1999 DODGE NEON check engine

performed at each (- ground) connection in this cir-
cuit to locate the excessive resistance.
(7) Testing (+ positive) circuitry:
(a) Touch the positive lead of voltmeter directly
to battery negativePOST.
(b) Touch the negative lead of voltmeter to the
ground terminal stud on the generator case (not
the terminal mounting nut). Voltage should be no
higher than 0.3 volts. If voltage is higher than 0.3
volts, touch test lead to terminal mounting stud
nut and then to the wiring connector. If voltage is
now below 0.3 volts, look for dirty, loose or poor
connection at this point. A voltage drop test may be
performed at each (+ positive) connection in this
circuit to locate the excessive resistance. This test
can also be performed between the generator case
and the engine. If test voltage is higher than 0.3
volts, check for corrosion at generator mounting
points or loose generator mounting.
CURRENT OUTPUT TEST
The current output test will determine if the
charging system can deliver its minimum test cur-
rent (amperage) output. Refer to the Specifications
section at the end of this group for minimum test
current (amperage) requirements.
The first part of this test will determine the com-
bined amperage output of both the generator and the
Electronic Voltage Regulator (EVR) circuitry.
PREPARATION
(1) Determine if any Diagnostic Trouble Codes
(DTC) exist. To determine a DTC, refer to On-Board
Diagnostics in this group. For repair, refer to the
appropriate Powertrain Diagnostic Procedures man-
ual.
(2) Before starting test, make sure battery is in
good condition and is fully-charged. See Group 8A,
Battery for more information.
(3) Check condition of battery cables at battery.
Clean if necessary.
(4) Perform the Voltage Drop Test. This will
ensure clean and tight generator/battery electrical
connections.
(5) Be sure the generator drive belt is properly
tensioned. Refer to Group 7, Cooling System for
information.
(6) A volt/amp tester equipped with both a battery
load control (carbon pile rheostat) and an inductive-
type pickup clamp (ammeter probe) will be used for
this test. Refer to operating instructions supplied
with tester. When using a tester equipped with an
inductive-type clamp, removal of wiring at the gener-
ator will not be necessary.
(7) Start the engine and allow it to reach operating
temperature.
(8) Shut engine off.(9) Turn off all electrical accessories and all vehicle
lighting.
(10) Connect the volt/amp tester leads to the bat-
tery. Be sure the carbon pile rheostat control is in the
OPEN or OFF position before connecting leads. See
Load Test in Group 8A, Battery for more information.
Also refer to the operating instructions supplied with
test equipment.
(11) Connect the inductive clamp (ammeter probe).
Refer to the operating instructions supplied with test
equipment.
(12) If volt/amp tester is not equipped with an
engine tachometer, connect a separate tachometer to
the engine.
TEST
(1) Perform the previous test Preparation.
(2) Fully engage the parking brake.
(3) Start engine.
(4) Bring engine speed to 2500 rpm.
(5) With engine speed held at 2500 rpm, slowly
adjust the rheostat control (load) on the tester to
obtain the highest amperage reading. Do not allow
voltage to drop below 12 volts. Record the reading.
This load test must be performed within 15 sec-
onds to prevent damage to test equipment.On
certain brands of test equipment, this load will be
applied automatically. Refer to the operating manual
supplied with test equipment.
(6) The ammeter reading must meet the Minimum
Test Amps specifications as displayed in the Genera-
tor Ratings chart. This can be found in the Specifica-
tions section at the end of this group. A label stating
a part reference number is attached to the generator
case. On some engines this label may be located on
the bottom of the case. Compare this reference num-
ber to the Generator Ratings chart.
(7) Rotate the load control to the OFF position.
(8) Continue holding engine speed at 2500. If EVR
circuitry is OK, amperage should drop below 15±20
amps. With all electrical accessories and vehicle
lighting off, this could take several minutes of engine
operation. If amperage did not drop, refer to the
appropriate Powertrain Diagnostic Procedures man-
ual for testing.
