Misfire - Engine Miss

Step 6 - Once the misfiring cylinder has been located, remove the spark plug for inspection, before removing the spark plugs, mark the plug wires (if equipped) to identify their positions in the firing order, this will help for proper reassembly.

Remove Spark Plug

Step 7 - When a cylinder(s) runs rich it will carbon foul the spark plug causing it to short circuit. Malfunctions for this condition include partially plugged fuel injector or catalytic converter, low compression, failed fuel pressure regulator and excessive fuel mixture.

Carbon Fouled Spark Plug

Step 8 - A wet spark plug with gas or oil can mean a fuel injector is stuck open, fuel regulator has failed, no cylinder compression, broken piston oil control ring, blown head gasket or excessive leakage from the valve stem seals.

Spark Plug Fouled with Gas or Oil

Step 9 - A spark plug must be properly gapped with a specific measurement from the electrode, a misadjusted air gap can result in a misfire.

Misadjusted Air Gap

Step 10 - Using a proper spark plug with a correct air gap will help ensure operation of the ignition system.

Correct Spark Plug


Written by
Co-Founder and CEO of
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2015-01-09)