Spark Plug Test

WARNING: This page is about a different car, the 2008 Mitsubishi Outlander. However, it is still accessible from the selected car via links, so may be relevant.

Remove the spark plug and connect to the ignition coil.

Fig 1: Identifying Spark Plug
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
Ground the spark plug outer electrode (body), and crank the engine.
Check that there is an electrical discharge between the electrodes at this time.

Fig 2: Identifying Defective Insulation Of Spark Plug
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.