Chrysler Stratus RHD 1999 Electronic Service Manual page 283

8D - 12 IGNITION SYSTEM
DIAGNOSIS AND TESTING (Continued)
ELECTRODE GAP BRIDGING
Loose deposits in the combustion chamber can
cause electrode gap bridging. The deposits accumu-
late on the spark plugs during continuous stop-
and-go driving. When the engine is suddenly
subjected to a high torque load, the deposits partially
liquefy and bridge the gap between the electrodes
(Fig. 25). This short circuits the electrodes. Spark
plugs with electrode gap bridging can be
cleaned and reused.
Fig. 25 Electrode Gap Bridging
SCAVENGER DEPOSITS
Fuel scavenger deposits may be either white or yel-
low (Fig. 26). 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 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 consid-
ered normal in condition, cleaned and reused.
Fig. 26 Scavenger Deposits
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 also can separate the insulator
from the center electrode (Fig. 27). Spark plugs
with chipped electrode insulators must be
replaced.
Fig. 27 Chipped Electrode Insulator
PREIGNITION DAMAGE
Excessive combustion chamber temperature can
cause preignition damage. First, the center electrode
dissolves and the ground electrode dissolves some-
what later (Fig. 28). Insulators appear relatively
deposit free. Determine if the spark plugs are the
correct type, as specified on the VECI label, or if
other operating conditions are causing engine over-
heating.
Fig. 28 Preignition Damage
SPARK PLUG OVERHEATING
Overheating is indicated by a white or gray center
electrode insulator that also appears blistered (Fig.
29). The increase in electrode gap will be consider-
ably in excess of 0.001 in per 1000 miles of operation.
JA