Dodge RAM TRUCK 1500 1995 Service Manual page 391

8D -18 IGNITION SYSTEMS
B R
COLD F0ULING/CARB01 FOULING
Cold fouling is sometimes referred to as carbon
fouling. The deposits that cause cold fouling are ba­
sically carbon (Fig. 26). A dry, black deposit on one or
two plugs in a set may be caused by sticking valves
or defective spark plug cables. Cold (carbon) fouling
of the entire set of spark plugs may be caused by a
clogged air cleaner element or repeated short operat­
ing times (short trips).
WET FOULING OR G1S FOULING
A spark plug coated with excessive wet fuel or oil is
wet fouled. In older engines, worn piston rings, leak­
ing valve guide seals or excessive cylinder wear can
cause wet fouling. In new or recently overhauled en­
gines, wet fouling may occur before break-in (normal
oil control) is achieved. This condition can usually be
resolved by cleaning and reinstalling the fouled
plugs.
OIL O i ASH ENCRUSTED
If one or more spark plugs are oil or oil ash en­
crusted (Fig. 27), evaluate engine condition for the
cause of oil entry into that particular combustion
chamber.
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PR1673
Fig. 27 Oil or Ash Encrusted
ELECTRODE GAP BRIDGING
Electrode gap bridging may be traced to loose de­
posits in the combustion chamber. These deposits ac­
cumulate on the spark plugs during continuous stop-
and-go driving. When the engine is suddenly
subjected to a high torque load, deposits partially liq­
uefy and bridge the gap between electrodes (Fig. 28).
This short circuits the electrodes. Spark plugs with
electrode gap bridging can be cleaned using standard
procedures.
GROUND
J908D-11
Fig. 28 Electrode Gap Bridging
SCAfENGER DEPOSITS
Fuel scavenger deposits may be either white or yel­
low (Fig. 29). 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.
GROUND
ELECTRODE
COVERED
J908D-12
Fig. 29 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 can also separate the insulator
from the center electrode (Fig. 30). Spark plugs with
this condition must be replaced.