what determines a missfire
or maby valve. huh 
TECH Enthusiast
Joined: Aug 2006
Posts: 542
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From: Memphis, TN
Causes: numerous things, ignition, improper fuel mixture, bad plug, bad fuel, yadda yadda
How PCM detects it: Slightly complicated, but basically it has to do with the engine being where the PCM expects it to be after ignition of the fuel. If it is behind where it should have been, then there was a misfire due to pumping losses etc. We are talking about degrees here, it is fairly sensitive. Depending on what cylinder(s) should have fired, determines which cylinder has the misfire code thrown. Pretty clever actually.
How PCM detects it: Slightly complicated, but basically it has to do with the engine being where the PCM expects it to be after ignition of the fuel. If it is behind where it should have been, then there was a misfire due to pumping losses etc. We are talking about degrees here, it is fairly sensitive. Depending on what cylinder(s) should have fired, determines which cylinder has the misfire code thrown. Pretty clever actually.
