CHRYSLER VOYAGER 1996 Service Manual

All engines use resistor spark plugs. They have
resistance values ranging from 6,000 to 20,000 ohms
when checked with at least a 1000 volt spark plug
tester.
Do not use an ohm meter to check the resis-
tance of the spark plugs. This will give an inac-
curate reading.
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
Group O - Lubrication and Maintenance.
Spark plugs that have low mileage may be cleaned
and reused if not otherwise defective, carbon or oil
fouled. Refer to the Spark Plug Condition section of
this group.
The spark plugs are double platinum and have a
recommended service life of 100,000 miles for normal
driving conditions per schedule A in this manual. The
spark plugs have a recommended service life of
75,000 miles for serve driving conditions per schedule
B in this manual. A thin platinum pad is welded to
both electrode ends as show in (Fig. 3). Extreme care
must be used to prevent spark plug cross threading,
mis-gaping and ceramic insulator damage during
plug removal and installation.
CAUTION: Never attempt to file the electrodes or
use a wire brush for cleaning platinum plugs. This
would damage the platinum pads which would
shorten spark plug life.
Apply a very small amount of anti-seize compound
to the threads when reinstalling the vehicle's original
spark plugs that have been determined good.Do not
apply anti-seize compound to new spark plugs.
NOTE: Anti-seize compound is electrically conduc-
tive and can cause engine misfires if not applied
correctly. It is extremely important that the anti-
seize compound doesn't make contact with the
spark plug electrodes or ceramic insulator.
Never force a gap gauge between the platinum
electrodes or adjust the gap on platinum spark plugs
without reading the 3.3/3.8L Spark Plug Gap Mea-
surement procedures in this section.
Always tighten spark plugs to the specified torque.
Over tightening can cause distortion resulting in a
change in the spark plug gap. Overtightening can
also damage the cylinder head. Tighten spark plugs
to 28 N´m (20 ft. lbs.) torque.
Due to the engine packaging environment for the
3.3/3.8L engines, extreme care should be used wheninstalling the spark plugs to avoid cross threading
problems.
3.3/3.8L SPARK PLUG GAP MEASUREMENT
CAUTION: The Platinum pads can be damaged dur-
ing the measurement of checking the gap if extreme
care is not used.
²USE ONLY A TAPER GAP GAUGE (Fig. 2)
²Never force the gap gauge through the platinum
pads. Only apply enough force until resistance is felt.
²Never use a wire brush or spark plug cleaner
machine to clean platinum spark plugs
²Use an OSHA approved air nozzle when drying
gas fouled spark plugs.
If gap adjustment is required of platinum plug,
bend only the ground electrode. DO NOT TOUCH
the platinum pads. Use only a proper gapping tool
and check with a taper gap gauge.
CAUTION: Cleaning of the platinum plug may dam-
age the platinum tip.
SPARK PLUG CABLE
Spark Plug cables are sometimes referred to as
secondary ignition wires. The wires transfer electri-
cal current from the ignition coil pack, distributor
(3.0L), to individual spark plugs at each cylinder. The
resistive spark plug cables are of nonmetallic con-
struction. The cables provide suppression of radio fre-
quency emissions from the ignition system.
Check the spark plug cable connections for good
contact at the coil, distributor cap towers (3.0L), and
spark plugs. Terminals should be fully seated. The
insulators should be in good condition and should fit
tightly on the coil, distributor (3.0L) and spark plugs.
Spark plug cables with insulators that are cracked or
torn must be replaced.
Fig. 3 Platinum Pads
NSIGNITION SYSTEM 8D - 3
GENERAL INFORMATION (Continued)

Clean Spark Plug cables with a cloth moistened
with a non-flammable solvent. Wipe the cables dry.
Check for brittle or cracked insulation.
SPARK PLUG CABLESÐ3.3/3.8L
The spark plug cables and spark plug boots are
made from high temperature silicone materials. The
spark plug boots utilize metal heat shields for ther-
mal protection from the exhaust manifold. The heat
shields slide over the spark plug boots. The notches
on the heat shields ensure the spark plug boot and
shield twist together during spark plug boot removal.
