1999 Pontiac Grand Prix SE - no start

I'm helping a young friend diagnose his 1999 Pontiac Grand Prix SE no-start condition over the phone. The problem arose gradually with stalling, and hard starting.

We've determined that it has spark and the fuel pump whirs when the key is turned on.

The EVAP vent valve has been replaced because a diagnostic check performed by a local mechanic showed that it was out of range. That didn't do the trick but it gave a minor boost to the economy, as such readings often do.

The same mechanic told him to suspect the MAF.

At this point, the engine will start when one side of the EVAP vent valve is disconnected, I assume it's the side between the valve and the intake, and die when it is reconnected. This tells me that the fuel mixture may be too rich.

One test that I was able to find for a no-start condition involving the MAF was to disconnect the wiring to it and try starting the engine:

[SOLVED] 1999 Grand Prix starts and dies instantly!
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This did not do the trick.

I will be going to where the car is located soon to see what I can see.

Any advice or tips?

Thanks, Jack

Reply to
Jack
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None of the parts mentioned displayed any signs of malfuntion.

Turns out that what my young friend called the "EVAP vent valve" referred to in the original post was in actuality the PVC valve.

Turns out the stalling only occurred at idle.

So the problems were hard starting and dying at idle.

Creating a manifold vacuum leak by disconnecting the the vacuum hoses to the brake booster and the PVC valve allowed the engine to be started and run at idle.

Given this, I reconnected the vacuum hoses to the brake booster and the PVC valve and held the throttle plate open a bit while the engine was cranked. It started up fine and idled great. The throttle plate stop screw was impossible to access and adjust so I bent a dime in half and forced it over the metal flange that contacts the throttle plate stop screw. The bent dime gripped the metal flange like a spring clamp. The engine liked this and so I added some Super Glue to help the dime stay in place. We called it a fix and my young friend paid me beer money for a week and a half and drove off to wherever. He reported back that the car drove fine, the idle speed stayed steady after warmup as read by the dash tach and he had no driveability complaints.

Coming back home, I got curious about what the real underlying problem might be and tracked down a component called an "Idle Air Control Valve" (I'm stuck in the Carburetor Age). I am pretty confident that this might very well be the cause of the behavior described above, but for now the bent dime seems to be doing the trick.

Reply to
Jack

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MAF and/or IAC would be my first guess. Blown out fuel pressure regulator next guess.

Reply to
Paul

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Fuel pressure regulator showed no signs of leaking gas out the vacuum port so I called that good. That was my first guess after hearing the symptoms over the phone, reading up on the system last night and before seeing the car today. I ruled out the MAF when disconnecting it did not allow the engine to start or to continue running after starting it by creating a vacuum leak and then closing the leak after startup. I am also making the assumption that a bad MAF would cause driveability problems and the car had none after the bent dime fix.

This seems to be a common problem with this system but there is hardly any mention of the IAC in the forums. Lot's of "My mechanic changed this, that and the other and it still does it! I'm out big bucks! HELP!"

The IAC is the cheapest of the components that might cause this problem and the easiest to replace.

Pontiac Grand Prix Starting / Stalling Issues

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Reply to
Jack

(snip) this, that and the other and it still does it! I'm out big bucks! HELP!"

The motor bearings tend to wear out or the passages and pintel get clogged with carbon. Its a square wave pulsed motor. You can check it with a 9v. battery. Its a pain to replace the IAC though so its your call to replace or repair.

Reply to
Paul

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