Spark Plug Test

Fig 1: Identifying Spark Plug

Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.

Remove the spark plug and connect to the ignition coil.

Fig 2: Identifying Spark Plug Defective Insulation Areas
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.