Dodge RAM TRUCK 1500 1995 Service Manual page 390

BH
IGNITION SYSTEMS 8D - 1 7
POWERTRAIN CONTROL
MODULE (PCM) J9414-11
Fig. 24 PCM Location—Typical
fer to the Component Removal/Installation section of
this group.
For diagnostics, refer to the appropriate Powertrain
Diagnostic Procedures service manual for operation
of the DRB scan tool.
SPAFtI PLUGS
For spark plug removal, cleaning, gap adjustment
and installation, refer to the Component Removal/In­
stallation section of this group.
On 3.9L V-6 or 5.2/5.9L V-8 engines, spark plug ca­
ble boot heat shields are pressed into the cylinder
head to surround each cable boot and spark plug
(Fig. 25). 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. 25).
Fig. 25 Heat Shields—3.9L V-6 or 5.2J5.9L V-8
Engines
Faulty carbon and/or gas fouled plugs generally
cause hard starting, but they will clean up at higher
engine speeds. Faulty plugs can be identified in a
number of ways: poor fuel economy, power loss, de­
crease in engine speed, hard starting and, in general,
poor engine performance.
Remove the spark plugs and examine them for
burned electrodes and fouled, cracked or broken por­
celain insulators. Keep plugs arranged in the order
in which they were removed from the engine. An iso­
lated plug displaying an abnormal condition indicates
that a problem exists in the corresponding cylinder.
Replace spark plugs at the intervals recommended in
the maintenance chart in Group 0, Lubrication and
Maintenance.
Spark plugs that have low mileage may be cleaned
and reused if not otherwise defective. Refer to the
following Spark Plug Condition section of this group.
commoN
10B1AL OPERATING
The few deposits present on the spark plug will
probably be light tan or slightly gray in color. This is
evident with most' grades of commercial gasoline
(Fig. 26). There will not be evidence of electrode
burning. Gap growth will not average more than ap­
proximately 0.025 mm (.001 in) per 1600 km (1000
miles) of operation. Spark plugs that have normal
wear can usually be cleaned, have the electrodes
filed, have the gap set and then be installed.
NORMAL DRY BLACK COLD (CARBON) FOULING
\ DEPOSITS V \
J908D-15
Fig. 26 Normal Operation and Cold (Carbon) Fouling
Some fuel refiners in several areas of the United
States have introduced a manganese 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 can be
misdiagnosed as being caused by coolant in the com­
bustion chamber. Spark plug performance is not af­
fected by MMT deposits.