Grand Cherokee 2WD L6-4.0L VIN S (1997)
Preignition Damage
Preignition damage is usually caused by excessive combustion chamber temperature. The center electrode dissolves first and the ground electrode
dissolves somewhat latter. Insulators appear relatively deposit free. Determine if the spark plug has the correct heat range rating for the engine.
Determine if ignition timing is over advanced, or if other operating conditions are causing engine overheating. (The heat range rating refers to the
operating temperature of a particular type spark plug. Spark plugs are designed to operate within specific temperature ranges. This depends upon the
thickness and length of the center electrodes porcelain insulator.)
Red, Brown, Yellow or White Deposits - Fuel Additives
SCAVENGER DEPOSITS
Scavenger Deposits
Fuel scavenger deposits may be either white or yellow. They may appear to be harmful, but are a normal condition caused by chemical additives in
certain fuels. These additives are designed to change the chemical nature of deposits and decrease spark plug misfire tendencies. Notice that
accumulation on the ground electrode and shell area may be heavy but the deposits are easily removed using standard procedures. Spark plugs
with scavenger deposits can be considered normal in condition, cleaned and reused.
Scavenger Deposits
Scavenger Deposits
Fuel scavenger deposits may be either white or yellow. They may appear to be harmful, but this is a normal condition caused by chemical additives in