They also identify proper heat shield installation on
the boot for service.Refer to 3.3/3.8L Spark Plug
Cable removal and installation.All spark plug
cable leads are properly identified with cylinder num-
bers. The inside of the spark plug boot is coated with
a special high temperature silicone grease for greater
sealing and to minimize boot bonding to the spark
plug insulator. The convoluted tubing on the rear
plug cables are made of a high temperature plastic
material. Under normal driving conditions, the spark
plug cables have a recommended service life of a
100,000 miles. The spark plugs have a recommended
service life of 75,000 miles for severe driving condi-
tions per schedule B in this manual.
The spark plug heat shield can be reused if an
ignition cable is replaced due to failure. Never reuse
heat shield's that have heat shield anti-twist, side or
spark plug attachment tabs bent or missing. Ensure
that the heat shield is properly attached to the spark
plug to avoid RFI problems. The bottom of the spark
plug heat shield must make contact with the spark
plug hex.
The front ignition cables must not make contact
with the oil dip stick tube and #5 cable must not
touch the coil mounting bolt to avoid abrasion/dielec-
tric failures.
IGNITION COIL
WARNING: THE DIRECT IGNITION SYSTEM GEN-
ERATES APPROXIMATELY 40,000 VOLTS. PER-
SONAL INJURY COULD RESULT FROM CONTACT
WITH THIS SYSTEM.
The ignition coil assembly consists of 3 indepen-
dent coils molded together (Fig. 4). The coil assembly
is mounted on the intake manifold. Spark plug cables
route to each cylinder from the coil. The coil fires two
spark plugs every power stroke. One plug is the cyl-
inder under compression, the other cylinder fires on
the exhaust stroke. The Powertrain Control Module
(PCM) determines which of the coils to charge and
fire at the correct time.
Coil 1 fires cylinders 1 and 4, coil 2 fires cylinders
2 and 5, coil 3 fires cylinders 3 and 6.The Auto Shutdown (ASD) relay provides battery
voltage to the ignition coil. The PCM provides a
ground contact (circuit) for energizing the coil. When
the PCM breaks the contact, the energy in the coil
primary transfers to the secondary causing the
spark. The PCM will de-energize the ASD relay if it
does not receive the crankshaft position sensor and
camshaft position sensor inputs. Refer to Auto Shut-
down (ASD) RelayÐPCM Output, in this section for
relay operation.
AUTOMATIC SHUTDOWN (ASD) RELAY
The Powertrain Control Module (PCM) operates
the Auto Shutdown (ASD) relay by switching the
ground path on and off.
The ASD relay supplies battery voltage to the fuel
injectors, electronic ignition coil and the heating ele-
ments in the oxygen sensors.
The PCM controls the relay by switching the
ground path for the solenoid side of the relay on and
off. The PCM turns the ground path off when the
ignition switch is in the Off position unless the 02
Heater Monitor test is being run. Refer to Group 25,
On-Board Diagnostics. When the ignition switch is in
the On or Crank position, the PCM monitors the
crankshaft position sensor and camshaft position sen-
sor signals to determine engine speed and ignition
timing (coil dwell). If the PCM does not receive the
crankshaft position sensor and camshaft position sen-
sor signals when the ignition switch is in the Run
position, it will de-energize the ASD relay.
The ASD relay is located in the Power Distribution
Center (PDC). The PDC is located on the driver's
side inner fender well (Fig. 5). A label on the under-
side of the PDC cover identifies the relays and fuses
in the PDC.
Fig. 4 Ignition Coil Pack
8D - 4 IGNITION SYSTEMNS
GENERAL INFORMATION (Continued)

CRANKSHAFT POSITION SENSOR
The crankshaft position sensor detects slots cut
into the transmission driveplate extension (Fig. 6).
