Posted: Fri May 22, 2009 6:09 pm Post subject: Missfires
2007 Chevrolet Impala SS.
one of the parameters I have my gauge set to in cyclic scan is misfires. I've noticed recently that I will get 1 or 2 misfires during normal light acceleration, or up to 8 when I'm backing up into a parking spot.
I then left the gauge on the misfires menu, where it shows which cylinders are misfiring. each of the cylinders will misfire at any given time.
however, I don't get any DTCs, CELs, or trouble codes or error messages of any kind. and also, the misfires will disappear from the misfire list, or go back down to zero in scan mode, in just a matter of 10 seconds or so after it says that there was a misfire. what could be going on?
Misfires are normal, especially when the engine is cold. It's only an issue when the number for a given cylinder gets above a factory determined limit indicating that something abormal is happening. This could be 50 per 200 engine revolutions for example.
The misfire counter resets after a predetermined period of time. I don't recall off of the top of me head what GM has set this value for your car, but it will will count misfires for a certain length of time then reset back to zero and start again.
I found this in the aeroforce forum, anyone care to comment on this?
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I've seen the aeroforce count misfires on my 3400. Mostly when it's not warmed up yet and I rev the engine a little. The misfires usually happen when I let off the gas. There may be like 2 or three or something, nothing that you would actually notice without the aeroforce telling you that you had misfires.
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that was actually me asking that question. I tried doing some research regarding if a misfire here and there is normal, I couldn't really find any conclusive answer.
After I installed my new plugs and wires I decided to check the misfires on my Interceptor (I had never done it before, so I don't have a baseline to compare to). As the statement in the OP said, it will occasionally read 2 to 4 misfires on random cylinders, but never when under heavy acceleration. Is this anything to be concerned about or am I being paranoid?
Protip: If you don't know what you're doing, don't do it.
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