Spark Plug Test

Remove the spark plug and connect to the ignition coil.

Fig 1: Grounding Spark Plug To Engine
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: Inspecting Spark Plug For Electrical Discharge
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.