Chrysler RAM TRUCK 2500 1994 Service Manual page 379

SB - 22 IGNITION SYSTEMS •
GROUND
ELECTRODE
STARTING
TO DISSOLVE
CENTER
ELECTRODE
DISSOLVED
J908D-14
Fig. 36 Preignition Damage
timing, detonation and cooling system malfunctions
can also cause spark plug overheating.
BLISTERED
WHITE OR
GRAY
COLORED
INSULATOR
J908D-16
Fig. 37 Spark Plug Overheating
SPARK PLUG SECONDARY CA1LES
On 3.9L V-6 or 5.2/5.9L V-8 engines, spark plug
heat shields are pressed into the cylinder head to
surround each spark plug cable boot and spark plug
(Fig. 38). These shields protect the spark plug boots
from damage (due to engine heat generated by the
exhaust manifolds) and should not be removed. After
the spark plug cable has been installed, the lip of the
cable boot should have a small air gap to the top of
the heat shield (Fig. 38).
T E S T I N G
Spark plug cables are sometimes referred to as sec­
ondary ignition cables or secondary wires. The cables
transfer electrical current from the distributor to in­
dividual spark plugs at each cylinder. The spark plug
cables are of nonmetallic construction and have a
built i n resistance. The cables provide suppression of
radio frequency emissions from the ignition system.
J9314-94
Fig. 38 Heat Shields—3.9L ¥-6 or 5.2/5.9L ¥-8
Engines
Check the high-tension cable connections for good
contact at the ignition coil, distributor cap towers
and spark plugs. Terminals should be fully seated.
The terminals and spark plug covers should be i n
good condition. Terminals should fit tightly to the ig­
nition coil, distributor cap and spark plugs. The
spark plug cover (boot) of the cable should fit tight
around the spark plug insulator. Loose cable connec­
tions can cause corrosion and increase resistance, re­
sulting i n shorter cable service life.
Clean the high tension cables with a cloth moist­
ened with a nonflammable solvent and wipe dry.
Check for brittle or cracked insulation.
When testing secondary cables for damage with an
oscilloscope, follow the instructions of the equipment
manufacturer. Note that 8.0L V-10 engines equipped
with distributor-less ignition (DIS) will display oppo­
site polarity spikes for paired cylinders.
I f an oscilloscope is not available, spark plug cables
may be tested as follows:
CAUTION: Do not leave any one spark plug cable
disconnected for longer than necessary during test­
ing. This may c a u s e possible heat damage to the
catalytic converter. Total test time must not exceed
ten minutes.
With the engine running, remove spark plug cable
from spark plug (one at a time) and hold next to a
good engine ground. I f the cable and spark plug are
in good condition, the engine rpm should drop and
the engine will run poorly. I f engine rpm does not
drop, the cable and/or spark plug may not be operat­
ing properly and should be replaced. Also check en­
gine cylinder compression.
With the engine not running, connect one end of a
test probe to a good ground. Start the engine and run
the other end of the test probe along the entire
length of all spark plug cables. I f cables are cracked