(9) Remove volt/amp tester.
If minimum amperage could not be met, refer to
the appropriate Powertrain Diagnostic Procedures
manual for testing.
BATTERY TEMPERATURE SENSOR
To perform a complete test of this sensor and its
circuitry, refer to the appropriate Powertrain Diag-
nostic Procedures manual. To test the sensor only,
refer to the following:
(1) The sensor is located under the battery and is
attached to the battery tray (Fig. 5). A two-wire pig-
8C - 8 CHARGING SYSTEMPL
DIAGNOSIS AND TESTING (Continued)

tail harness is attached directly to the sensor. The
opposite end of this harness connects the sensor to
the engine wiring harness.
(2) Disconnect the two-wire pigtail harness from
the engine harness.
(3) Attach ohmmeter leads to the wire terminals of
the pigtail harness.
(4) At room temperature of 25É C (75±80É F), an
ohmmeter reading of 9,000 (9K) to 11,000 (11K) ohms
should be observed.
(5) If reading is above or below the specification,
replace the sensor.
(6) Refer to the Removal and Installation section
for procedures.
ON-BOARD DIAGNOSTIC SYSTEM TEST
GENERAL INFORMATION
The Powertrain Control Module (PCM) monitors
critical input and output circuits of the charging sys-
tem, making sure they are operational. A Diagnostic
Trouble Code (DTC) is assigned to each input and
output circuit monitored by the OBD system. Some
circuits are checked continuously and some are
checked only under certain conditions.
If the OBD system senses that a monitored circuit
is bad, it will put a DTC into electronic memory. The
DTC will stay in electronic memory as long as the
circuit continues to be bad. The PCM is programmed
to clear the memory after 50 engine starts if the
problem does not occur again.
DIAGNOSTIC TROUBLE CODES
Refer to Group 25, On Board Diagnostic for more
information. A DTC description can be read using the
DRB scan tool. Refer to the appropriate Powertrain
Diagnostic Procedures manual for information.
A DTC does not identify which component in a cir-
cuit is bad. Thus, a DTC should be treated as asymptom, not as the cause for the problem. In some
cases, because of the design of the diagnostic test
procedure, a DTC can be the reason for another DTC
to be set. Therefore, it is important that the test pro-
cedures be followed in sequence, to understand what
caused a DTC to be set.
ERASING DIAGNOSTIC TROUBLE CODES
The DRB Scan Tool must be used to erase a DTC.
REMOVAL AND INSTALLATION
GENERATOR
REMOVAL
(1) Disconnect battery negative cable (Fig. 6).
(2) Loosen but DO NOT remove the generator
adjustment nut.
(3) Raise vehicle with front wheels turned fully to
the right.
(4) Remove the plastic lower splash shield.
(5) Disconnect the generator field circuit wiring
connector (Fig. 9). Squeeze locking tab to release.
(6) Remove the B+ terminal nut and wire.
(7) Loosen pivot bolt, but do not remove (Fig. 8)
and (Fig. 9).
(8) Remove the generator drive belt. The generator
spill shield does not need to be removed.
(9) Remove three mounting pivot bracket bolts.
(10) Remove pivot bolt and bracket.
(11) Holding the generator in one hand, remove
adjustment nut and slide the generator off the T-bolt.
The T-bolt does not need to be removed.
(12) Lower the generator and remove through the
wheel well.
