1993 DODGE TRUCK spark plugs

0 - 14
LUBRICATION
AND
MAINTENANCE

•
ENGINE
MAINTENANCE

INDEX

page
Air
Injection
Systems/Air Pump
. 17

Air-Conditioner
Compressor
21
Battery
19

Cooling System
15

Crankcase
Ventilation
System
17
Diesel Engine
Air Filter
Canister
17

Drive Belts
20
Engine
Air
Cleaner
Filter
Element
16

Engine Break-In
14

Engine
Oil 14

Engine
Oil
Change
and Filter
Replacement
15

Exhaust Gas
Recirculation
(EGR) System
...... 19
page
Exhaust
Manifold
Heat
Control
Valve
. 17
Exhaust System
, 21

Fuel System
18

Hoses
and
Fittings
16
Ignition
Cables,
Distributor
Cap and
Rotor
...... 19

Ignition
Timing
. 19

Oxygen
(02)
Sensor
19
Rubber/Plastic Components
20

Spark Plugs
. 19

Throttle
Control
Linkage
18

Vacuum Operated, Emission
Control
Components
19

ENGINE BREAK-IN
After first starting a new engine, allow it to idle
for 15 seconds before shifting into a drive gear. Also:
• Drive the vehicle at varying speeds less than 88
km/h (55 mph) for the first 480 km (300 miles).
• Avoid fast acceleration and sudden stops.
• Do not drive at full-throttle for extended periods of
time
• Do not drive at constant speeds
• Do not idle the engine excessively A special break-in engine oil is not required. The
original engine oil installed is a high quality lubri­
cant. New engines tend to consume more fuel and oil un­
til after the break-in period has ended.

ENGINE
OIL SPECIFICATIONS

API SERWICE
GRADE
Use an engine oil that conforms to API Service
Grade S5 SG/CD or SG/CE. MOPAR®provides engine
oils that conform to all of these service grades.

SULFATED ASH—DIESEL ENGINES
Oils that contain an excessive amount of sulfated
ash can cause deposits to develop on Diesel engine
valves. These deposits can result in valve wear.

SAE
WISC0SITY
An SAE viscosity grade is used to specify the vis­
cosity of engine oil. SAE 30 specifies a single viscos­
ity engine oil.
Engine oils also have multiple viscosities. 10W-30

<
5W-30

1
1 1

F
-20 0 10 20 32 60 80 100

C
-29 -18 -12 -7 0 16 27 38
ANTICIPATED
TEMPERATURE RANGE BEFORE
NEXT
OIL
CHANGE
J9000-39

Fig.
1 Temperature/Engine Oil Viscosity—Gasoline
Engines

-12°C
-18°C 10°F
0°F- 15W-40

-23°c(^-10eF

I
10W-30
WITH
WITHOUT
BLOCK HEATER
BLOCK
SYNTHETIC
OIL

HEATER
10W-30 5W-30

J9100-29

Fig.
2 Temperature/Engine Oil Viscosity—Diesel
Engines

ENERGY
G0NSERWING
OIL
An Energy Conserving type oil is recommended for
gasoline engines. They are designated as either EN­
ERGY CONSERVING or ENERGY CONSERVING

II.
OIL
LEVEL
INDICATOR (DIPSTICK)

GASOLINE ENGINES
The engine oil indicator is located at the right
front of the engine.

•

LUBRICATION
AND
MAINTENANCE
0 - 19 ETBE— This fuel is a mixture of unleaded gasoline
and up to 17 percent ETBE (Ethyl Tertiary Butyl

Ether).
Unleaded gasoline blended with ETBE is ac­ ceptable.
METHANOL—Do not use unleaded gasoline
blended with methanol. The use of this type of alco­ hol can result in engine performance and damage to
critical components. Engine problems that result
from the use of methanol possibly will not be covered by the new vehicle warranty.
Certain brands of unleaded gasoline contain a per­
centage of unidentified alcohol. These types of un­
leaded gasoline are not recommended.

ADDITIVES MIXED
WITH
GASOLINE
Use of fuel system cleaning additives should be
avoided. Many of these solutions could contain highly
active solvents. This type of solvent can be harmful
to the gasket and diaphragm material within the fuel system.