There are 3 sets of slots. Each set contains 4 slots,
for a total of 12 slots (Fig. 7). Basic timing is set by
the position of the last slot in each group. Once the
Powertrain Control Module (PCM) senses the last
slot, it determines crankshaft position (which piston
will next be at TDC) from the camshaft position sen-
sor input. The 4 pulses generated by the crankshaft
position sensor represent the 69É, 49É, 29É, and 9É
BTDC marks. It may take the PCM one engine rev-
olution to determine crankshaft position.
The PCM uses crankshaft position reference to
determine injector sequence, ignition timing and the
presence of misfire. Once the PCM determines crank-
shaft position, it begins energizing the injectors in
sequence.The crankshaft sensor is located on the passengers
side of the transmission housing, above the differen-
tial housing (Fig. 8). The bottom of the sensor is posi-
tioned next to the drive plate.
CAMSHAFT POSITION SENSOR
The camshaft position sensor provides cylinder
identification to the Powertrain Control Module
(PCM) (Fig. 9). The sensor generates pulses as
groups of notches on the camshaft sprocket pass
underneath it (Fig. 10). The PCM keeps track of
crankshaft rotation and identifies each cylinder by
the pulses generated by the notches on the camshaft
sprocket. Four crankshaft pulses follow each group of
camshaft pulses.
When the PCM receives 2 cam pulses followed by
the long flat spot on the camshaft sprocket, it knows
that the crankshaft timing marks for cylinder 1 are
next (on driveplate). When the PCM receives one
camshaft pulse after the long flat spot on the
sprocket, cylinder number 2 crankshaft timing marks
are next. After 3 camshaft pulses, the PCM knows
Fig. 5 Power Distribution Center
Fig. 6 Crankshaft Position Sensor
Fig. 7 Timing Slots
Fig. 8 Crankshaft Position Sensor Location
NSIGNITION SYSTEM 8D - 5
GENERAL INFORMATION (Continued)

cylinder 4 crankshaft timing marks follow. One cam-
shaft pulse after the 3 pulses indicates cylinder 5.
The 2 camshaft pulses after cylinder 5 signals cylin-
der 6 (Fig. 10). The PCM can synchronize on cylin-
ders1or4.
When metal aligns with the sensor, voltage goes
low (less than 0.3 volts). When a notch aligns with
the sensor, voltage switches high (5.0 volts). As a
group of notches pass under the sensor, the voltage
switches from low (metal) to high (notch) then back
to low. The number of notches determine the amount
of pulses. If available, an oscilloscope can display the
square wave patterns of each timing event.
Top Dead Center (TDC) does not occur when
notches on the camshaft sprocket pass below the cyl-
inder. TDC occurs after the camshaft pulse (or
pulses) and after the 4 crankshaft pulses associated
with the particular cylinder. The arrows and cylinder
call outs on Figure 4 represent which cylinder the
flat spot and notches identify, they do not indicate
TDC position.
The camshaft position sensor is mounted in the
front of the timing case cover (Fig. 11).
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
The MAP sensor reacts to absolute pressure in the
intake manifold and provides an input voltage to the
Powertrain Control Module (PCM). As engine load
changes, manifold pressure varies. The changes in
engine load cause the MAP sensors resistance to
change. The change in MAP sensor resistance results
in a different input voltage to the PCM.
The input voltage level supplies the PCM with
information relating to ambient barometric pressure
during engine start-up (cranking) and engine load
while its operating. Based on MAP sensor voltage
and inputs from other sensors, the PCM adjusts
spark advance and the air-fuel mixture.
ENGINE COOLANT TEMPERATURE (ECT) SENSOR
The ECT sensor is located next to the thermostat
housing (Fig. 12). The sensor provides an input volt-
age to the Powertrain Control Module (PCM). Thesensor is a variable resistance (thermistor) with a
range of -40ÉF to 265ÉF. As coolant temperature var-
ies, the sensors resistance changes, resulting in a dif-
ferent input voltage to the PCM.
The PCM contains different spark advance sched-
ules for cold and warm engine operation. The sched-
ules reduce engine emission and improve driveability.
