Reading an Engines Spark Plugs

Looking at spark plug firing tips can tell you if your engine has a problem that needs correcting. They reflect the performance of a well tuned engine or a poorly maintained one. Bad spark plugs can cause overheating, rough running, power loss and even engine failure. Check your spark plugs regularly and use this chart as a guide to spot performance problems.

1. Normal
2. Normal with Red Coating Cause: Red coating resulting from fuel additive in unleaded fuel.
3. Fuel Fouled Cause: Faulty choke-overly rich fuel mixture ignition problems or plug heat range too cold.
4. Detonation Cause: Over-advanced timing, low octane fuel.
5. Worn Plug Cause: Plug is used beyond its service life. Need to replace.
6. Carbon Fouled Cause: Plug heat range too cold-extended low speed driving.
7. Pre-Ignition Cause: Plug heat range too hot-over advanced timing, air/fuel mixture too lean.
8. Oil Ash Fouled Cause: Poor oil control-worn rings, worn valve guides and valve seals.
9. Mechanical Damage Cause: Bent or damaged valve, broken or loose rod/pistion/wrist pin

Courtesy of Splitfire Spark Plugs

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