To determine if a spark plug is damaged, a comprehensive assessment can be conducted using methods such as visual inspection, resistance testing, spark test, and gap measurement. During visual inspection, the normal electrode should be light brown or grey. Black carbon deposits may indicate an overly rich air-fuel mixture or incomplete combustion, while white deposits may result from a lean mixture or engine overheating. Oil contamination or electrode erosion also necessitates replacement. Resistance testing requires a multimeter. Abnormal resistance values (too high or too low) will affect ignition performance. For the spark test, connect the spark plug to the ignition coil and ground it, then observe the spark between the electrodes. Gap measurement uses a feeler gauge. The standard gap is typically 0.6 to 1.3 millimeters; either too large or too small a gap impairs ignition effectiveness and should be adjusted according to the vehicle model. Regular spark plug inspection helps detect issues like abnormal combustion or insufficient ignition energy early, preventing engine misfires, increased fuel consumption, or difficulty starting. It is best to replace spark plugs every 20,000 to 30,000 kilometres or as specified in the maintenance manual to ensure efficient engine operation.
