate, the dealer said that I had had a small leak in the accumulator which caused the pump to work overtime and eventually burnt the pump out. As a result I had about a 1/2" of brake pedal travel and a brake system that absolutely refused to work. Total bill for repair, something like $1200 at the stealership (I didn't know any better, I was in high school at the time).

[GnatGoSplat]

Is it not possible to replace the pump motor and accumulator to fix it?

 

A PM3 that needs $1200 to replace would probably signal the end of life for any W-body old enough to have it.

[Lee]

Here's a thought. When I pumped down the pressure (40 pumps) I found the rear resivior low, real low. Maybe the sound I'd heard 2 days earlier was the accumulator getting air bound a little. Then the 40 pumps may have been enough to shove alot of air into the system. Enough for it to react badly upon startup and several more brake uses.

 

So....what is the effect of getting air into the system from a low fluid level?

 

Now for the moderator that felt he needed to move this out of the GP turbo forum to General.....What brake system does every single Turbo Grand Prix have? Answer PMIII. My question is for people knowledgeable on the PMIII. Where better to place a question about a PMIII?

 

Nuf said, yeah?

[buckethead]

I think that air in the system causes a squishy brake peddle, or one that travels all the way to the floor when stopping. That's remedied by bleeding the brakes. It sounds to me like you got a more serious problem than that.

[WhiteOut]

Is it not possible to replace the pump motor and accumulator to fix it?

 

A PM3 that needs $1200 to replace would probably signal the end of life for any W-body old enough to have it.

 

$1200 is what it cost me to replace the pump motor and accumulator on my Trofeo, and I believe that $800-900 was in parts. There doesn't seem to be any sort of aftermarket alternative available either, or at least there wasn't when I had mine fixed four years back or so. Your best hope is to find one in a junkyard, even then its pricey.

[bartonmd]

Not to thread hi-jack but...

 

What is the PM3 and does my '92 euro lumina have one?

 

Sounds like the power brake system that uses power steering pump instead of intake manifold vaccum? is that correct? If so, which models was it on?

 

THanks,

Mike

[White93z34]

Not to thread hi-jack but...

 

What is the PM3 and does my '92 euro lumina have one?

 

Sounds like the power brake system that uses power steering pump instead of intake manifold vaccum? is that correct? If so, which models was it on?

 

THanks,

Mike

 

 

your euro does not have the PMIII system, i think by 91 gm had redesigned the abs brake system.

[LukeZ34]

The PM III was the 89-91 GM ABS system. It was a fully electric braking system.

Not a bad setup, just a pain in the ass when it gets old.

[GnatGoSplat]

What is the PM3 and does my '92 euro lumina have one?

 

Luminas never got the PM3.

PM3 = PowerMaster III

It's the name for the ABS system they used in 88-91 Buick-Olds-Pontiac.

 

It's an extremely complex, overly complicated system using electric pump motors, nitrogen-charged accumulators, etc. Most foreign and domestic cars of that era that had an ABS option had something similar.

[bartonmd]

wow, that's one of those things that... well... blows when it gets old...

 

THanks for the info by the way!

 

Mike

[Guest Anonymous]

Now for the moderator that felt he needed to move this out of the GP turbo forum to General.....What brake system does every single Turbo Grand Prix have? Answer PMIII. My question is for people knowledgeable on the PMIII. Where better to place a question about a PMIII?

 

Nuf said, yeah?

 

 

PM me if you have a problem. The PM III is NOT TGP specific.

 

'Nuff said?

[WhiteOut]

PM3 was used through 92' in the Olds Trofeo and through 93' in the Buick Riviera.

[bryanjoseph]

A couple of weeks ago my PMIII's pump motor started to sound different and the brake light came on. However, it was just because of low fluid. Topping it up fixed the problem.

 

Are you sure you bled the brakes properly after working on them? The PMIII has to be bled using a special procedure. Perhaps air in the pump in the PMIII is making it sound weird.