Camshaft ISUZU TF SERIES 2004 Repair Manual

3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-3
DTC P0201 (FLASH CODE 31) INJECTOR 1
CONTROL CIRCUIT ........................................ 6E-226
DTC P0202 (FLASH CODE 31) INJECTOR 2
CONTROL CIRCUIT ........................................ 6E-226
DTC P0203 (FLASH CODE 31) INJECTOR 3
CONTROL CIRCUIT ........................................ 6E-226
DTC P0204 (FLASH CODE 31) INJECTOR 4
CONTROL CIRCUIT ........................................ 6E-226
DTC P0205 (FLASH CODE 31) INJECTOR 5
CONTROL CIRCUIT ........................................ 6E-226
DTC P0206 (FLASH CODE 31) INJECTOR 6
CONTROL CIRCUIT ........................................ 6E-226
DTC P0336 (FLASH CODE 29) CRANKSHAFT
POSITION SENSOR CIRCUIT
RANGE/PERFORMANCE (58X) ...................... 6E-234
DTC P0337 (FLASH CODE 29) CRANKSHAFT
POSITION SENSOR CIRCUIT NO SIGNAL
(58X) ................................................................. 6E-234
DTC P0341 (FLASH CODE 41) CAMSHAFT
POSITION SENSOR CIRCUIT
RANGE/PERFORMANCE ............................... 6E-243
DTC P0342 (FLASH CODE 41) CAMSHAFT
POSITION SENSOR CIRCUIT NO SIGNAL .... 6E-243
DTC P0351 (FLASH CODE 42) IGNITION 1
CONTROL CIRCUIT ........................................ 6E-249
DTC P0352 (FLASH CODE 42) IGNITION 2
CONTROL CIRCUIT ........................................ 6E-249
DTC P0353 (FLASH CODE 42) IGNITION 3
CONTROL CIRCUIT ........................................ 6E-249
DTC P0354 (FLASH CODE 42) IGNITION 4
CONTROL CIRCUIT ........................................ 6E-249
DTC P0355 (FLASH CODE 42) IGNITION 5
CONTROL CIRCUIT ........................................ 6E-249
DTC P0356 (FLASH CODE 42) IGNITION 6
CONTROL CIRCUIT ........................................ 6E-249
DTC P0404 (FLASH CODE 32) EGR CIRCUIT
RANGE/PERFORMANCE (OPEN VALVE)....... 6E-258
DTC P1404 (FLASH CODE 32) EGR CIRCUIT
RANGE/PERFORMANCE (CLOSED VALVE) .. 6E-258
DTC P0405 (FLASH CODE 32) EGR
CIRCUIT LOW.................................................. 6E-263
DTC P0406 (FLASH CODE 32) EGR
CIRCUIT HIGH ................................................. 6E-268
DTC P0444 EVAP PURGE SOLENOID
VALVE CIRCUIT LOW VOLTAGE ................... 6E-274
DTC P0445 EVAP PURGE SOLENOID
VALVE CIRCUIT HIGH VOLTAGE .................. 6E-274
DTC P0500 (FLASH CODE 24) VEHICLE
SPEED SENSOR (VSS) CIRCUIT
RANGE/PERFORMANCE ................................ 6E-279 DTC P0562 (FLASH CODE 66) SYSTEM
VOLTAGE LOW .............................................. 6E-288
DTC P0563 (FLASH CODE 66) SYSTEM
VOLTAGE HIGH .............................................. 6E-321
DTC P0601 (FLASH CODE 51) ENGINE
CONTROL MODULE (ECM) MEMORY
CHECKSUM ..................................................... 6E-293
DTC P0602 PROGRAMMING ERROR............. 6E-295
DTC P1508 (FLASH CODE 22) IDLE AIR
CONTROL SYSTEM LOW/CLOSED ............... 6E-296
DTC P1509 (FLASH CODE 22) IDLE AIR
CONTROL SYSTEM HIGH/OPEN ................... 6E-296
DTC P1601 (FLASH CODE 65) CAN BUS
OFF .................................................................. 6E-304
DTC U2104 (FLASH CODE 67) CAN BUS
RESET COUNTER OVER-RUN ...................... 6E-310
DTC P1626 IMMOBILIZER NO SIGNAL ........... 6E-317
DTC P1631 IMMOBILIZER WRONG
SIGNAL ............................................................ 6E-323
DTC P1648 IMMOBILIZER WRONG
SECURITY CODE ENTERED .......................... 6E-325
DTC P1649 IMMOBILIZER FUNCTION NOT
PROGRAMMED ................................................ 6E-327
SYMPTOM DIAGNOSIS ................................... 6E-329
PRELIMINARY CHECKS .............................. 6E-329
VISUAL/PHYSICAL CHECK .......................... 6E-329
INTERMITTENT ............................................. 6E-329
ENGINE CRANKS BUT WILL NOT RUN ......... 6E-331
HARD START SYMPTOM ................................ 6E-334
ROUGH, UNSTABLE, OR INCORRECT
IDLE, STALLING SYMPTOM ........................... 6E-337
SURGES AND/OR CHUGS SYMPTOM ........... 6E-341
HESITATION, SAG, STUMBLE SYMPTOM ..... 6E-345
CUTS OUT, MISSES SYMPTOM ..................... 6E-347
LACK OF POWER, SLUGGISH OR SPONGY
SYMPTOM ....................................................... 6E-352
DETONATION/SPARK KNOCK SYMPTOM..... 6E-356
POOR FUEL ECONOMY SYMPTOM ............... 6E-359
EXCESSIVE EXHAUST EMISSIONS OR
ODORS SYMPTOM ......................................... 6E-362
DIESELING, RUN-ON SYMPTOM .................... 6E-365
BACKFIRE SYMPTOM ..................................... 6E-366
ON-VEHICLE SERVICE PROCEDURE ........... 6E-368
ENGINE CONTROL MODULE (ECM) .............. 6E-368
CRANKSHAFT POSITION (CKP) SENSOR ..... 6E-369
CAMSHAFT POSITION (CMP) SENSOR ......... 6E-369
ENGINE COOLANT TEMPERATURE (ECT)
SENSOR .......................................................... 6E-370
MASS AIR FLOW (MAF) SENSOR & INTAKE AIR
TEMPERATURE (IAT) SENSOR ...................... 6E-370

