Spark Plug Condition - Jeep 1979 CJ-5 Technical & Service Manual

GENERAL SERVICE AND DIAGNOSIS 1A-15
A—Gap Bridging
Gap bridging may be traced to flying deposits in the
combustion chamber. Fluffy deposits may accumulate
on the plugs during in-town driving. When the engine is
suddenly put under heavy load, this material can melt
and bridge the gap.
B—Scavenger Deposits
Fuel scavenger deposits shown may be white or yel-
low. They may appear to be harmful but this is a normal
appearance caused by additives in certain fuel brands.
Such additives are designed to change the chemical n a -
ture of deposits to lessen misfire tendencies. Notice that
accumulation on the ground electrode and shell areas
may be heavy, but the material is easily removed. Such
plugs can be considered normal in condition and can be
cleaned using standard procedures.
C—Chipped Insulator
Chipped insulators usually result from bending the
center electrode while gapping of the plug. Under cer-
tain conditions, severe detonation can also split in-
sulator firing ends.
D—Pre-ignition Damage
Pre-ignition damage is caused by excessive temper-
atures. First the center electrode melts and, somewhat
later, the ground electrode. Insulators appear relatively
clean of deposits. Check for correct plug heat range,
overadvanced ignition timing and similar reasons for
overheating.
• LOW M I L E A G E PLUGS W I T H THIS C O N D I T I O N M A Y BE C L E A N E D
* * PLUGS W I T H T H I S C O N D I T I O N MUST BE REPLACED
6 0 7 7 0
Fig. 1A-3 Spark Plug Conditions
Fig. 1 A-2
Spark Plug Gap Check
Spark Plug Condition
Refer to figure 1A-3. Compare spark plugs with the
illustrations and the following descriptions.