Why won't car start?

20

Asked by Oct 01, 2016 at 07:29 AM about the 1992 Pontiac Grand Prix 2 Dr GT Coupe

Question type: Maintenance & Repair

3.4 DOHC (LQ1). Only 7000 miles! Running and driving fine. Stalled and
cannot restart. Towed to dealer. They said it has spark. Has fuel pressure and
good gas. Power to injectors but weak pulse. They said it needs injectors or
ECM. Wanted to remove air plenum for further diagnosis for 350 dollars. I was
uncomfortable with this approach and had it towed home. Car will start with
starting fluid and run for a few seconds. I bought what was hopefully a
working ECM from the salvage yard, installed and still no start. Many have
said timing belt on this car is common failure but even though it's old, it
appears to be in fine shape and I have to believe since it starts with starting
fluid and runs, the timing is fine. How do I diagnose this? I have no
automotive electronics knowledge. This car is very unfriendly to work on due
to lack of space. From what I see, getting to crank sensor is a major project.
Otherwise I would try one of those. There's gotta be a way to pinpoint the
issue without a hit or miss approach. Sure don't want to be towing the car
around town. I live in the Metro Detroit area. HELP!!

19 Answers

58,335

Sound,s like computer problem,ECM bad.

16,790

Is the check engine light on ?

20

Yes

20

When ignition key is turned on the service engine soon light is on. But isn't always in the on position?

16,790

Was the light on when the vehicle was running good?

16,790

Can you hear the fuel pump come on for a few seconds when the key is turned to the on position ?

20

Yes the fuel pump is running and I have pressure at the Schrader valve on the fuel rail. No the check engine light has never come on in 24 years. The car was purring like a kitten when it stalled.

20

This car has only been wet maybe once or twice in 24 years. Garage kept its entire life. Driven every year during nice weather for 24 years. All the wiring looks like it did when I bought it brand new. There are no modifications done to the car.

20

I have grounded the A and B terminals on the diagnostic connector and the service engine soon light flashes code 12. Don't know if when it stalled and I checked the fuses I cleared any codes or not. I did not notice the light when it stalled. I was to focused on getting it out of traffic. I was driving down infamous Woodward Avenue when it happened.

16,790

Well if it starts for a few seconds with starting fluid and it has good fuel pressure it has to be the ECM or bad fuel injectors so I am leaning more towards what T_S_T suggested.

1 out of 1 people think this is helpful.
20

I absolutely don't buy that all six injectors decided to go bad at once.

56,625

Code 12 means you're in diagnosis mode. If you have nothing else flashing out then there's no codes stored. When you replaced the ECM did you transfer the PROM from the original ECM to the new one? You have to do that. It's definitely a fuel problem since it'll run on starting fluid. You have to find out why you have a weak pulse signal to the injectors. If you give the dealer another shot at it tell them you want an older mechanic working on it. A 20 year old will have no idea of what he's looking at or looking for!! Personally I'd put the original ECM back in, with the original PROM and see why the injector pulse is weak. HTH. -Jim

1 out of 1 people think this is helpful.
20

This was a salvage ECM I bought. I figured I would take a shot because It had the exact same part number as mine so I if it was good and mine was bad it would fire. Well it didn't so I put mine back in. Do you think I should try to putting my prom in the salvage one I bought and try again?

1 out of 1 people think this is helpful.
56,625

Couldn't hurt. But with a salvage electronic unit you never know what you're getting. Since the service (part) number is the same it should work, if it's a good unit, with your original PROM. HTH. -Jim

1 out of 1 people think this is helpful.
20

I'm gonna try the salvage ECM tomorrow with my prom. I have nothing to lose. Js08016, do you believe the crank sensor is okay since it will start with starting fluid? Thank you for your interest! And by the way, the technician at the dealer was almost 60 years old! LOL!

1 out of 1 people think this is helpful.
56,625

I'd have to guess the crank sensor is good since you have spark and a weak injector pulse. With no injector pulse then I'd suspect the crank sensor. I'm surprised that an older tech couldn't diagnose the problem. If he's been around GMs for a number of years I'd think he'd be familiar with the older stuff too! HTH. -Jim

1 out of 1 people think this is helpful.
20

Is there anything in the intake sensor system that could cause this?

20

The car is fixed. It ended up being one shorted injector which in turn shut down all injector pulsing.

56,625

Awesome! Thanks for letting us know!! Very happy to hear that!! -Jim

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