Chrysler 1998 Viper RT/10 Owner's Manual page 294

8D - 8 IGNITION SYSTEM
S R
DIAGNOSIS AND TESTING (Continued)
COLD FOULING (CARBON FOULING)
Cold fouling is sometimes referred to as carbon
fouling because the deposits t h a t cause cold fouling
are basically carbon (Fig. 16). A dry, black deposit on
one or two plugs i n 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 n o r m a l after short operating peri-
ods. The spark plugs do not reach a h i g h enough
operating temperature d u r i n g short operating peri-
ods. R e p l a c e c a r b o n fouled p l u g s w i t h n e w
s p a r k p l u g s .
FUEL FOULING
A spark plug t h a t is coated w i t h excessive wet fuel
is called fuel fouled. This condition is n o r m a l l y
observed d u r i n g h a r d start periods.Clean f u e l
f o u l e d s p a r k p l u g s w i t h c o m p r e s s e d a i r a n d
r e i n s t a l l t h e m i n t h e e n g i n e .
OIL FOULING
A spark plug t h a t is coated w i t h excessive wet o i l
is oil fouled. I n older engines, wet fouling can be
caused by w o r n rings or excessive cylinder wear.
Break-in fouling of new engines may occur before
normal o i l control is achieved. R e p l a c e o i l f o u l e d
s p a r k p l u g s w i t h n e w ones.
OIL OR ASH ENCRUSTED
I f one or more plugs are o i l or ash encrusted, eval-
uate the engine for the cause of oil entering the com-
bustion chambers (Fig. 17). Sometimes fuel additives
can cause ash encrustation on an entire set of spark
plugs. A s h e n c r u s t e d s p a r k p l u g s c a n b e c l e a n e d
a n d r e u s e d .
HIGH SPEED MISS
When replacing spark plugs because of a h i g h
speed miss condition;wide o p e n t h r o t t l e o p e r a t i o n
s h o u l d b e a v o i d e d f o r a p p r o x i m a t e l y 8 0 k m ( 5 0
m i l e s ) a f t e r i n s t a l l a t i o n o f n e w p l u g s . This w i l l
allow deposit shifting i n the combustion chamber to
take place gradually and avoid p l u g destroying
splash fouling shortly after the plug change.
E L E C T R O D E G A P B R f P G f f f G
Loose deposits i n the combustion chamber can
cause electrode gap bridging. The deposits accumu-
late on the spark plugs d u r i n g continuous stop-
and-go driving. W h e n the engine is suddenly
subjected to a h i g h torque load, the deposits partially
liquefy and bridge the gap between the electrodes
(Fig. 18). This short circuits the electrodes. S p a r k
p l u g s w i t h e l e c t r o d e g a p b r i d g i n g c a n b e
c l e a n e d a n d r e u s e d .
J908D-11
Fig. 18 Electrode Gap Bridging
SCAVENGER DEPOSITS
Fuel scavenger deposits may be either w h i t e or yel-
low (Fig. 19). They may appear to be harmful, but
are a normal condition caused by chemical additives
i n certain fuels. These additives are designed to
change the chemical nature of deposits and decrease
spark plug misfire tendencies. Notice t h a t accumula-
t i o n on the ground electrode and shell area may be
heavy but the deposits are easily removed. S p a r k
p l u g s w i t h s c a v e n g e r d e p o s i t s c a n b e c o n s i d -
e r e d n o r m a l i n c o n d i t i o n , c l e a n e d a n d r e u s e d .