PM III questions (bad pressure switch)

[GnatGoSplat]

It seems the pressure switch in my PM III is no good. The pump won't stop running. I was told even with a completely dead accumulator, the pump should eventually build up enough pressure and stop running, so a bad pressure switch is the most likely cause. Is this correct?

 

How hard is it to stop the car with the pump fuse disconnected? I'm guessing these cars with no power brakes is almost impossible to stop, but does anyone have any experience?

 

What's the easiest way to get to the pressure switch and accumulator? I don't think I can even pull the heat shield without disconnecting the fuel lines. Do they need to come off? What else needs to come off to get access to these parts?

[Garrett Powered]

almost impossible, you gotta stand on it.

 

I am so glad I bought that SIA one for $350. good luck finding any parts for it. I have never seen anyone have luck piecing one of these together and have it be a reliable fix. I might have a pressure switch somewhere...

[mfewtrail]

Extended running or not shutting off at all can be caused by the pressure switch or the relay. I think I remember an old post from you where you might have fixed or replaced the relay? I would maybe try tapping on the relay lightly and see if that will eventually make the pump quit running(give it a minute or slightly longer). How long did you let the pump run?

 

When replacing the accumulator, I slaved the engine forward, removed the heat shield(fuel lines do not have to even be touched, I used a 1/4'' ratchet to remove the 10mm bolts holding the heat shield on), and then removed the accumulator. Since I used a prior replacement that was significantly larger than the OEM style units, I removed the throttle body to make room for the larger accumulator. If you have a way of slaving the engine forward slightly further than the dogbone bolts(like w/ a lisle or homemade engine tilter), I'm sure you could get one of the larger accumulators in there without having to remove the throttle body. With the accumulator out of the way, I believe you should have plenty of room to remove the pressure switch. You're going to need a fairly large deep well socket to remove the pressure switch, I think it's 38mm(1.5'' in works fine) in size.

 

If you don't have a service manual for the car and want some info, troubleshooting charts, or whatever, just let me know Shawn. EDIT: I came across this a few minutes ago in a search: http://arrc.epnet.com/autoapp/8800/8800.htm - PMIII repair info, etc. is already hosted there along with other stuff for these cars.

Edited October 26, 2010 by mfewtrail

[GnatGoSplat]

Thanks Matt! The pump runs 10+ minutes for sure. I tried not to run it real long, but I was futzing around trying to get codes out of the EBCM and I'm sure doing that, the pump may have run for at least 10mins or so.

 

I do have the service manual, but it didn't specifically mention whether I need to pull fuel lines, TB or not, I don't think it mentioned tilting the engine, so all that info is very helpful.

 

Do I need to plug the pressure switch and accumulator holes if I pull them (constant spewage, or no?), and how much fluid can I expect to lose?

[mfewtrail]

Do I need to plug the pressure switch and accumulator holes if I pull them (constant spewage, or no?), and how much fluid can I expect to lose?

 

I only had my accumulator off of my car for a few seconds and don't recall it dripping much at all. I removed the old one and slapped the new one on figuring doing it quickly would minimize the air entering the system. I'm sure both will drip at least for a short period of time after being removed. I would try to stuff a shop towel or maybe some of those blue shop style paper towels in the holes along with trying to rig up some sort of catch pan below the PMIII(maybe a cut up milk jug, 2 liter soda bottle, or something that you can cram back there to catch stray drips). The rear housing that the accumulator and pressure switch screw into has some type of valve in it IIRC, so that might keep it from leaking a lot, but I'm really not certain about that.

[GnatGoSplat]

Thanks, Matt! I'll pull it and try to clean it. There's a Lotus Esprit guy says he was able to fix his pressure switch by cleaning it. Considering you can't even buy them any more, it's worth a shot.

[mfewtrail]

Did you have any luck w/ cleaning the pressure switch Shawn?