DIESEL
ENGINE FUEL REQUIREMENTS
All Diesel engines normally can use number 2D
Diesel fuel for most year-round operations. A fuel
conforming to ASTM Specification D-975 is recom­
mended. For extreme cold-weather operation (below
-18°C/0°F), or for prolonged cold-climate operation ei­
ther:
• Use No. ID fuel, or
• Add an equal quantity of kerosene to No. 2D fuel (a 50/50 mixture).
Both methods provide protection against fuel gel­
ling and waxing.
Diesel fuel seldom is without water contamination.
To help prevent fuel system malfunctions, drain all accumulated water from the separators periodically.

VACUUM OPERATED,
EMISSION
CONTROL
COMPONENTS

MAINTENANCE SCHEDULE
The following emission controls should be replaced
at the interval specified in the maintenance sched­

ule:

• Bi-level purge check valves
• Delay valves
• Heated air temperature sensor (HATS)
• Air cleaner vacuum motors

EXHAUST
GAS RECIRCULATION (EGR)
SYSTEM

MAINTENANCE SCHEDULE
Replace the EGR valve and tube, and clean the
passages at the interval specified in maintenance schedule. If necessary, refer to Group 25—Emission
Control Systems for additional information.
OXYGEN
(02)
SENSOR

MAINTENANCE SCHEDULE
Replace the 02 sensor at the interval specified in
maintenance schedule.

IGNITION
CABLES,
DISTRIBUTOR CAP AND

ROTOR

MAINTENANCE SCHEDULE
Replace the ignition cables, distributor cap, and ro­
tor at the interval specified in maintenance schedule.
Inspect the distributor for excessive wear and re­
place, as necessary. Refer to Group 8D—Ignition Sys­
tems for additional information.

IGNITION TIMING
MAINTENANCE SCHEDULE
Test and adjust, if necessary, the ignition timing at
the interval specified in maintenance schedule. Refer
to the specifications listed on the engine Emission Control Information label. Refer to Group 8D—Igni­
tion Systems and to Group 25—Emission Control Systems for additional service information.

SPARK
PLUGS MAINTENANCE SCHEDULE
Replace the spark plugs at the interval specified in
maintenance schedule. Refer to the Spark Plugs
chart below and to Group 8D—Ignition Systems for additional service information.

SPARK
PLUGS
ENGINE
SPARK

PLUG
SPARK

PLUG
GAP
TORQUE

3.9L
5.2L
5.9L
RN12YC

RN12YC

RN12YC
0.9 mm
(0.035
in.)
0.9 mm
(0.035
in.)
0.9 mm
(0.035
in.) 41 N*m (30 ft. lb.)
41 NVn (30 ft. lb.)
41 N*m (30 ft. lb.)

J9100-17

BATTERY

MAINTENANCE SCHEDULE
Replace battery at interval specified in mainte­
nance schedule.

7 - 30
COOLING
SYSTEM

•

COOLING
SYSTEM

Fig.
39
Pressure
Testing
Cooling
System—Typical bulges while testing, replace as necessary. Observe
gauge pointer and determine condition of cooling sys­
tem according to following criteria:
Holds Steady: If pointer remains steady for two
minutes, serious coolant leaks are not present in sys­
tem. However, there could be an internal leak that does not appear with normal system test pressure. If
it is certain that coolant is being lost and leaks can­
not be detected, inspect for interior leakage or per­
form Internal Leakage Test.
Drops Slowly: Indicates a small leak or seepage is
occurring. Examine all connections for seepage or
slight leakage with a flashlight. Inspect radiator,

hoses,
gasket edges and heater. Seal small leak holes
with a Sealer Lubricant (or equivalent). Repair leak
holes and inspect system again with pressure ap­
plied.
Drops Quickly: Indicates that serious leakage is
occurring. Examine system for external leakage. If
leaks are not visible, inspect for internal leakage.
Large radiator leak holes should be repaired by a
reputable radiator repair shop.
INTERNAL LEAKAGE INSPECTION Remove engine oil pan drain plug and drain a
small amount of engine oil. If coolant is present in
the pan, it will drain first because it is heavier than
oil.
An alternative method is to operate engine for a
short period to churn the oil. After this is done, re­
move engine dipstick and inspect for water globules.
Also inspect transmission dipstick for water globules and transmission fluid cooler for leakage.

