I have a 2006 Chevy Cobalt 2.2L and I got a reading of P0303 which is Cylinder 3 misfire. Why could possibly be the problem?
I have replaced spark plugs, ignition coil
pack, and checked compression and fuel
injector. All are okay. What else can I
possibly test to find out what the problem
Good luck with this. A guy from work fought for over a year with his '07 Cobalt having the same issue. This included 3 trips to the Chevy Dealer. Everything that you mentioned was done to his car as well. The only thing that helped was a Motovac cleaning of the fuel injection system. That cured it for about 6 months. When his check engine light came back on and we got the same trouble code (P0303) he got rid of the car! You can check with your local Chevy Dealer and see if any service bulletins have been issued on this. Perhaps a reflash of the PCM might fix it. I often wondered if an engine vibration was being picked up so the computer thinks it's misfiring. HTH. -Jim
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