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jazzmaster, ASE Certified Technician
Category: Pontiac
Satisfied Customers: 2951
Experience:  ase certified
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1991 pontiac grand prix rough idle and stalls and engine

Customer Question

1991 pontiac grand prix rough idle and stalls and engine dies everytime throttle is used
Submitted: 1 year ago.
Category: Pontiac
Expert:  jazzmaster replied 1 year ago.

hi, can you clean out the throttle body with carb cleaner and see if that helps ,it might be full of gunk/deposits .

spray it while its warmed up.

see if that helps .sometimes the throttle body has to be removed to clean it better ..jazzmaster ..

Customer: replied 1 year ago.
The car is very hard to start and most times will not, if car starts it bearly gets to idle. will only run for maybe 5 mintues, then dies and always dies if you touch the throttle.
Customer: replied 1 year ago.
When it is running , it runs very rough like it is starving for fuel and a rich fuel suffer smell comes out the exhaust.
Expert:  jazzmaster replied 1 year ago.

does this have a lot of miles on the motor ? and lack of power ?

Expert:  jazzmaster replied 1 year ago.

I may be able to help you better with a phone call if you want

Customer: replied 1 year ago.
135,000 and the motor was running strong like a bat out of hell down the interstate til the other day when all this started, I pulled out to make a pass around 70 mph and the car just died and now it will barely start and dies everytime with throttle.
Expert:  jazzmaster replied 1 year ago.

ok, you need to do a compression check on all the cylinders .

the timing chain could have jumped .the compression should read at least 120 on each , if you have low compression or good compression on some and low on others the timing has most likely jumped a tooth or more ..jazzmaster ..

Customer: replied 1 year ago.
Already have my apologies for not stating that all checks good .
Expert:  jazzmaster replied 1 year ago.

have you taken the vacuum hose off the fuel pressure regulator to see if there is a presense of gas ?

Customer: replied 1 year ago.
No I have not but when it does run it runs at idol so I don't feel it's a gas problem but I will check those in the morning .
Expert:  jazzmaster replied 1 year ago.

ok, check that and check the spark as well.

I am not there so I have to go by what you tell me .

if it is hard starting it could be numerous things

also, what were the compression readings ?

Customer: replied 1 year ago.
They were anywhere between about 114 do 118
Expert:  jazzmaster replied 1 year ago.

that is kind of low and that will cause a motor to run bad/hard starting/lack of power and stalling .

that combined with how and when it gave you problems ,points to a jumped timing .

it can jump a tooth or two and still start and run(badly) .

I have seen this many ,many times over the years

the compression (normal) is around 180 .that would explain the problem you have ..jazzmaster ..

Customer: replied 1 year ago.
I truly have my doubts but I will verify tomorrow .
Expert:  jazzmaster replied 1 year ago.

A low copression motor will be harder to start/run rough/lack of power stalling -do you have these issues with it ?

Customer: replied 1 year ago.
Good morning, after the car sits overnight when the car is cold it will fire up and it will run at high idle and it will run for 30 minutes and run smooth and awesome, once it warms up it will not except throttle and it dies and it will not crank back up and until the car is completely cooled off which could be hours , even over night,I have change just about everything I'm going to change the ECM today. I have even changed ignition modules and that didn't fix it ,I need help and I'm very frustrated because if you look on the The Internet you see all kinds of forms and complaints about this problem with these cars from 91 all away up to 2006 and nobody has an answer but they can tell you to change $1000 worth of parts I don't understand someone has to know what's wrong with these cars there's too many complaints too many issues .
Expert:  jazzmaster replied 1 year ago.

I tried to get back to you ,the internet was out and I didn't get back online until now --sorry ..

so, ok,

when this doesn't start back up after being warmed up .have you checked the fuel pressure ?

the fuel pressure should read 55-60 psi when you firdst turn the key to run (not crank /start .

also, you need to check the spark to at least 2-3 cylinders and also the fuel injector pulse on at least 1-2 injectors using a noid light that plugs into the injector connector ..

I need to know what is missing of these 3 things and if there is a check engine light on when running please let me know if there are any codes stored in the pcm ,,thank you ...jazzmaster ..

