exhaust/ fuel issue I am stumped!

Asked by Feb 02, 2013 at 01:09 PM about the 2003 Pontiac Grand Prix GT

Question type: Maintenance & Repair

2003 Grand Prix GT. It ran completely fine one day and the next I woke up to hard chugging and the
Catalytic Converter needing to be replaced and a blinking service engine light. The cat was
immediately replaced because that seemed like the obvious solution. All of the fluids look good and
clean. The chugging persisted and by the time i got home from the shop the cat was already glowing
hot again and none of the performance issues returned to normal. I''m currently treating it as a case of
bad fuel and draining, replacing, cleaning. However I really am not sure that this is the problem. The
code read simply, random misfires. Coil Pack? O2 sensor? I dont have the money to replace random
parts. Do any of you have experience with an issue like this?

10 Answers


start by looking for dirt on the mass airflow meter something like a piece of tree fluff may have got past the air filter and stuck on mass airflow meter and it cannot calculate airflow into engine of may be a leak in air intake system between filter and throttle body. if a coil pack failed 2 of the 6 cylinders would misfire as theres 3 coil packs not likely all would fail at once. any other issues usually don't just appear out of the blue like that. add some fuel additive/drier just for kicks as well incase theres water in fuel.

1 people found this helpful.

would agree with the above prognosis it sounds as if the ecu is not recieving the correct information from your air flow meter this is normally caused by debris/dirt build up get some carb cleaner/spray solvent and clean it carefully also clean the throttle body at the same time to remove carbon build up and that should do it regards j.s autos uk


does the exhaust smell like sulfur? is the temperature gauge not quite to operating temps? if these conditions are present, change your coolant thermostat, the engine is running cold. OR ... another reason could be a stuck fuel injector is dumping excessive fuel. listen to all fuel injectors while engine is running with a screwdriver. listen with your ear to the screwdriver for clicking. hope you find the problem.

1 people found this helpful.

also.. you might wanna inspect each sparkplug to see whick cylinder is causing the misfire. if it is wet with gas it must be investigated for ignition or injector trouble. you need to investigate which is collapsing your cat.


this car would know which cylinder it is he has a (multiple cylinder misfire) all of a sudden telling me it's not an injector or wire or coil all of which would cause misfire in only 1 or 2 cylinders not all of them.

1 people found this helpful.

Yes check each plug looking for individual misfire. If all plugs seem even look to O2 sensor. If you have anywhere close to 100k on vehicle I would replace O2 sensor.

1 people found this helpful.

It was the back panel of the coil pack. I had to take it in and run a full diagnostic on it i was stumped!! i should have known though i had one go out on a pontiac before. Thank you all for your input though i appreciate it!


Mine did that a couple of times because of corrosion. I got rid of all the rust and put dielectric grease to keep rust away.


had the same problem,it was a weak spark plug,and figuring it out put a dent in my pocket

Well I just put a new motor in my 2001 gtp and it's still run like shit so now I'm here and doing what you all have

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