1989 Grand Prix Stalls, Bogs Down

jz3 · 08-26-2007, 07:35 PM

My 1989 Grand Prix 3.1 has a problem that we can't figure out. Upon starting it idles for about 10-30 seconds then it stalls. It completely bogs down and stalls upon acceleration. No codes! Swapped out fuel regulator, MAP sensor and even the ECM. The TPI, O2, temp sensors, EGR, catalyst seem to be functioning properly. Good Compression. No vacuum leaks found. It is like it is starving for fuel but the pressure is good and constant (35-40). Any ideas? Your help is greatly appreciated!
95K Miles
Non-turbo

truck150 · 08-26-2007, 09:35 PM

it is either the mass air flow sensor or cat convertor plugged.

jz3 · 08-26-2007, 10:01 PM

Thank you for your reply. This vehicle does not have a MAF sensor. It has a MAT (temp) sensor in the air filter housing which checks out OK. It is not showing the same kind of hesitation you would see from a plugged cat converter.

richtazz · 08-27-2007, 05:26 AM

How old are your plugs and wires? Are you getting spark when the car dies? If not, it could be a CKPS (CranKshaft Position Sensor) or the wiring between it and the ICM.

jz3 · 08-27-2007, 12:33 PM

Wires are 6 months old. It is getting spark as it stalls. I can keep the engine going with starting fluid. Fuel pressure is good at the rail.

jz3 · 08-28-2007, 09:21 AM

Could someone kindly tell me what the correct fuel pressure should be?
Thanks.

richtazz · 08-28-2007, 10:00 AM

fuel pressure should be 41-44 psi key on/engine off, and should drop 3-7 psi with the engine idling and the vacuum hooked up to the regulator. It sounds to me like you have a shorting injector that is causing the injectors to shut off. I would take the upper plenum off and check the resistance in the injectors to see if one is way off from the rest. Then you can leave that injector unplugged, reassemble it real quick, and see if stays running then (it will be missing and only running on 5 cylinders , but it should stay running). If it stays running with the off injector unplugged, you need to replace that injector.

tblake · 08-28-2007, 10:23 AM

First i would start off by removing the o2 sensor from the exhaust manifold and then start the car to see if it runs any better. Doing this you allow an alternate path for exhaust gasses to excape and if it runs better without stalling probably safe bet that the cat coverter is plugged up.

I looked up your car in my database to find the fuel pressure spec but they dont seem to list it anymore?????? but 40psi seems about right, maybe a little low, but should be just fine. Does it hold pressure or just drop off once the pump stops running?

I learned something new when looking up your car though... In 1989 apparently the gp's came with a 3.1 v6 turbo. Is this accurate? I've never heard of it before. Was it a good system? Can the old Vin T 3.1 hold up to a turbo without blowing the bottom end?

tblake · 08-28-2007, 10:23 AM

rich, you beat me!!!!!!!!!!!!

richtazz · 08-28-2007, 10:47 AM

muhahahahaha, you're too slow T,

Yes, GM did offer the 3.1 turbo for a couple of years, 89-90 I believe. I had a buddy that had one with a 5-speed, and it was a pretty fun car. The older 3.1's bottom end is pretty sturdy, so as long as you keep boost levels within reason, they will accept a turbo with no dependibility issues.

In staying on thread topic, Tblake raises a good point as to checking exhaust back pressure, as the converter could be blocked and that would cause your symptoms.

jz3 · 08-29-2007, 08:35 AM

Problem solved. You were correct, a bad injector taking down all of them.
Thank you so much for your help!
Jon

tblake · 08-29-2007, 10:34 AM

Glad to hear the problem was resolved. Good Diagnosis Rich!!!!!!!!!!!!!!

richtazz · 08-29-2007, 02:41 PM

I get one right every once in a while,

. Thanks for the feedback JZ3. Not only do we like to hear our advice helped (it makes us feel all warm and fuzzy), but it could help someone else with a similar problem that may also read this thread.

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