3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-5
ABBREVIATION CHARTS

Abbreviations Appellation
A/C Air conditioner
A/T Automatic transmission
ACC Accessory
BLK Black
BLU Blue
BRN Brown
CAN Controller Area Network
CEL Check engine lamp
CKP Crankshaft position
CMP Camshaft position
DLC Data link connector
DTC Diagnosis trouble code
DVM Digital voltage meter
ECM Engine control module
ECT Engine coolant temperature
EEPROM Electrically erasable & programmable read only memory
EGR Exhaust gas recalculation
GND Ground
GRY Gray
HO2S Heated Oxygen Sensor
IAT Intake air temperature
IAC Idle air control
IG Ignition
M/T Manual transmission
MAF Mass air flow
MIL Malfunction indicator lamp
OBD On-board diagnostic
ORN Orange
PNK Pink
PROM Programmable read only memory
RED Red
SW Switch
TPS Throttle position sensor
TCM Transmission control module
VCC Voltage Constant Control
VIO Violet
VSS Vehicle speed sensor
WHT White
WOT Wide open throttle
YEL Yellow

6E-8 3.5L ENGINE DRIVEABILITY AND EMISSIONS





(1) Bank 1 Heated Oxygen Sensor (RH)



(1) Bank 2 Heated Oxygen Sensor (LH)





