I took my grand prix into autozone and found out I have error code: P0303 - Cylinder #3 misfire.

I just replaced all six spark plugs and all the spark plug wires, and no difference. The code still appears.

The next step I'm going to take is replacing the coil packs. Is there a way to test which coil is bad ? Do I need to replace all three coils?

Any help would be appreciated.

Thanks,
-Nick-

If you're having trouble with #3, replace the coil pack responsible for #3.

There are three things required for a proper combustion cycle. Fuel, air, and spark. Air is pretty much taken care of by the valve opening. Fuel, if you're injector is sticking or something then you're probably going to get a very weird running engine. Spark, you're already on the right rack with that.

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You can test the resistance across the coil packs with on ohm meter. Place the leads across the 2 pegs that the plug wires connect to on the pack and compare the readings between the 3 packs, they should all be fairly close. But like sabrewings said if it says cyl#3 then that's most likly the bad pack. When you change it it's not a bad idea to take the whole ignition module off and clean off the corrosion that will most likly be behind it.

Thank you very much for the help.

Did you get your problem figured out?

I was of the understanding, with the type of coils on this engine, typically both sides of the coil go bad at the same time. Therefore 2 cylinders would misfire. Is this not correct?

^^It can be, but sometimes the coil shorts or carbon tracks and only one cylinder gets it, the free way to test a coil is to switch it with another of the coils and see if the missfire follows

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2002 GT...Wizardair, ZZP 2.5 o/r dp, Special Eddition two-tone leather interior added, HUD added, 12" Brake Upgrade, ZZP strut tower bars, gmpp sway bars,-6an braided SS fuel hoses , Hptuned, Top Swaped.....
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Problem solved and my car runs beautifully. It must have been either the spark plugs or the wires because I replaced them both and it runs like a champ now.

Excellent! Congrats!

I"m just a little confused as to what your last fix was. Did you change the coil(s)? Did you replace the plugs and wires a second time?

I'm having some trouble with my 99 GTP and I have already replaced all 3 coils, ignition module, plugs and wires. I'm getting a code for misfire in cylinder #1. The Pontiac dealer in my area is more concerned with selling me on anything else except for fixing my problem.

I replaced all of my spark plugs and bought new wires. That did the trick and everything is working great now.