Inspect the spark plug for the following:
Deposit build-up that is closing the gap between the electrodes. Deposits are caused by oil or carbon fouling. Clean the spark plug..
Check for wet, black deposits on the insulator shell bore electrodes, 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.
Look for black, dry, fluffy carbon deposits on the insulator tips, exposed shell surfaces and electrodes, caused by a spark plug with an incorrect heat range, dirty air cleaner, too rich a fuel mixture or excessive idling. Install new spark plugs.
Light tan or gray deposits on the firing tip.
Pre-ignition. This identified by melted electrodes and a possibly damaged insulator. Metallic deposits on the insulator indicate engine damage. This may be caused by incorrect ignition timing, wrong type of fuel or the unauthorized installation of a heli-coil insert in place of the spark plug threads. Install a new spark plug.
Overheating. This is identified by a white or light gray spots and 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.
Fused deposits. These are identified by melted or spotty deposits resembling bubbles or blisters. These are caused by sudden acceleration. Install a new spark plug.
Removal & Installation
Fig. Removing ignition coils and spark plugs
Before servicing the vehicle, refer to the Precautions Section.
Remove or disconnect the following:
Negative battery cable
Engine room cover using power tool
To install, reverse removal procedure.