INSTALLATION
(1) For installation, reverse above procedures. The
generator field connector has a locking tab and will
snap when fully installed. Refer to group 7 Cooling
System, Belt Removal/Install Adjust. Tighten all fas-
teners to the proper torque. Refer to the Torque Spec-
Fig. 5 Battery Temperature Sensor
Fig. 6 Removal/Installation of Battery Cables
8C - 10 CHARGING SYSTEMPL
DIAGNOSIS AND TESTING (Continued)

IGNITION SYSTEM
CONTENTS
page page
GENERAL INFORMATION
INTRODUCTION......................... 1
DESCRIPTION AND OPERATION
AUTOMATIC SHUTDOWN RELAY............ 3
CAMSHAFT POSITION SENSOR............. 4
COMBINATION ENGINE COOLANT
TEMPERATURE SENSOR................. 5
CRANKSHAFT POSITION SENSOR........... 4
ELECTRONIC IGNITION COILS.............. 3
IGNITION INTERLOCK.................... 7
IGNITION SWITCH....................... 7
IGNITION SYSTEM....................... 1
INTAKE AIR TEMPERATURE SENSOR........ 6
KNOCK SENSOR......................... 6
LOCK KEY CYLINDER..................... 7
MANIFOLD ABSOLUTE PRESSURE SENSOR
(MAP)............................... 6
POWERTRAIN CONTROL MODULE.......... 2
SPARK PLUG CABLES.................... 2
SPARK PLUGS.......................... 2
THROTTLE POSITION SENSOR (TPS)........ 6
DIAGNOSIS AND TESTING
CAMSHAFT POSITION SENSOR AND
CRANKSHAFT POSITION SENSOR......... 9
CHECK COIL TEST....................... 8
ENGINE COOLANT TEMPERATURE SENSOR . . . 9
FAILURE TO START TESTÐ2.0/2.4L......... 8
IGNITION TIMING PROCEDURE............. 9
INTAKE AIR TEMPERATURE SENSOR........ 9
MANIFOLD ABSOLUTE PRESSURE (MAP)
SENSOR TEST......................... 9
SPARK PLUG CONDITION................ 10TESTING FOR SPARK AT COILÐ2.0/2.4L..... 7
THROTTLE POSITION SENSOR............. 9
REMOVAL AND INSTALLATION
AUTOMATIC SHUTDOWN RELAY........... 13
CAMSHAFT POSITION SENSORÐDOHC..... 14
CAMSHAFT POSITION SENSORÐSOHC..... 13
COMBINATION ENGINE COOLANT
TEMPERATURE SENSORÐDOHC........ 15
COMBINATION ENGINE COOLANT
TEMPERATURE SENSORÐSOHC......... 15
CRANKSHAFT POSITION SENSOR.......... 15
IGNITION COIL......................... 13
IGNITION INTERLOCK................... 18
IGNITION SWITCH...................... 16
LOCK CYLINDER HOUSING............... 18
LOCK KEY CYLINDER.................... 17
MAP/IAT SENSORÐDOHC................ 16
MAP/IAT SENSORÐSOHC................ 16
POWERTRAIN CONTROL MODULE (PCM) . . . 12
SPARK PLUG CABLE SERVICE............ 13
SPARK PLUG SERVICE.................. 12
SPARK PLUG TUBES.................... 13
THROTTLE POSITION SENSOR............ 16
SPECIFICATIONS
FIRING ORDERÐ2.0L................... 18
IGNITION COIL......................... 19
SPARK PLUG CABLE RESISTANCEÐDOHC . . 18
SPARK PLUG CABLE RESISTANCEÐSOHC . . . 18
SPARK PLUG.......................... 19
TORQUE SPECIFICATION................. 18
VECI LABEL........................... 18
GENERAL INFORMATION
INTRODUCTION
This section describes the electronic ignition sys-
tem for the 2.0L engines used in Neon vehicles.
The On-Board Diagnostics Section in Group 25
describes diagnostic trouble codes.
Group 0, Lubrication and Maintenance, contains
general maintenance information for ignition relateditems. The Owner's Manual also contains mainte-
nance information.DESCRIPTION AND OPERATION
IGNITION SYSTEM
Ignition system operation and diagnostics, are
identical for 2.0L Single Overhead Cam (SOHC) and
2.0L Duel Overhead Cam (DOHC) engines.
