SCAVENGER DEPOSITS
Fuel scavenger deposits may be either white or yel-
low (Fig. 16). They may appear to be harmful, but
this is a normal condition caused by chemical addi-
tives in certain fuels. These additives are designed to
change the chemical nature of deposits and decrease
spark plug misfire tendencies. Notice that accumula-
tion on the ground electrode and shell area may be
heavy, but the deposits are easily removed. Spark
plugs with scavenger deposits can be considered nor-
mal in condition and can be cleaned using standard
procedures.
CHIPPED ELECTRODE INSULATOR
A chipped electrode insulator usually results from
bending the center electrode while adjusting the
spark plug electrode gap. Under certain conditions,
severe detonation can also separate the insulator
from the center electrode (Fig. 17). Spark plugs with
this condition must be replaced.
PREIGNITION DAMAGE
Preignition damage is usually caused by excessive
combustion chamber temperature. The center elec-
trode dissolves first and the ground electrode dis-
solves somewhat latter (Fig. 18). 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
Fig. 14 Oil or Ash Encrusted
Fig. 15 Electrode Gap Bridging
1 – GROUND ELECTRODE
2 – DEPOSITS
3 – CENTER ELECTRODE
Fig. 16 Scavenger Deposits
1 – GROUND ELECTRODE COVERED WITH WHITE OR
YELLOW DEPOSITS
2 – CENTER ELECTRODE
Fig. 17 Chipped Electrode Insulator
1 – GROUND ELECTRODE
2 – CENTER ELECTRODE
3 – CHIPPED INSULATOR
DN IGNITION SYSTEM 8D - 9
DIAGNOSIS AND TESTING (Continued)
To Next Page
Loading...
