Chrysler Stratus RHD 1997 Interactive Electronic Service Manual page 358

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DIAGNOSIS AND TESTING (Continued)
Some fuel refiners in several areas of the United
States have introduced a manganese additive (MMT)
for unleaded fuel. During combustion, fuel with MMT
may coat the entire tip of the spark plug with a rust
colored deposit. The rust color deposits can be misdi-
agnosed as being caused by coolant in the combustion
chamber. Spark plug performance is not affected by
MMT deposits.
COLD FOULING (CARBON FOULING)
Cold fouling is sometimes referred to as carbon
fouling because the deposits that cause cold fouling
are basically carbon (Fig. 27). A dry, black deposit on
one or two plugs in a set may be caused by sticking
valves or misfire conditions. Cold (carbon) fouling of
the entire set may be caused by a clogged air cleaner.
Cold fouling is normal after short operating peri-
ods. The spark plugs do not reach a high enough
operating temperature during short operating peri-
ods. Replace carbon fouled plugs with new
spark plugs.
FUEL FOULING
A spark plug that is coated with excessive wet fuel
is called fuel fouled. This condition is normally
observed during hard start periods. Clean fuel
fouled spark plugs with compressed air and
reinstall them in the engine.
OIL FOULING
A spark plug that is coated with excessive wet oil
is oil fouled. In older engines, wet fouling can be
caused by worn rings or excessive cylinder wear.
Break-in fouling of new engines may occur before
normal oil control is achieved. Replace oil fouled
spark plugs with new ones.
OIL OR ASH ENCRUSTED
If one or more plugs are oil or ash encrusted, eval-
uate the engine for the cause of oil entering the com-
bustion chambers (Fig. 28). Sometimes fuel additives
can cause ash encrustation on an entire set of spark
plugs. Ash encrusted spark plugs can be cleaned
and reused.
HIGH SPEED MISS
When replacing spark plugs because of a high
speed miss condition; wide open throttle opera-
tion should be avoided for approximately 80 km
(50 miles) after installation of new plugs. This
will allow deposit shifting in the combustion chamber
to take place gradually and avoid plug destroying
splash fouling shortly after the plug change.
ELECTRODE GAP BRIDGING
Loose deposits in the combustion chamber can
cause electrode gap bridging. The deposits accumu-
GROUND ELECTRODE
Fig. 28 Oil or Ash Encrusted
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. 29). This short circuits the electrodes. Spark
plugs with electrode gap bridging can be
cleaned and reused.
Fig. 29 Electrode Gap Bridging
SCAVENGER DEPOSITS
Fuel scavenger deposits may be either white or yel-
low (Fig. 30). 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
CENTER
IGNITION SYSTEM
ELECTRODE DEPOSITS
8D - 15