1
(1) Crankshaft Position (CKP) Sensor



(1) Camshaft Position Sensor (CMS)
(2) EGR Valve





(1) Canister



(1) Fuel Tank
(2) Fuel Pump

3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-47
Signal or Continuity Tester Position Pin
No. B/Box
No. Pin Function Wire
Color
Key SW Off Key SW On Engine IdleEngine
2000rpm ECM
Connection Range (+) (-)
B16 B16 Idle Air Control
(IAC) Valve
Coil A Low BLU/
RED Less than 1V Less than 1V / 10-14V Connect DC V B16 GND
B17 B17 Idle Air Control
(IAC) Valve
Coil B Low BLU/
BLKLess than 1V Less than 1V / 10-14V Connect DC V B17 GND
B18 B18 Check Engine
Lamp
(Immobilizer
Control Unit
Terminal B7) BRN/
YELLess than 1V Less than 1VLamp is turned on:
Less than 1V
Lamp is turned off: 10-14VConnect DC V B18 GND
B19 B19 Fuel Pump
Relay GRN/
WHT Less than 1V While relay is
activated:
10-14V
Relay is not
activated:
Less than 1V10-14V Connect DC V B19 GND
B20 B20 Mass Air Flow
(MAF) Sensor BLK/
YELLess than 1V Approx. 0.47VApprox. 1.5V
at 750 rpmApprox. 2V Connect DC V B20 GND
B21 B21 Bank 1 Oxygen
Sensor Signal PNK Less than 1V Approx. 0.4V 0.1 - 0.9V Connect DC V B21 B22
B22 B22 Bank 1 Oxygen
Sensor Ground BLU/
YELContinuity
with ground - - - Connect Ohm B22 GND
B23 B23 Bank 2 Oxygen
Sensor Signal RED Less than 1V Approx. 0.4V 0.1 - 0.9V Connect DC V B23 B24
B24 B24 Bank 2 Oxygen
Sensor Ground BLU/
BLKContinuity
with ground - - - Connect Ohm B24 GND
B25 B25 To Data Link
Connector
No.6 BLK/
GRN - - - - - - - -
B26 B26 Throttle
Position
Sensor (TPS)
Signal BLU Less than 1V Approx. 0.5V Approx. 0.6V Connect DC V B26 B39
B27 B27 TPS & Cam
Position
Sensor +5V
Supply GRN Less than 1V Approx. 5V Connect DC V B27 B39
B28 B28 Camshaft
Position (CMP)
Sensor Signal BLU - - Wave form - - - -
B29 B29 Inhibitor Switch
(AT Only) BLK Less than 1V P or N range: Less than 1V
Other than P or N range: 10-14V Connect DC V B29 GND
B30 B30 Power Steering
Pressure
Switch GRN/
YELLess than 1V Pressure switch is turned on: Less than 1V
Pressure Switch is turned off: 10-14V Connect DC V B30 GND
B31 B31 A/C Thermo
Relay GRN/
BLKLess than 1V A/C request is activated: 10-14V
A/C request is not activated: Less than 1VConnect DC V B31 GND

3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-49
Camshaft Position (CMP) Sensor Reference Wave Form









0V








Measurement Terminal: B28(+) B39(-)
Measurement Scale: 5V/div 10ms/div
Measurement Condition: Approximately 2000rpm
Crankshaft Position (CKP) Sensor Reference Wave Form









0V








Measurement Terminal: A23(+) A25(-)
Measurement Scale: 2.0V/div 5ms/div
Measurement Condition: Approximately 2000rpm
Crankshaft Position (CKP) Sensor & Camshaft Position (CMP)
Sensor Reference Wave Form







CH1
0V



CH2
0V




Measurement Terminal: CH1: A23(+) / CH2: B28(+) GND(-)
Measurement Scale: 2V/div / CH2: 5V/div 10ms/div
Measurement Condition: Approximately 2000rpm
Crankshaft Position (CKP) Sensor & Tacho Output Signal
Reference Wave Form







