Spark Plug Condition-Cold Fouling/Carbon Fouling; Spark Plug Condition - Spark Plug Overheating - Jeep 1987 Wrangler Workshop Manual

ENGINES
ENGINE TUNE-UP PROCEDURES
Spark Plug Condition-Cold Fouling/Carbon Fouling
The deposits that c a u s e cold fouling are
basically carbon. LOW MILEAGE
P L U G S IN T H I S C O N D I T I O N M A Y B E
C L E A N E D .
60770E
A dry, black appearance of one or two plugs in a
set may be caused by sticking valves or faulty
spark plug wires.
Cold (carbon) fouling of the entire set may be
caused by a clogged air cleaner or a faulty
carburetor choke.
Spark
Plug Condition
- Spark
Plug Oterheating
Overheating is indicated by a white or gray
electrode insulator that also appears blistered.
P L U G S IN THIS CONDITION
MUST B E R E P L A C E D .
60770F
T h e i n c r e a s e in e l e c t r o d e gap will be
considerably in excess of 0.025mm per 1 609
km (0.001 in. per 1000 mi) of engine operation.
This suggests that a spark plug with a cooler
heat range rating should be used.
Overadvanced ignition timing, detonation and
cooling system malfunctions can also cause
spark plug overheating.
NOTE: Fuel refiners in several parts of the
United States have introduced a manganese
compound additive (MMT) for unleaded fuel.
During combustion, fuel with MMT causes the
entire tip of the spark plug to be coated with a
rust-colored deposit. This rust color may be
misdiagnosed as being caused by coolant in the
combustion chamber. Spark plug performance
is not affected by MMT deposits.
B-! >25