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BASIC SPARK PLUG TROUBLE SHOOTING CHARTS CONDITION & POSSIBLE CAUSE CORRECTION Normal Spark Plug Condition Light Tan or Gray deposits No Action Electrode not burned or fouled No Action Gap tolerance not changed No Action Cold Fouling or Carbon Deposits Overrich air/fuel mixture Adjust air/fuel mixture, see ENGINE PERFORMANCE section Faulty choke Replace choke assembly, see ENGINE PERFORMANCE section Clogged air filter Clean and/or replace air filter Incorrect idle speed or dirty carburetor Reset idle speed and/ or clean carburetor Faulty ignition wires Replace ignition wiring Prolonged operation at idle Shut engine off during long idle Sticking valves or worn valve guide Check valve train Wet Fouling or Oil Deposits Worn rings and pistons Install new rings and pistons Excessive cylinder wear Rebore or replace block Excessive valve guide clearance Worn or loose bearing Gap Bridged Deposits in combustion chamber Clean combustion chamber of deposits Blistered Electrode Engine overheating Check cooling system Wrong type of fuel Replace with correct fuel Loose spark plugs Retighten spark plugs Over-advanced ignition timing Reset ignition timing see ENGINE PERFORMANCE Pre-Ignition or Melted Electrodes Incorrect type of fuel Replace with correct fuel Incorrect ignition timing Reset ignition timing see ENGINE PERFORMANCE Burned valves Replace valves Engine Overheating Check cooling system Wrong type of spark plug, too hot Replace with correct spark plug, see ENGINE PERFORMANCE Chipped Insulators Severe detonation Check for over-advanced timing or
1998 Chevrolet Pickup C1500 GENERAL INFORMATION Trouble Shooting - Basic Procedures
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