WARNING:
WITH
PRESSURE TESTER TOOL
7700
INSTALLED
ON
RADIATOR,
DO
NOT ALLOW
PRES­

SURE
TO
EXCEED
110 KPA (20
PSI). PRESSURE

WILL
BUILD
UP
QUICKLY
IF A
COMBUSTION LEAK

IS
PRESENT.
TO
RELEASE
PRESSURE,
ROCK

TESTER
FROM SIDE
TO
SIDE. WHEN REMOVING

TESTER,
DO NOT
TURN TESTER MORE THAN
1/2

TURN
IF
SYSTEM
IS
UNDER
PRESSURE.
Operate engine without pressure cap on radiator
until thermostat opens. Attach a Pressure Tester to
filler neck. If pressure builds up quickly it indicates a combustion leak exists. This is usually the result of
a cylinder head gasket leak or crack in engine. Re­
pair as necessary.
If there is not an immediate pressure increase,
pump the Pressure Tester. Do this until indicated
pressure is within system range of 110 kPa (16 psi). Fluctuation of gauge pointer indicates compression or
combustion leakage into cooling system.
Because the vehicle is equipped with a catalytic
converter, do not remove spark plug cables or short
out cylinders (non-diesel engines) to isolate compres­
sion leak.
If the needle on dial of pressure tester does not
fluctuate, race engine a few times to check for an ab­ normal amount of coolant or steam. This would be
emitting from exhaust pipe. Coolant or steam from
exhaust pipe may indicate a faulty cylinder head
gasket, cracked engine cylinder block or cylinder
head. A convenient check for exhaust gas leakage into
cooling system is provided by a commercially avail­ able Block Leak Check tool. Follow manufacturers
instructions when using this product.
COMBUSTION LEAKAGE TEST-WITHOUT
PRESSURE TESTER DO NOT WASTE reusable coolant. If solution is
clean, drain coolant into a clean container for reuse.

WARNING:
DO NOT
REMOVE CYLINDER BLOCK DRAIN PLUGS
OR
LOOSEN RADIATOR DRAIN-

COCK
WITH
SYSTEM
HOT AND
UNDER PRES­

SURE.
SERIOUS BURNS FROM COOLANT
CAN

OCCUR.

Drain sufficient coolant to allow thermostat re­
moval. Refer to Thermostat Replacement. Disconnect
water pump drive belt. Add coolant to radiator to bring level to within 6.3
mm (1/4 in) of top of thermostat housing.

CAUTION:
Avoid
overheating.
Do not
operate
en­

gine
for an
excessive
period
of
time.
Open
drain-

cock
immediately
after
test
to
eliminate
boil
over.

Start engine and accelerate rapidly three times, to
approximately 3000 rpm while observing coolant. If
internal engine combustion gases% are leaking into
cooling system, bubbles will appear in coolant. If
bubbles do not appear, internal combustion gas leak­ age is not present.

COOLANT
RESERVE/0WERFL0W
SYSTEM
The coolant reserve/overflow system (Fig. 40 or 41)
works in conjunction with the radiator pressure cap.

•

IGNITION
SYSTEMS
8D
- 1
CONTENTS

page page
COMPONENT IDENTIFICATION/SYSTEM DIAGNOSTICS/SERVICE PROCEDURES
7
OPERATION
1
IGNITION SWITCH
25

COMPONENT REMOVAL/INSTALLATION
..... 18
SPECIFICATIONS
28

COMPONENT
IDENTIFICATION/SYSTEM OPERATION
INDEX
page

Automatic
Shut Down (ASD) Relay
1
Camshaft Position Sensor
2

Crankshaft Position Sensor
2

Distributors
3

Engine Coolant
Temperature
Sensor
...........
4

General
Information
1
page

Ignition
Coil
3
Intake
Manifold Charge
Air
Temperature
Sensor
. . 4

Manifold Absolute Pressure (MAP) Sensor
4
Powertrain
Control
Module (PCM)
. 5

Throttle
Position Sensor
5

GENERAL
INFORMATION
Throughout this group, references
are
made
to
par­
ticular vehicle models
by
alphabetical designation
or

by
the
particular vehicle nameplate.
A
chart showing a breakdown
of
alphabetical designations
is
included
in
the
Introduction group
at the
beginning
of
this
manual. 5.9L
gas
powered engines will
be
referred
to as ei­

