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Questions and Answers

Grand Prix Misfire

Q. My 1996 Pontiac Grand Prix 3.1, 6 cylinder, ABS, auto (now 84,000 miles) has a problem not solved with last advice. When you accelerate 45-70 mph you can feel engine misfiring & service engine soon light comes on. The hand held computer diagnosis says code 300 (which is #3 misfiring) sometimes it says multiple misfiring.

I've changed #3 plug and new fuel filter just a couple of days ago. Same problem happened. Wires & all plugs (platinum) were replaced at 56,000 miles. Would it be brains of computer?? Ignition coil?? It doesn't seem to misfire when car is idling. Any specific help??

A. When you get a specific code that a certain cylinder is misfire, it's usually pretty accurate. Unfortunately it doesn't tell you why it's misfiring, just that it is.

Since you covered the electrical end of the problem, the next thing to look at is the fuel. it Since you only get a code on number three, we can assume fuel pressure and all that is okay. That leaves the PCM, the fuel injector itself or the wiring between the two.

P0300 is the Random/Multiple Cylinder Misfire Detected and if that is the one you're getting you'll have to look at the whole fuel and ignition system. If you are getting a P0303 which is Cylinder 3 Misfire Detected then you have to look at the specific cylinder. Also, after 30,000 miles it is not out of the realm of possibility the wires are bad.

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