PLIGNITION SYSTEM 8D - 1

The major difference between the two engines is
component location which affects the ignition system
service procedures. There are various sensors that
are in different locations due to a different cylinder
head and intake manifold.
The 2.0L engines use a fixed ignition timing sys-
tem. The distributorless electronic ignition system is
referred to as the Direct Ignition System (DIS).
Basic ignition timing is not adjustable.The
Powertrain Control Module (PCM) determines spark
advance. The system's three main components are
the coil pack, crankshaft position sensor, and cam-
shaft position sensor.
POWERTRAIN CONTROL MODULE
The Powertrain Control Module (PCM) controls the
ignition system (Fig. 1). The PCM supplies battery
voltage to the ignition coil through the Auto Shut-
down (ASD) Relay. The PCM also controls the ground
circuit for the ignition coil. By switching the ground
path for the coil on and off, the PCM adjusts ignition
timing to meet changing engine operating conditions.
During the crank-start period the PCM maintains
spark advance at 9É BTDC. During engine operation
the following inputs determine the amount of spark
advance provided by the PCM.
²Intake air temperature
²Coolant temperature
²Engine RPM
²Intake manifold vacuum
²Knock sensor
The PCM also regulates the fuel injection system.
Refer to the Fuel Injection sections of Group 14.
SPARK PLUGS
The 2.0L engines uses resistor spark plugs. For
spark plug identification and specifications, Refer to
the Specifications section at the end of this group.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 0.
Spark plugs that have low mileage may be cleaned
and reused if not otherwise defective. Refer to the
Spark Plug Condition section of this group. After
cleaning, file the center electrode flat with a small
point file or jewelers file. Adjust the gap between the
electrodes (Fig. 2) to the dimensions specified in the
chart at the end of this section.
Always tighten spark plugs to the specified torque.
Over tightening can cause distortion and damage.
Tighten spark plugs to 28 N´m (20 ft. lbs.) torque.
SPARK PLUG CABLES
Spark plug cables are sometimes referred to as sec-
ondary ignition wires. The wires transfer electrical
current from the coil pack to individual spark plugs
at each cylinder. The resistor type, nonmetallic spark
plug cables provide suppression of radio frequency
emissions from the ignition system.
Check the spark plug cable connections for good
contact at the coil and spark plugs. Terminals should
be fully seated. The nipples and spark plug covers
should be in good condition. Nipples should fit tightly
on the coil. Spark plug boot should completely cover
the spark plug hole in the cylinder head cover. Install
the boot until the terminal snaps over the spark
plug. A snap must be felt to ensure the spark plug
cable terminal engaged the spark plug.
Loose cable connections will corrode, increase resis-
tance and permit water to enter the coil towers.
These conditions can cause ignition malfunction.
Fig. 1 Powertrain Control Module
Fig. 2 Setting Spark Plug Electrode Gap
8D - 2 IGNITION SYSTEMPL
DESCRIPTION AND OPERATION (Continued)

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 0.38 volts to 1.2 volts at mini-
mum throttle opening (idle) to a maximum of 3.1
volts to 4.4 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.
IGNITION SWITCH
In the RUN position, the ignition switch connects
power from the Power Distribution Center (PDC) to a
30 amp fuse in the fuse block, back to a bus bar in
the PDC. The bus bar feeds circuits for the Power-
train Control Module (PCM), duty cycle purge sole-
noid, EGR solenoid, and ABS system. The bus bar in
the PDC feeds the coil side of the radiator fan relay,
A/C compressor clutch relay, and the fuel pump relay.
It also feeds the Airbag Control Module (ACM)
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. 16):
²Accessory
²Off (lock)
²Unlock
²On/Run
²Start
IGNITION INTERLOCK
All vehicles equipped with automatic transaxles
have an interlock system. The system prevents shift-
ing the vehicle out of Park unless the ignition lock
cylinder is in the Off, Run or Start position. In addi-
tion, the operator cannot rotate the key to the lock
position unless the shifter is in the park position. On
vehicles equipped with floor shift refer to Group 21 -
Transaxle for Automatic Transmission Shifter/Igni-
tion Interlock.