ther: LDC (Light Duty Cycle),
or
HDC (Heavy Duty Cycle). This section
of the
group, Component Identifica­
tion/System Operation, will discuss ignition system operation
and
will identify ignition system compo­

nents.
For diagnostic procedures
and
adjustments, refer
to

the Diagnostics/Service Procedures section
of
this
group.
For removal
and
installation
of
ignition system
components, refer
to the
Component Removal/Instal­
lation section
of
this group. For other useful information, refer
to
On-Board
Di­

agnostics
in the
General Diagnosis sections
of
Group
14,
Fuel System
in
this manual. For operation
of the DRB II
Diagnostic Scan Tool,
refer
to the
appropriate Powertrain Diagnostic Proce­
dures service manual.
An Ignition specifications section
is
included
at the

end
of
this group.
A
general Maintenance Schedule (mileage intervals)
for
ignition related items
can be
found
in
Group
0,
Lubrication and Maintenance. This
schedule
can
also
be
found
in the
Owners Manual.

IGNITION
SYSTEMS
The ignition systems used
on all
engines
are
basi­
cally identical. Similarities
and
differences between
the systems will
be
discussed.
A sequential multi-port fuel injection system
is

used
on all gas
powered engines.
The ignition system
is
controlled
by the
powertrain
control module (PCM)
on all
engines.
The
PCM
was

formerly referred
to as the
SBEC
or
engine control­ ler.
The ignition system consists
of:

• Spark Plugs
• Ignition Coil
• Secondary Ignition Cables
• Ignition distributor. Contains rotor
and
camshaft
position sensor • Powertrain Control Module (PCM)
• Crankshaft Position Sensor

AUTOMATIC SHUT DOWN (ASD) RELAY
The automatic shut down (ASD) relay
is
located
in

the engine compartment (Fig.
1). As one of its
func­

tions,
the ASD
relay will supply battery voltage
to
the ignition coil.
The
ground circuit
for the
ASD
re­

lay
is
controlled
by the
powertrain control module (PCM).
The PCM
regulates
ASD
relay operation
by
switching
the
ground circuit on-and-off.

IGNITION
SYSTEMS

•

IGNITION
SYSTEMS
80 - 7
DIAGNOSTICS/SERW1CE
PROCEDURES

INDEX

page

Automatic Shut Down (ASD) Relay
7
Camshaft Position
Sensor
Test
...............
7

Crankshaft Position
Sensor
Test
8

Distributor
Cap
8

Distributor
Rotor
8
Engine
Coolant Temperature
Sensor
Test
10

General
Information
7

Ignition
Coil
8

Ignition
Secondary
Circuit
Diagnosis
10

GENERAL
INFORMATION
This section
of the
group, Diagnostics/Service Pro­
cedures, will discuss basic ignition system diagnos­
tics
and
service adjustments. For system operation
and
component identification,
refer
to the
Component Identification/System Opera­
tion section
of
this group. For removal
or
installation
of
ignition system com­
ponents, refer
to the
Component Removal/Installa­
tion section
of
this group. For other useful information, refer
to
On-Board
Di­

agnostics
in the
General Diagnosis sections
of
Group
14,
Fuel System
in
this manual. For operation
of the DRB II
Diagnostic Scan Tool,
refer
to the
appropriate Powertrain Diagnostic Proce­
dures service manual.

AUTOMATIC SHUT DOWN
(ASD)
RELAY
Refer
to
Relays—Operation/Testing
in the
Group

14,
Fuel System section
of
this service manual.

CAMSHAFT POSITION SENSOR TEST
The camshaft position sensor
is
located
in the
dis­
tributor
on all
engines. To perform
a
complete test
of
this sensor
and its

circuitry, refer
to the DRB II
diagnostic scan tool.
Also refer
to the
appropriate Powertrain Diagnostics
Procedures manual.
To
test
the
sensor only, refer
to

the following: For this test,
an
analog (non-digital) voltmeter
is needed.
Do not
remove
the
distributor connector from
the
distributor. Using small paper clips, insert
them into
the
backside
of the
distributor wire har­ ness connector
to
make contact with
the
terminals.
Be sure that
the
connector
is not
damaged when
in­
serting
the
paper clips. Attach voltmeter leads
to

these paper clips. (1) Connect
the
positive (
+
)
voltmeter lead into
the sensor output wire. This
is at
done
the
distribu­ tor wire harness connector.
For
wire identification,
refer
to
Group
8W,
Wiring Diagrams.
page