When the engine is cold, the PCM will demand
slightly richer air-fuel mixtures and higher idle
speeds until normal operating temperatures are
reached.
The ECT sensor input is also used for cooling fan
control.
Fig. 9 Camshaft Position Sensor
Fig. 10 Camshaft Sprocket
Fig. 11 Camshaft Position Sensor Location
8D - 6 IGNITION SYSTEMNS
GENERAL INFORMATION (Continued)

THROTTLE POSITION SENSOR (TPS)
The TPS mounts to the side of the throttle body
(Fig. 13).
The TPS connects to the throttle blade shaft. The
TPS is a variable resistor that provides the Power-
train Control Module (PCM) with an input signal
(voltage). The signal represents throttle blade posi-
tion. As the position of the throttle blade changes,
the resistance of the TPS changes.
The PCM supplies approximately 5 volts to the
TPS. The TPS output voltage (input signal to the
powertrain control module) represents throttle blade
position. The TPS output voltage to the PCM varies
from approximately 0.40 volt at minimum throttle
opening (idle) to a maximum of 3.80 volts at wide
open throttle.
Along with inputs from other sensors, the PCM
uses the TPS input to determine current engine oper-
ating conditions. The PCM also adjusts fuel injector
pulse width and ignition timing based on these
inputs.
LOCK KEY CYLINDER
The lock cylinder is inserted in the end of the
housing opposite the ignition switch. The ignition key
rotates the cylinder to 5 different detents (Fig. 14):
²Accessory
²Off (lock)
²Unlock
²On/Run
²Start
KNOCK SENSOR
The knock sensor threads into the side of the cyl-
inder block in front of the starter motor. When the
knock sensor detects a knock in one of the cylinders,
it sends an input signal to the PCM. In response, the
PCM retards ignition timing for all cylinders by a
scheduled amount.
Knock sensors contain a piezoelectric material
which constantly vibrates and sends an input voltage
(signal) to the PCM while the engine operates. As the
intensity of the crystal's vibration increase, the knock
sensor output voltage also increases.
Fig. 12 Engine Coolant Temperature SensorÐ3.3/
3.8LFig. 13 Throttle Position Sensor and Idle Air Control
Motor
Fig. 14 Ignition Lock Cylinder Detents
NSIGNITION SYSTEM 8D - 7
GENERAL INFORMATION (Continued)

NOTE: Over or under tightening effects knock sen-
sor performance, possibly causing improper spark
control.
DIAGNOSIS AND TESTING
TESTING FOR SPARK AT COILÐ2.4/3.3/3.8L
ENGINES
WARNING: THE DIRECT IGNITION SYSTEMS GEN-
ERATES APPROXIMATELY 40,000 VOLTS. PER-
SONAL INJURY COULD RESULT FROM CONTACT
WITH THIS SYSTEM.
The coil pack contains independent coils. Each coil
must be checked individually.
CAUTION: Spark plug wire damage may occur if
the spark plug is moved more than 1/4 inch away
from the engine ground.
CAUTION: Do not leave any one spark plug cable
disconnected any longer than 30 seconds or possi-
ble heat damage to catalytic converter will occur.
CAUTION: Test must be performed at idle and in
park only with the parking brake on.
Use a new spark plug and spark plug cable
for the following test.
(1) Insert a new spark plug into the new spark
plug boot. Ground the plug to the engine (Fig. 15).
Do not hold with your hand.
(2) Starting with coil insulator #1, remove it from
the DIS coil.(3) Plug the test spark plug cable onto #1 coil
tower. Make sure a good connection is made; there
should be a click sound.
(4) Crank the engine and look for spark across the
electrodes of the spark plug.
CAUTION: Always install the cable back on the coil
tower after testing to avoid damage to the coil and
catalytic converter.
(5) Repeat the above test for the remaining coils. If
there is no spark during all cylinder tests, proceed to
the Failure To Start Test.
(6) If one or more tests indicate irregular, weak, or
no spark, proceed to Check Coil Test.
