On-Vehicle Service - Jeep J-10 Series 1982 Technical & Service Manual

1G-4 IGNITION SYSTEMS
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1 — R-INDICATES RESISTOR-TYPE PLUG.
2 — 4-INDICATES 14 mm THREADS.
3 —4-HEAT RANGE.
4 — T-TAPERED SEAT.
S-EXTENDED TIP
5 —X-SPECIALGAP.
90831
Rg. 16-7 Spark Plug Code
Refer to the Tune-Up Specifications listed in Chapter
1A for spark plug application and gap sizes. Always
replace plugs with the correct plug type listed in the
tune-up specifications.
Normal engine operation is usually a combination of
idling, slow-speed, and high-speed driving. Occasional
high-speed driving is needed for good spark plug per
formance because it provides increased combustion heat
that burns away deposits of carbon or oxide that have
built up from frequent idling or continual stop-and-go
driving.
The spark plugs are protected by insulating boots
made of special heat-resistant silicone rubber that cov
ers the spark plug terminal and extends downward over
a portion of the porcelain insulator. These boots prevent
arcing, which causes engine misfire. The dirt film that
builds up on the exposed portion of the plug will not
cause arcing.
NOTE: Do not mistake corona discharge for arcing or
as the result of a shorted insulator. Corona is a steady
blue light haze appearing around the insulator, just
above the shell crimp. It is the visible evidence ofa high
electrostatic voltage field and has no effect on ignition
performance. Usually it can be detected only in dark
ness. This discharge may repel dust particles and leave a
clear ring on the insulatorjust above the shell This ring
is sometimes mistakenly regarded as evidence that com
bustion gases have blown out between shell and
insulator.
Ignition Switch
The mechanical key-controlled ignition switch is lo
cated in the steering column on the right-hand side just
below the steering wheel. The electrical switching por
tion of the assembly is separate from the key and lock
cylinder and is located on top of the column. Both func
tion together through the action of the actuator rod.
For a complete explanation of the key and lock cylin
der, and the actuator rod, refer to Chapter 2H—Steering
Column. Refer to Chapter 3R—Lighting Systems for the
detailed explanation of the electrical components.
DIAGNOSIS
HEI Distributor and Ignition Coll
Refer to Ignition System Troubleshooting Chart
Spark Plugs
Faulty or dirty plugs may perform well at idling
speed, but at higher speeds they frequently fail. Faulty
plugs are identified in a number bf ways: poor fuel
economy, power loss, loss of speed, hard starting and, in
general, poor engine performance.
Spark plugs may also fail because of carbon fouling,
excessive gap, or a broken insulator.
Fouled plugs may be verified by inspecting for black
carbon deposits. The black deposits are usually the re
sult of slow-speed driving when sufficient engine oper
ating temperature is seldom reached. Worn pistons and
rings, faulty ignition, an over-rich air/fuel mixture and
the use of spark plugs with too low of a heat range will
also result in carbon deposits.
Excessive gap wear, on plugs with low mileage, in
dicates that the engine has been operating at high
speeds continuously or with loads that are greater than
normal, or that plugs that have too high of a heat range
are being used. Electrode wear may also be the result of
the plug being overheated. This can be caused by com
bustion gases leaking past the threads because of in
sufficient tightening of the spark plug. An excessively
lean air/fuel mixture will also result in abnormal elec
trode wear.
A broken lower insulator is usually the result of im
proper installation or carelessness when regapping the
plug. Broken upper insulators usually result from a poor
fitting wrench or an outside blow. A cracked insulator
may not be evident immediately, but will as soon as oil
or moisture penetrates the crack. The crack will usually
be located just below the crimped part of the shell and
may not be visible.
Broken lower insulators usually result from care
lessness when regapping and are generally visible. This
type of break may also result from the plug operating
too "hot," which may occur during periods of extended
high-speed operation or with heavy engine loads. When
regapping a spark plug, always make the gap adjust
ment by bending the ground (side) electrode. Spark
plugs with broken insulators should always be replaced.
Spark plugs should be tightened with 15 to 25 foot
pounds (20 to 34 N»m) torque.
ON-VEHICLE SERVICE
HEI Distributor and Ignition Coil
Precautions and General Information
(1) When performing cylinder compression tests,
disconnect ignition switch (BAT) wire at distributor.