Ignition
Timing
12

Intake Manifold Charge
Air
Temperature
Sensor
Test
12

Manifold Absolute Pressure (MAP)
Sensor
Test
. 12

Oxygen
Sensor
Tests
17
Powertrain Control Module (PCM)
............
14

Spark
Plug Secondary Cables
16

Spark
Plugs
............................
14

Throttle
Position
Sensor
Test
17

(2) Connect
the
negative
(-)
voltmeter lead into
the

ground wire.
For
wire identification, refer
to
Group
8W, Wiring Diagrams.
(3)
Set the
voltmeter
to the 15
Volt
DC
scale. (4) Remove distributor
cap
from distributor
(two

screws). Rotate (crank)
the
engine until
the
distribu­
tor rotor
is
pointed towards
the
rear
of
vehicle.
The

movable pulse ring should
now be
within
the
sensor
pickup.
(5) Turn ignition
key to ON
position. Voltmeter
should read approximately
5.0
volts.
(6)
If
voltage
is not
present, check
the
voltmeter
leads
for a
good connection.
(7)
If
voltage
is
still
not
present, check
for
voltage
at
the
supply wire.
For
wire identification, refer
to

Group
8W,
Wiring Diagrams.
(8)
If
voltage
is not
present
at
supply wire, check
for voltage
at
pin-7
of
powertrain control module (PCM) 60-way connector. Leave
the PCM
connector
connected
for
this test. (9)
If
voltage
is
still
not
present, perform vehicle
test using
the DRB II
diagnostic scan tool. (10)
If
voltage
is
present
at
pin-7,
but not at the

supply wire: (a) Check continuity between
the
supply wire.
This
is
checked between
the
distributor connector and pin-7
at the PCM. If
continuity
is not
present,
repair
the
harness
as
necessary. (b) Check
for
continuity between
the
camshaft
position sensor output wire
and
pin-44
at the PCM.
If continuity
is not
present, repair
the
harness
as
necessary. (c) Check
for
continuity between
the
ground cir­
cuit wire
at the
distributor connector
and
ground.
If continuity
is not
present, repair
the
harness
as
necessary. (11) While observing
the
voltmeter, crank
the en­

gine with ignition switch.
The
voltmeter needle should fluctuate between
0 and 5
volts while
the en­

gine
is
cranking. This verifies that
the
camshaft
po­
sition sensor
in the
distributor
is
operating properly
and
a
sync pulse signal
is
being generated.

8D
- 14
IGNITION SYSTEMS

• (5) Test the MAP sensor ground circuit at sensor
connector terminal-A (Fig. 19) and PCM connector
terminal-4. Repair the wire harness if necessary.
(6) Test the MAP sensor ground circuit at the
PCM connector between terminal-4 and terminal-11
with an ohmmeter. If the ohmmeter indicates an
open circuit, inspect for a defective sensor ground
connection. Refer to Group 8W, Wiring for location of
this connection. If the ground connection is good, re­
place the PCM. If terminal-4 has a short circuit to 12 volts +, correct this condition before replacing the
PCM.

POWERTRAIN
CONTROL MODULE {PCM)
The PCM (formerly called the SBEC or engine -con­
troller) is located in the engine compartment (Fig.
20). DATA UNK CONTROL
CONNECTOR MODULE
J9314-164

Fig.
20 PCM Location The ignition system is controlled by the PCM.
For removal and installation of this component, re­
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 II scan tool.

SPARK
PLUGS
For spark plug removal, cleaning, gap adjustment
and installation, refer to the Component Removal/In­
stallation section of this group. Spark plug cable boot heat shields are pressed into
the cylinder head to surround each cable boot and
spark plug (Fig. 21). These shields protect the spark
plug boots from damage (due to intense engine heat
generated by the exhaust manifolds) and should not
be removed. After the spark plug cable has been in­ stalled, the lip of the cable boot should have a small
air gap to the top of the heat shield (Fig. 21). 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
Fig.
21 Heat
Shields

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 indi­
cates that a problem exists in the corresponding
cylinder. Replace spark plugs at the intervals recom­
mended in the maintenance chart in Group 0, Lubri­
cation 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.

