Why is there burn marks on the outside ceramic on a spark plug on a 1998 F150?

Answer 1

Your spark plugs/wires may be bad or the ceramics may be cracked. Either of these cases would cause a bad connections with the spark plug wires and might cause "jumping" which would cause burn marks along the outside of the spark plug. If your spark plugs appear fine, check the wires for cracks, burn marks, or weardown. Also, and easy way to tell if you DO have a jump somewhere in your spark plugs is to run your car in a dark area and watch for sparks. It should look like a flashlight turning on or off very rapidly. It that doesn't work, (this way is a little more...painful.) Touch the top of your distributor cap lightly, then with more and more pressure, leaving your hand down for longer periods of time until your palm is flush with the cap. If at anytime you feel a jolt or shock, then there is definitely a jump somewhere in your spark/engine array. Doing a minor tuneup may also fix this.

If there are burns on your spark plugs, replace them right away and see if the problem persists. (replacing the dist. cap and wires is also a wise decision, and should cost you less than 100 bucks.)

AnswerThere are no wires or distributer cap for a 1998 F150 Triton engines

Answer 2

Causes can include the engine overheating, incorrect spark plug heat range, a loose spark

plug, incorrect ignition timing or too lean of an air/fuel mixture.