An article showing how to diagnose common spark plug conditions and their causes.
Examining a vehicle's spark plugs can help determine the current running conditions of the engine. Bad spark plugs can cause detonation, pre-ignition, rough idling, poor running conditions, power loss and even engine failure. Check the engine spark plugs each time a routine tune up is done.
| 1. Normal |  |
| 2. Normal with Red Coating Cause: A common result from fuel additive in unleaded fuel. |
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| 3. Fuel Fouled Cause: Signals a fuel rich mixture. Can also mean the wrong spark plug is being used |
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| 4. Detonation Cause: Over-advanced timing, low octane fuel. Excessive carbon build up |
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| 5. Worn Plug Cause: Plug is used beyond its service life and needs to replaced. |
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| 6. Carbon Fouled Cause: Fuel Rich mixture with extended low speed driving. |
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| 7. Pre-Ignition Cause: Spark timing is wrong Lean-fuel mixture could be present |
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| 8. Oil Ash Fouled Cause: Piston rings excessively worn Valve guide seals need to be replaced Cylinder heads may need full overhaul Engine may need complete overhaul |
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| 9. Mechanical Damage Cause: Wrong plug being used Excessive low end engine damage has occurred |
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Article Type:
Maintenance
Category:
Electrical Tech