TESTING FOR SPARK AT COILÐ3.0L
WARNING: APPLY PARKING BRAKE AND/OR
BLOCK THE WHEELS BEFORE PERFORMING ANY
TEST WITH THE ENGINE RUNNING.
CAUTION: Spark plug cables may be damaged if
this test is performed with more than 1/4 inch clear-
ance between the cable and engine ground.
Remove the coil secondary cable from the distribu-
tor cap. Hold the end of cable about 6 mm (1/4-inch)
away from a good engine ground using non-conduc-
tive ignition pliers (Fig. 16). Crank the engine and
inspect for spark at the coil secondary cable.
There must be a constant spark at the coil second-
ary cable. If spark is not constant or there is no
spark, proceed to the failure to start test. If the
spark is constant, continue to crank engine and,
while slowly moving coil secondary cable away from
ground, look for arcing at the coil tower. If arcing
occurs at the tower, replace the coil.
If a constant spark is present and no arcing occurs
at the coil tower, the ignition system is producing the
necessary high secondary voltage. However, make
Fig. 15 Testing For Spark
Fig. 16 Checking for Spark
8D - 8 IGNITION SYSTEMNS
GENERAL INFORMATION (Continued)

sure that the spark plugs are firing. Inspect the dis-
tributor rotor, cap, spark plug cables, and spark
plugs. If they are in proper working order, the igni-
tion system is not the reason why the engine will not
start. Inspect the fuel system and engine for proper
operation.
CHECK COIL TESTÐ2.4L
Coil one fires cylinders 1 and 4, coil two fires
cylinders 2 and 3. Each coil tower is labeled
with the number of the corresponding cylinder.
(1) Remove ignition cables and measure the resis-
tance of the cables. Resistance must be within the
range shown in the Cable Resistance Chart in Spec-
ifications. Replace any cable not within tolerance.
(2) Disconnect the electrical connector from the
coil pack.
(3) Measure the primary resistance of each coil. At
the coil, connect an ohmmeter between the B+ pin
and the pin corresponding to the cylinders in ques-
tion (Fig. 17). Resistance on the primary side of each
coil should be 0.45 - 0.65 ohm at (70É to 80É F).
Replace the coil if resistance is not within tolerance.
(4) Remove ignition cables from the secondary tow-
ers of the coil. Measure the secondary resistance of
the coil between the towers of each individual coil
(Fig. 18). Secondary resistance should be 7,000 to
15,800 ohms. Replace the coil if resistance is not
within tolerance.
CHECK COIL TESTÐ3.3/3.8L
Coil 1 fires cylinders 1 and 4, coil 2 fires cyl-
inders 2 and 5, and coil 3 fires cylinders 3 and
6. Each coil tower is labeled with the number of
the corresponding cylinder.
(1) Disconnect the electrical connector from the
coil pack (Fig. 19).
(2) Measure the primary resistance of each coil. At
the coil, connect an ohmmeter between the B+ pinand the pin corresponding to the cylinders in ques-
tion (Fig. 20). Resistance on the primary side of each
coil should be 0.45 - 0.65 ohm at 21É to 27ÉC (70É to
80ÉF). A coil that has not been allowed to cool off,
would result in inaccurate measurement results.
Replace the coil if resistance is not within tolerance.
Fig. 17 Terminal Identification
Fig. 18 Checking Ignition Coil Secondary
Resistance
Fig. 19 Ignition Coil Electrical Connector
Fig. 20 Ignition Coil Terminal Identification
NSIGNITION SYSTEM 8D - 9
DIAGNOSIS AND TESTING (Continued)

(3) Remove ignition cables from the secondary tow-
ers of the coil. Measure the secondary resistance of
the coil between the towers of each individual coil
(Fig. 21). Secondary resistance should be 7,000 to
15,800 ohms. Replace the coil if resistance is not
within tolerance.
FAILURE TO START TEST
This no-start test checks the camshaft position sen-
sor and crankshaft position sensor.
