Tune up

Step 11 - Inspect coil electrical terminals for corrosion or signs of heat which indicates failure.

Coil Electrical Terminals

Step 12 - Once the coil has been removed, use a spark plug socket and extension to remove the spark plug. (Note: A spark plug socket is rubber lined as to not damage the plug.)

Spark Plug Socket

Step 13 - Using a socket wrench, turn the plug counterclockwise to remove it from the well.

Removing Spark Plug

Step 14 - After loosening the plug, carefully remove it to inspect. This inspection can give information on how that particular cylinder is running. If the plug is white, or slightly yellow with little flecks of gray or black the cylinder is running pretty well. If the plug is wet with fuel, the cylinder is not firing, this could be low compression or a faulty ignition coil. If the plug is covered in black soot, the mixture is extremely rich indicating a vacuum leak or a misfire on opposing cylinders.

Spark Plug Removed

Step 15 - Once removed, match the new replacement spark plug to the old plug. Its important to install the correct plug or the engines performance will be hindered. Also check the plug "gap" which should be consistent and to the manufacturer recommendations.

New 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 2013-11-28)