90 Grand Prix stalling

[jim_haley]

Hello everyone, Im new so please bear with me.. I have a 90 Grand Prix 3.1 MPFI. When I start the car it will idle roughly for about 20 seconds and then stalls.. Normally it will not restart for several minutes just to stall again. I have changed plugs, wires, coils, Ignition Control Module, ECM, Map sensor, Crank sensor, new fuel pressure regulator, new fuel pump and clean supply line. It does not have a MAF sensor. Compression is 165 to 180psi and the fuel pressure is 47psi , cranking vacuum is 3 inches and idle vacuum is 14 inches. It has a new timing chain. I know that the alternator is bad but I didnt think that would cause the symptom. The car doesnt lose fuel pressure or electrical power anywhere that I can tell when it dies. So far I am stumped. Can anybody please give me an idea what to check next. I would pappreciate it. Thanks

[maxwedge]

Welcome to AF, any cel? Your vacuum is low number one, check that out possible leaks. Also possible egr valve is stuck part way open. Is this cold only, how does it run once you get it going, scan it and look at sensor inputs, if cold only, check coolant temp sensor also.

[jim_haley]

I exchanged the EGR valve and ohms tested as stated in Chiltons and both tested good, also the cts aslo tested good testing it in verying tempretures using an ohm meter. I searched up and down for vacuun leask and repaired all that I could find. Still the same problem. I cant get it to run long enough to reach normal operating tempreture. I ran a seld diagnostic and the computer sais the MAP sensor but wiltout the engine warm its not accurate but I replaced the MAP sensor anyway but still nothing changes.

[richtazz]

The MAP sensor vacuum feed is under the upper plenum. It goes from the vacuum block near the throttle body, under the plenum, and branches off to the PCV and MAP sensor. If you haven't taken the plenum off in your vacuum leak search, it's likely your issue.

[jim_haley]

I have replaces the upper intake gasket.. I checked the seal with starter fluid and a peice of hose.. Its air tight.. I know the vacuum is low but is it lo enough to stall the engine everytime at about 20 seconds? I appreciate the help

[richtazz]

quote "The car doesnt lose fuel pressure or electrical power anywhere that I can tell when it dies. So far I am stumped."

Have you tested for injector pulse, spark and fuel pressure readings right when the car dies? Loss of spark or injector pulse would indicate a bad ECM (or connection to it). I know you said you replaced the ECM, was it with a reman or used unit? Did you put your original prom chip in the replacement if you bought a used one(the same ECM is used on many different car/engine combinations so your original prom has to be switched to the new ECM)? If you bought a reman unit from A-1 Cardone, there is a good chance you got a bad one. They do a nice job on mechanical parts (axle shafts, brake calipers, master cylinders, etc...) but their reman electronics suck.

[jim_haley]

I watched the fuel pressure guage closely and it actually went up about 2 pounds as it died (which I believe is normal) and I bought the car as is and the guy before had bought used injectors and replaced them with no difference and I actually have 2 extra ECMs and I did use the same prom when I exchanged them. As far as the injector pulse width, I wish I had a scope to look at it but I dont. I do know they pulse because I listened to each one individually. I have good fire. I felt it personally (oops).

[michda]

Hello,

I have same problem with a 1997 GTP. Did you solve it?

[jim_haley]

No I still havnt figured it out but I am still working on it.. I am wanting to disconnect each injector one at a time to see if theres a change (kind of like a power balance test). Im just trying to decide on the best way to do that.

[richtazz]

I looked in my haynes manual, and it doesn't give the ohm spec for the injectors. I believe it's 1.2 to 1.6 ohms (on a 90 model with a 3.1), but I'm not 100% sure. If you start checking them, and one or more are way different, then there's a possibility they are bad. You can listen with a screwdriver against your ear and touching each injector to see if they are clicking (normally indicating that they are ok), but the injector rail is under the upper plenum on your engine Jim, so it isn't easy to gain access to them. The injectors are in the wide open on your car michda (once you remove the engine cover), so the screwdriver trick is easy to do.