The Powertrain Control Module (PCM) supplies 8
volts to the camshaft position sensor and crankshaft
position sensor through one circuit. If the 8 volt sup-
ply circuit shorts to ground, neither sensor will pro-
duce a signal (output voltage to the PCM).
When the ignition key is turned and left in the On
position, the PCM automatically energizes the Auto
Shutdown (ASD) relay. However, the controller de-en-
ergizes the relay within one second because it has
not received a camshaft position sensor signal indi-
cating engine rotation.
During cranking, the ASD relay will not energize
until the PCM receives a camshaft position sensor
signal. Secondly, the ASD relay remains energized
only if the controller senses a crankshaft position
sensor signal immediately after detecting the cam-
shaft position sensor signal.
(1) Check battery voltage. Voltage should be
approximately 12.66 volts or higher to perform fail-
ure to start test.
(2) Disconnect the harness connector from the coil
pack.
(3) Connect a test light to the B+ (battery voltage)
terminal of the coil electrical connector and ground
as shown in (Fig. 22). The B+ wire for the DIS coil is
dark green with an orange tracer.Do not spread
the terminal with the test light probe.(4) Turn the ignition key to theON position.The
test light should flash On and then Off.Do not turn
the Key to off position, leave it in the On posi-
tion.
(a) If the test light flashes momentarily, the
PCM grounded the Auto Shutdown (ASD) relay.
Proceed to step 5.
(b) If the test light did not flash, the ASD relay
did not energize. The cause is either the relay or
one of the relay circuits. Use the DRB scan tool to
test the ASD relay and circuits. Refer to the appro-
priate Powertrain Diagnostics Procedure Manual.
Refer to the wiring diagrams section for circuit
information.
(5) Crank the engine. (If the key was placed in the
off position after step 4, place the key in the On posi-
tion before cranking. Wait for the test light to flash
once, then crank the engine.)
(6) If the test light momentarily flashes during
cranking, the PCM is not receiving a crankshaft posi-
tion sensor signal. Use the DRB scan tool to test the
crankshaft position sensor and sensor circuits. Refer
to the appropriate Powertrain Diagnostics Procedure
Manual. Refer to the wiring diagrams section for cir-
cuit information.
(7) If the test light did not flash during cranking,
unplug the crankshaft position sensor connector.
Turn the ignition key to the off position. Turn the
key to the On position, wait for the test light to
momentarily flash once, then crank the engine. If the
test light momentarily flashes, the crankshaft posi-
tion sensor is shorted and must be replaced. If the
light did not flash, the cause of the no-start is in
Fig. 21 Checking Ignition Coil Secondary
ResistanceFig. 22 Ignition Coil Engine Harness Connector
8D - 10 IGNITION SYSTEMNS
DIAGNOSIS AND TESTING (Continued)

either the crankshaft position sensor/camshaft posi-
tion sensor 8 volt supply circuit, or the camshaft
position sensor output or ground circuits. Use the
DRB scan tool to test the camshaft position sensor
and the sensor circuits. Refer to the appropriate Pow-
ertrain Diagnostics Procedure Manual. Refer to the
wiring diagrams section for circuit information.
IGNITION TIMING PROCEDURE
The engines for this vehicle, use a fixed ignition
system. The PCM regulates ignition timing. Basic
ignition timing is not adjustable.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
TEST
Refer to Group 14, Fuel System for Diagnosis and
Testing.
CAMSHAFT POSITION SENSOR AND CRANKSHAFT
POSITION SENSOR
The output voltage of a properly operating cam-
shaft position sensor or crankshaft position sensor
switches from high (5.0 volts) to low (0.3 volts). By
connecting an Moper Diagonostic System (MDS) and
engine analyzer to the vehicle, technicians can view
the square wave pattern.
ENGINE COOLANT TEMPERATURE SENSOR
Refer to Group 14, Fuel System for Diagnosis and
Testing.
INTAKE AIR TEMPERATURE SENSOR
Refer to Group 14, Fuel System, for Diagnosis and
Testing.
