Spark Plug: Service and Repair

REMOVAL
1. Remove the ignition coil. For additional information, refer to Ignition Coil.







2. Remove the spark plugs.

NOTE: Use compressed air to remove any foreign material from the spark plug well before removing the spark plugs.







3. Inspect for a bridged gap.
^ Check for deposit build-up closing the gap between electrodes. Deposits are caused by oil or carbon fouling.
^ Clean the spark plug.







4. Inspect for oil fouling, identified by wet, black deposits on the insulator shell bore electrodes. This is caused by excessive oil entering the combustion chamber through worn rings and pistons, excessive valve-to-guide clearance or worn or loose bearings.
^ Correct the oil leak concern.
^ Install a new spark plug.







5. Inspect for carbon fouling, identified by black, dry, fluffy carbon deposits on the insulator tips, exposed shell surfaces and electrodes. This is caused by a spark plug with an incorrect heat range, dirty air cleaner, too rich a fuel mixture or excessive idling.
^ Clean the spark plug.







6. Inspect for normal burning.
^ Check for light tan or gray deposits on the firing tip.







7. Inspect for pre-ignition, identified by melted electrodes and possibly a damaged insulator. Metallic deposits on the insulator indicate engine damage. Pre-ignition may be caused by incorrect ignition timing, wrong type of fuel or the installation of a heli-coil insert in place of the spark plug threads.
^ Install a new spark plug.







8. Inspect for overheating, identified by a white or light gray insulator with small black or gray-brown spots with bluish-burnt appearance of electrodes. This is caused by engine overheating, wrong type of fuel, loose spark plugs, spark plugs with an incorrect heat range, low fuel pump pressure or incorrect ignition timing.
^ Install a new spark plug.







9. Inspect for fused spot deposits, identified by melted or spotty deposits resembling bubbles or blisters. This is caused by sudden acceleration.
^ Clean the spark plug.







10. Adjust the spark plug gap as necessary.

INSTALLATION
1. To install, reverse the removal procedure.