Spark Plug: Testing and Inspection

INSPECTION
- Check the electrodes and insulators for cracks. Replace if faulty.
- Check the electrodes for wear and replace as necessary.
- Check the gaskets for damage and replace as necessary.
- Check insulation resistance with an ohmmeter. Replace if defective.
SPARK PLUG INSULATION RESISTANCE
50 M ohms

- Check spark plug gap. Adjust or replace as necessary.
SPARK PLUG ELECTRODE GAP
1.05 mm (0.040 in)

- If spark plug fouling is excessive, check fuel and electrical systems for possible causes. If those systems are normal, install spark plugs of a higher heat range.
- If burning of the electrodes or insulator is considerable, install spark plugs of a lower heat range.

SOOTY SPARK PLUGS
If the electrodes and insulators are fouled with carbon or oil, the engine will operate efficiently. There are a number of possible causes:
- Rich fuel mixture.
- Retarded ignition timeing.
- Excessive engine wear (oil in cylinders).
- Incorrect plug gap.

BLISTERED OR SCORCHED SPARK PLUGS
This condition is caused by excessive temperature at the spark plug. Common causes are:
- Lean fuel mixture.
- Advanced ignition timing.
- Incorrect plug gap.
- Incorrect plug heat range.