SPARK PLUG CONDITION
NORMAL OPERATING CONDITIONS
The few deposits present will be probably light tan
or slightly gray in color with most grades of commer-
cial gasoline (Fig. 23). There will not be evidence of
electrode burning. Gap growth will not average more
than approximately 0.025 mm (.001 in) per 1600 km
(1000 miles) of operation for non platinum spark
plugs. Non-platnium spark plugs that have normal
wear can usually be cleaned, have the electrodes filed
and regapped, and then reinstalled.
CAUTION: Never attempt to file the electrodes or
use a wire brush for cleaning platinum spark plugs.
This would damage the platinum pads which would
shorten spark plug life.
Some fuel refiners in several areas of the United
States have introduced a manganese additive (MMT)
for unleaded fuel. During combustion, fuel with MMT
may coat the entire tip of the spark plug with a rustcolored deposit. The rust color deposits can be misdi-
agnosed 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 because the deposits that cause cold fouling
are basically carbon (Fig. 23). A dry, black deposit on
one or two plugs in a set may be caused by sticking
valves or misfire conditions. Cold (carbon) fouling of
the entire set may be caused by a clogged air cleaner.
Cold fouling is normal after short operating peri-
ods. The spark plugs do not reach a high enough
operating temperature during short operating peri-
ods.Replace carbon fouled plugs with new
spark plugs.
FUEL FOULING
A spark plug that is coated with excessive wet fuel
is called fuel fouled. This condition is normally
observed during hard start periods.Clean fuel
fouled spark plugs with compressed air and
reinstall them in the engine.
OIL FOULING
A spark plug that is coated with excessive wet oil
is oil fouled. In older engines, wet fouling can be
caused by worn rings or excessive cylinder wear.
Break-in fouling of new engines may occur before
normal oil control is achieved.Replace oil fouled
spark plugs with new ones.
OIL OR ASH ENCRUSTED
If one or more plugs are oil or ash encrusted, eval-
uate the engine for the cause of oil entering the com-
bustion chambers (Fig. 24). Sometimes fuel additives
can cause ash encrustation on an entire set of spark
Fig. 23 Normal Operation and Cold (Carbon) Fouling
NSIGNITION SYSTEM 8D - 11
DIAGNOSIS AND TESTING (Continued)

plugs.Ash encrusted spark plugs can be cleaned
and reused.
HIGH SPEED MISS
When replacing spark plugs because of a high
speed miss condition;wide open throttle opera-
tion should be avoided for approximately 80 km
(50 miles) after installation of new plugs.This
will allow deposit shifting in the combustion chamber
to take place gradually and avoid plug destroying
splash fouling shortly after the plug change.
ELECTRODE GAP BRIDGING
Loose deposits in the combustion chamber can
cause electrode gap bridging. The deposits accumu-
late on the spark 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 between the electrodes
(Fig. 25). This short circuits the electrodes.Spark
plugs with electrode gap bridging can be
cleaned and reused.
SCAVENGER DEPOSITS
Fuel scavenger deposits may be either white or yel-
low (Fig. 26). They may appear to be harmful, but
are a normal condition caused by chemical additives
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 consid-
ered normal in condition, cleaned and reused.
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 also can separate the insulator
from the center electrode (Fig. 27).Spark plugs
with chipped electrode insulators must be
replaced.
PREIGNITION DAMAGE
Excessive combustion chamber temperature can
cause preignition damage. First, the center electrode
dissolves and the ground electrode dissolves some-
what later (Fig. 28). Insulators appear relatively
deposit free. Determine if the spark plugs are the
correct type, as specified on the VECI label, or if
other operating conditions are causing engine over-
heating.
SPARK PLUG OVERHEATING
Overheating is indicated by a white or gray center
electrode insulator that also appears blistered (Fig.
Fig. 24 Oil or Ash Encrusted
Fig. 25 Electrode Gap Bridging
Fig. 26 Scavenger Deposits
8D - 12 IGNITION SYSTEMNS
DIAGNOSIS AND TESTING (Continued)