[GnatGoSplat]

Not yet, I haven't found a socket yet that can pull it. Would a 38mm hub socket work, or is that going to be too long? I've been thinking I might need to get the Kent-Moore socket because clearance seems pretty tight.

[mfewtrail]

Not yet, I haven't found a socket yet that can pull it. Would a 38mm hub socket work, or is that going to be too long? I've been thinking I might need to get the Kent-Moore socket because clearance seems pretty tight.

 

A hub socket might work....if it's thin enough. I've only removed a pressure switch from a PMIII unit that was off-car. Considering kent moore makes a socket for this purpose, it might be needed. Looking at that socket, it appears to be thinner than most of that size. I'm not sure if it's 100% necessary for removal or that Kent Moore produced it so that the pressure switch could be removed w/o removing other components.

[GnatGoSplat]

Yeah, I think length may be an issue. A hub socket will need an additional 1-1/2" or so behind the socket for the wrench, and the tranny is awful close, even with the engine rotated. I really don't think it will fit. The Kent-Moore socket will accept both a ratchet wrench and it has a hex end to accept an open end wrench as well.

 

I did find a completed one on eBay that was $25+s&h and they relisted it for $3 more. Ugh, when you list something and it doesn't sell, aren't you supposed to reduce the price? I offered them $20.

[GnatGoSplat]

Okay, I picked up a J-37117 for $30 and it fits with my fancy 3/8" ratchet that has a pivoting handle, but just barely. I got the thing out and tried cleaning it with brake parts cleaner, etc. None of it seemed to do anything. Then I soaked the end of it with lacquer thinner and that made whatever tiny silver piston is in the pressure switch become movable. I pushed it in with the end of a paperclip, then banged it on a piece of wood to make the piston come out closer to the hole and repeated about 50-times like the Lotus Esprit guy did. I reinstalled it, but wasn't able to get it nearly as tight as it was installed before. Hand tight is the best I could do, and no way I could ever get a torque wrench to fit in there. I did the 3 quick presses mentioned for the accumulator bleed procedure, and the pump kept running. This time I checked the brake fluid, and WTF! Not just low, but REAL low! That was really unexpected, because I'd checked all fluid levels before parking the car and they were fine. Anyway, I filled it up and now the pump stops after 40 seconds. D'OH! I'm an idiot, I went through all this trouble for nothing!!! Ugh, it didn't occur to me it could lose that much fluid just sitting (where it went is a mystery).

 

It's still not right because it runs every time the brake pedal is pressed (like it used to), but the fact it shuts off tells me the pressure switch is probably okay. Well, maybe it isn't, but I tried cleaning it and the only thing I can try next is an accumulator unless I can find a J-37118 tool to test the pressure.

[mfewtrail]

That's odd if it's low and you can find no leaks. Have you looked at the rear of the car near the proportioning valve to see if it's leaking?

[GnatGoSplat]

Yeah, proportioning valve was dry. I even took pics when I had the tank out. The only thing I can think of is maybe the diaphragm in the accumulator ruptured allowing the nitrogen chamber to fill with brake fluid. I don't know if that's even possible, but it's all I can think of. I did happen to find an extra EGR filter wedged down by the down-pipe while I was messing with the pressure switch. I guess someone knocked it off years ago.

[GnatGoSplat]

I bought a new accumulator from Amazon and installed it. Super easy, but now the pump runs every other press of the pedal on a firm press, and every 3rd press about halfway down. Is this normal? I thought I read somewhere the pump should only run every 5-6 presses.

 

Is there anything else I should bleed? I just did the accumulator bleed (3-firm presses) and the solenoid bleed.

[GOT2B GM]

I would be happy it works as well as it does, both my PM3 cars I've had / have were no better (even after a new accumulator)

[White93z34]

every 2-3 normal presses should be about normal.

[GnatGoSplat]

Thanks guys, I guess if that's considered normal, I'll check this job off my list!

[White93z34]

Nothing about PMIII is really "normal"