Explorer 4WD V6-4.0L VIN E (1999)
6. Inspect for carbon fouling, identified by black, dry, fluffy carbon deposits on 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.
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Clean the spark plug.
7. Inspect for normal burning.
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Check for light tan or gray deposits on the firing tip.
8. Inspect for pre-ignition, identified by melted electrodes and a possibly damaged insulator. Metallic deposits on the insulator indicate engine
damage, which 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.
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Install a new spark plug.
9. Inspect for over-heating, identified by a white or light gray insulator with small black or gray-brown spots and with bluish-burnt appearance of
electrodes. This can be caused by engine overheating, the wrong type of fuel, loose spark plugs, spark plugs with an incorrect heat range, low fuel
pump pressure or incorrect ignition timing.
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Install a new spark plug.
