Spark Plug And Ignition Coll Wires; Wire Resistance Test; Ignition Coil; Electrode Gap Bridging - Jeep J-10 Series 1982 Technical & Service Manual

A—Electrode Gap Bridging
Electrode gap bridging may be traced to loose deposits
in the combustion chamber. These deposits accumulate
on the 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
(i.e., short circuit the electrodes).
B—Scavenger Deposits
Fuel scavenger deposits may be either white or yel
low. They may appear to be harmful but this is a normal
condition caused by chemical additives in certain fuels.
Such additives are designed to change the chemical na
ture of deposits and decrease spark plug misfire tenden
cies. Notice that accumulation on the ground (side)
electrode and shell area may be heavy, but the deposits
are easily removed. Plugs with scavenger deposits can
be considered normal in condition and can be cleaned
using standard procedures.
C—Chipped Electrode Insulator
A chipped electrode insulator usually results from
bending the center electrode while adjusting the spark
plug electrode gap (separation). Under certain condi
tions, severe detonation can also separate the insulator
from the center electrode.
D—Preignition Damage
Preignition damage is caused by excessive combustion
chamber temperature. First, the center electrode dis
solves and, somewhat later, the ground (side) electrode.
Insulators appear relatively deposit free. Determine if
the spark plug has the correct heat range rating, if
ignition timing is overadvanced or if other conditions
are causing engine overheating.
NOTE: The heat range rating refers to the operating
temperature of a particular type spark plug. Spark
plugs are designed to operate within specific temper
ature ranges depending upon the thickness and length of
the center electrode porcelain insulator.
E—Cold Fouling (or Carbon Fouling)
The deposits that cause cold fouling are basically car
bon. A dry, black deposit on one or two plugs in a set
may be caused by "sticking" valves or defective spark
plug wires. Cold (carbon) fouling of the entire set may be
caused by a clogged air cleaner, a sticking exhaust mani
fold heat valve (eight-cylinder engine only) or a faulty
carburetor choke.
F—Spark Plug Overheating
Overheating is indicated by a white or gray electrode
insulator that also appears blistered. The increase in
electrode gap (separation) will be considerably in excess
of 0.001 inch per 1000 miles (0.025 mm per 1609 km) of
engine operation. This suggests that a 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: Some fuel refiners in several areas of the
United States have introduced a manganese additive
GENERAL SERVICE AND DIAGNOSIS 1A-17
(MMT)for unleaded fuel During combustion, fuel with
MMTcauses the entire tip of the spark plug to be coated
ivith a rust-cohred deposit. This rust color may be mis
diagnosed as being caused by coolant in the combustion
chamber. Spark plug performance is not affected by
MMT dejmsits.
Spark Plug and Ignition Coll Wires
To remove wires from spark plugs, twist the rubber
protector boot approximately 1/2-turn to break the seal.
Grasp the boot and pull it from the plug with constant
force. Do not pull on the wire itself because this will
damage the conductor and terminal connection.
To remove wires from the distributor cap or ignition
coil tower, loosen the boot first, then grasp the upper
part of the boot and the wire and gently pull straight up.
Win RwisUnct Tut
Do not puncture spark plug wires with a probe while
performing any test. This may cause a separation in the
conductor. The preferred method is to remove the sus
pected wire and use an ohmmeter to test for the correct
resistance according to the length of the particular wire.
Refer to Spark Plug and Coil Wire Resistance Wire
Values chart.
Spark Plug and Coil Wire Resistance Values
Inches
Ohira
0to15
15 to 25
25 to 35
Over 35
3.000 to 10,000
4.000 to 16.000
6.000 to 20.000
8.000 to 25,000
60748
When installing spark plug wires and the ignition coil
high voltage wire, ensure mechanically tight con
nections are made at the spark plugs, distributor cap
tower and ignition coil tower. The wire protector boots
on the spark plugs and distributor cap towers and coil
tower must fit tightly. A partially seated wire terminal
creates an air separation (resistance) in the high voltage
circuit and the resulting arcing will cause terminal cor
rosion, wire conductor damage and decrease the voltage
at the spark plugs.
When replacing spark plug wires, route the wires cor
rectly and secure them within the proper retainers. Fail
ure to route the wires properly can result in radio
ignition noise and cross ignition of the plugs, or short
circuit the wires to ground.
Ignition Coil
Always test a suspected defective ignition coil on the
engine. Because a coil may "break down" after the en
gine has heated it to operating temperature, it is impor
tant that the coil be at normal operating temperature