CONDITION
NORMAL 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. 22). 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.
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 combustion chamber. Spark plug performance is not affected by MMT deposits.

COLD
FOULING/CARBON FOULING
Cold fouling is sometimes referred to as carbon
fouling. The deposits that cause cold fouling are ba-

•

IGNITION
SYSTEMS
8D - 15 J908D-15

Fig.
22 Normal Operation and Cold (Carbon) Fouling
sically carbon (Fig. 22). A dry, black deposit on one
or two plugs in a set may be caused by sticking
valves or defective spark plug cables. Cold (carbon)
fouling of the entire set of spark plugs may be caused
by a clogged air filter or .repeated short operating
times (short trips).

ELECTRODE GAP BRIDGIMG
Electrode gap bridging may be traced to loose de­
posits in the combustion chamber. These deposits ac­ cumulate on the spark plugs during continuous stop-
and-go driving. When the engine is suddenly
subjected to a high torque load, deposits partially liq­
uefy and bridge the gap between electrodes (Fig. 28).
This short circuits the electrodes. Spark plugs with electrode gap bridging can be cleaned using standard
procedures.

GROUND
ELECTRODE

J908D-11
Fig. 23 Electrode Gap Bridging

SCAVENGER
DEPOSITS
Fuel scavenger deposits may be either white or yel­
low (Fig. 24). They may appear to be harmful, but
this is a normal condition caused by chemical addi­
tives in certain fuels. These additives are designed to change the chemical nature of deposits and decrease
spark plug misfire tendencies. Notice that accumula­
tion on the ground electrode and shell area may be
heavy, but the deposits are easily removed. Spark
plugs with scavenger deposits can be considered nor­ mal in condition and can be cleaned using standard
procedures.

GROUND
ELECTRODE
COVERED

J908D-12

Fig.
24
Scavenger
Deposits

CHIPPED ELECTRODE
INSULATOR
A chipped electrode insulator usually results from
bending the center electrode while adjusting the spark plug electrode gap. Under certain conditions, severe detonation can also separate the insulator
from the center electrode (Fig. 25). Spark plugs with
this condition must be replaced.
GROUND

J908D-13

Fig.
25
Chipped
Electrode Insulator
PREIGNITION
DAMAGE

Preignition damage is usually caused by excessive
combustion chamber temperature. The center elec­
trode dissolves first and the ground electrode dis­ solves somewhat latter (Fig. 26). Insulators appear
relatively deposit free. Determine if the spark plug
has the correct heat range rating for the engine. De­
termine if ignition timing is over advanced, or if

8D
- 16
IGNITION
SYSTEMS

• other operating conditions are causing engine over­
heating. (The heat range rating refers to the operat­
ing temperature of a particular type spark plug.
Spark plugs are designed to operate within specific
temperature ranges. This depends upon the thickness and length of the center electrodes porcelain insula­
tor.)

GROUND

ELECTRODE
CENTER

ELECTRODE

DISSOLVED

J908D-14 Fig. 26 Preignition Damage

SPARK
PLUG
OVERHEATING
Overheating is indicated by a white or gray center
electrode insulator that also appears blistered (Fig.
27).
The increase in electrode gap will be consider­
ably in excess of 0.001 inch per 1000 miles of opera­
tion. This suggests that a plug with a cooler heat
range rating should be used. Over advanced ignition
timing, detonation and cooling system malfunctions can also cause spark plug overheating.

BLISTERED

WHITE
OR
J908D-16
Fig. 27 Spark Plug Overheating

SPARK
PLUG
SECONDARY
CABLES
Spark plug heat shields are pressed into the cylin­
der head to surround each spark plug cable boot and spark plug (Fig. 28). These shields protect the spark
plug boots from damage (due to intense engine heat
generated by the exhaust manifolds) and should not be removed. After the spark plug cable has been in­
stalled, the lip of the cable boot should have a small
air gap to the top of the heat shield (Fig. 28).

Fig.
28 Heat
Shields
TESTING

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 in resistance. The cables provide suppression of radio frequency emissions from the ignition system.
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 in 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 in 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. If 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
cause
possible
heat
damage
to the
catalytic converter. Total test
time
must
not exceed
ten
minutes.

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. If cables are cracked