Customer: replied 1 year ago.
Feul pressure is good I've changed out the ignition Coils and ignition module compression is good now the car won't even start when the car does run it runs for 20 minutes or so and then it's like somebody just turn the key off it does not run rough does not act like it's losing spark air is being blocked or Loss of fuel flow it's like someone just cuts the switch off the car just dies now the car will not restart it turns over I've got fire I've got fuel the air is not blocked but the car will not start is there a antitheft lock out on this car if so how do I reset it . Could my ignition switch in the steering column cause a problem it is loose and I can once the key is put in the slot I can rotate the plastic Tumblle by hand and if I rotate it slowly down on the air-conditioning controls the vent light will come on but there's no – indications are no dash lights if I rotate a little more than all the normal dash lights and everything comes on and then goes out like it's now in the accessory on position .
Expert:  jazzmaster replied 1 year ago.

if the switch was an issue I would think that you would not have spark .

try spraying carb cleaner into the throttle body and see if it tries to start then ..

p.s. usually if it is a fuel issue the car may sputter

when it shuts off like you turned the key off ,its electrical ,and the crank sensor comes to mind ,,as you have changed other components that show the same symptoms ..jazzmaster ..

can you wiggle the key when it runs and ,the car acts like it wants to shut off ?

Customer: replied 1 year ago.
I will change the crank sensor and hope I can get the car started the car has not started in over a day now I've been trying for hours and the car will not start if I get it running I will try to shake the ignition .
Expert:  jazzmaster replied 1 year ago.

please make sure that you are not getting spark to the spark plugs ,before changing anything .

also, if you have a tach/rpm gauge in the dash ,see if that shows movement when you crank over the motor .usually that is a good indication of a bad crank sensor and that combined with no spark and possible no injector pulse ...thank you ..jazzmaster ..

Customer: replied 1 year ago.
by crank sensor do you mean the crankshaft sensor that's the only part I can find and let me ask you a question would this cause all my problems because about a month ago before this started the serpentine belt broke going down the highway and it was tangled up in all the pulleys could it possibly have damage the connector when it came loose ?
Customer: replied 1 year ago.
I have fuel pressure I have spark and there's no air blockage every time I try to start the car it just won't start but when I'm turning it over I've got plenty of spark . Just need to know if that serpentine belt could've possibly damage that crank sensor and that could be causing my problems ?
Expert:  jazzmaster replied 1 year ago.

I have seen the belts rip at the wiring before and cause no start situations .

but usually there is no spark or injector pulse .

try to see if it starts with carb cleaner or tries to start or will start and stall may be an issue with no injector pulse ,if you have spark and fuel pressure ..

dont change the crank sensor(crankshaft sensor )

Customer: replied 1 year ago.
When I spray carb cleaner in throttle body, car tries to start. Injector pulse shows steady light with noid light connected, does not pulse off and on. Fuel pressure and ignition spark are all good . Replaced ECM, no help. I did noticed that when ignition key is first turned on the Service Engine Soon light blinks once, which is not normal. I have checked for codes and the only code I get is code 12. Checked spark plugs and they are in good shape and are not wet with fuel that might show a flood engine issue.
Expert:  jazzmaster replied 1 year ago.

will this still start and run when it sits for awhile still ?

Customer: replied 1 year ago.
No, car will not start. GM Pontiac Service Manuals states to check the resistance on all injectors, I am trying that this morning, a lot of work, but I am trying to follow the book. Nothing is helping with this car, actually it is worse, it atleast use to start and run for atleast 20 mins. after sitting over night. Now it will not run at all.
Expert:  jazzmaster replied 1 year ago.

ok, after you check the resistance on the injectors ,please let me know what the resistance was ..

Customer: replied 1 year ago.
If the resistance is off I will spend another $380.00 for injectors and then I will scrap this car if it does not run. That will put me at $1000.00 in parts that have not fixed this car, but made it worse.
Expert:  jazzmaster replied 1 year ago.

dont get any injectors .to check the resistance properly ,they all need to be disconnected

Customer: replied 1 year ago.
4 injectors read from 8.6 down to 1.3 ohms , only two read normal 12.4 ohms
Expert:  jazzmaster replied 1 year ago.

you have some lower resistance in some -any that are lower should be replaced .I have seen where a bad injector will take away from other injectors and even short out the others . you can hook them up one by one and see if the volts change as each is hooked up .as well /..