DIAGNOSIS AND TESTING
TESTING FOR SPARK AT COILÐ2.0/2.4L
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.
NOTE: New isolated engine valve cover may not
provide adequate ground. Use engine block as
engine ground.
Fig. 15 MAP/IAT sensorÐDOHCFig. 16 Ignition Lock Cylinder Detents
PLIGNITION SYSTEM 8D - 7
DESCRIPTION AND OPERATION (Continued)

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. 17).
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.
CHECK COIL TEST
NOTE: 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 the ignition cables and measure the
resistance of the cables. Resistance must be between
ranges shown in chart in specifcation section in this
group. 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. 18). Resistance on the primary side of eachcoil should be 0.45 - 0.65 ohm. 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. 19). Secondary resistance should be 11,000 to
14,000 ohms. Replace the coil if resistance is not
within tolerance.
FAILURE TO START TESTÐ2.0/2.4L
This no-start test checks the camshaft position sen-
sor and crankshaft position sensor.
Use the DRB scan tool to test the camshaft posi-
tion sensor and the sensor circuits. Refer to the
appropriate Powertrain Diagnostics Procedure Man-
ual. Refer to the wiring diagrams section for circuit
information.
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-
Fig. 17 Testing For Spark
Fig. 18 Terminal Identification
Fig. 19 Checking Ignition Coil Secondary
Resistance
8D - 8 IGNITION SYSTEMPL
DIAGNOSIS AND TESTING (Continued)

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 approxi-
mately 12.66 volts or higher to perform failure to
start test.
(2) Disconnect the harness connector from the coil
pack (Fig. 20).
(3) Connect a test light to the B+ (battery voltage)
terminal of the coil electrical connector and ground.
The B+ wire for the DIS coil is the center terminal.
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 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.
(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
either the crankshaft position sensor/camshaft posi-
tion sensor 8 volt supply circuit, or the camshaft
position sensor output or ground circuits.
IGNITION TIMING PROCEDURE
The engines for this vehicle, use a fixed ignition
system. The PCM regulates ignition timing. Basic
ignition timing is not adjustable.
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.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
TEST
Refer to Group 14, Fuel System for Diagnosis and
Testing.
THROTTLE POSITION SENSOR
To perform a complete test of the this sensor and
its circuitry, refer to the DRB scan tool and appropri-
ate Powertrain Diagnostics Procedures manual. To
test the throttle position sensor only, refer to the fol-
lowing:
The Throttle Position Sensor (TPS) can be tested
with a digital voltmeter (DVM). The center terminal
of the sensor is the output terminal. One of the other
terminals is a 5 volt supply and the remaining ter-
minal is ground.
Fig. 20 Ignition Coil Engine Harness Connector
PLIGNITION SYSTEM 8D - 9
DIAGNOSIS AND TESTING (Continued)

Connect the DVM between the center and sensor
ground terminal. Refer to Group 8W - Wiring Dia-
grams for correct pinout.
With the ignition switch in the ON position, check
the output voltage at the center terminal wire of the
connector. Check the output voltage at idle and at
Wide-Open-Throttle (WOT). At idle, TPS output volt-
age should be approximately 0.38 volts to 1.2 volts.
At wide open throttle, TPS output voltage should be
approximately 3.1 volts to 4.4 volts. The output volt-
age should gradually increase as the throttle plate
moves slowly from idle to WOT.
Check for spread terminals at the sensor and PCM
connections before replacing the TPS.
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. 21). 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 rust
colored 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. 21). 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. 22). Sometimes fuel additives
can cause ash encrustation on an entire set of spark
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.
Fig. 21 Normal Operation and Cold (Carbon) Fouling
8D - 10 IGNITION SYSTEMPL
DIAGNOSIS AND TESTING (Continued)