CH1
0V



CH2
0V




Measurement Terminal: CH1: A23(+) / CH2: B12(+) GND(-)
Measurement Scale: CH1: 2V/div / CH2: 10V/div 5ms/div
Measurement Condition: Approximately 2000rpm
Vehicle Speed Sensor (VSS) Reference Wave Form








CH1
0V


CH2
0V




Measurement Terminal: CH1: ECM B32(+) / CH2: VSS 3(+)
GND(-)
Measurement Scale: CH1: 10V/div / CH2: 10V/div 50ms/div
Measurement Condition: Approximately 20km/h
Note: The vehicle is without immobilizer system,
CH1 signal is same as CH2.
Heated Oxygen Sensor (HO2S) Reference Wave Form





CH1
0V





CH2
0V





Measurement Terminal: CH1: B21(+) / CH2: B23(+) GND(-)
Measurement Scale: CH1: 500mV/div / CH2: 500mV/div 1s/div
Measurement Condition: Approximately 2000rpm in Closed Loop

3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-51

GENERAL DESCRIPTION FOR ECM AND
SENSORS
Engine Control Module (ECM)


1 2
(1) A Port
(2) B Port


The engine control module (ECM) is located on the
common chamber. The ECM controls the following.

Fuel metering system

Ignition timing

On-board diagnostics for powertrain functions.

The ECM constantly observes the information from
various sensors. The ECM controls the systems tha
t
affect vehicle performance. And it performs the
diagnostic function of the system.
The function can recognize operational problems, and
warn to the driver through the check engine lamp, and
store diagnostic trouble code (DTC). DTCs identify the
problem areas to aid the technician in marking repairs.

The input / output devices in the ECM include analog to
digital converts, signal buffers, counters and drivers.
The ECM controls most components with electronic
switches which complete a ground circuit when turned
on.

Inputs (Operating condition read):

Battery voltage

Electrical ignition

Exhaust oxygen content

Mass air flow

Intake air temperature

Engine coolant temperature

Crankshaft position

Camshaft position

Throttle position

Vehicle speed

Power steering pressure

Air conditioning request on or off

EGR valve position

Outputs (Systems controlled):

Ignition control

Fuel control

Idle air control

Fuel pump

EVAP canister purge

Air conditioning

Diagnostics functions

The vehicle with automatic transmission, the
interchange of data between the engine control module
(ECM) and the transmission control module (TCM) is
performed via a CAN-bus system.
The following signals are exchanged via the CAN-bus:

ECM to TCM:

ECM CAN signal status

Engine torque

Coolant temperature

Throttle position

Engine speed

A/C status

CAN valid counter

TCM to ECM:

Ignition timing retard request

Garage shift status

CAN valid counter

3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-53
Idle Air Control (IAC) Valve








Step
CoilAB CD
Coil A High
(EC M B13)On On
Coil A Low
(EC M B16)On On
Coil B High
(EC M B14)On On
Coil B Low
(EC M B17)On On

(IAC Valve Close Direction)
(IAC Valve Open Direction)



The idle air control valve (IAC) valve is two directional
and gives 2-way control. It has a stepping moto
r
capable of 256 steps, and also has 2 coils. With power
supply to the coils controlled steps by the engine control
module (ECM), the IAC valve's pintle is moved to adjus
t
idle speed, raising it for fast idle when cold or there is
extra load from the air conditioning or power steering.
By moving the pintle in (to decrease air flow) or out (to
increase air flow), a controlled amount of the air can
move around the throttle plate. If the engine speed is
too low, the engine control module (ECM) will retract the
IAC pintle, resulting in more air moving past the throttle
plate to increase the engine speed.
If the engine speed is too high, the engine control
module (ECM) will extend the IAC pintle, allowing less
air to move past the throttle plate, decreasing the
engine speed.

The IAC pintle valve moves in small step called counts.
During idle, the proper position of the IAC pintle is
calculated by the engine control module (ECM) based
on battery voltage, coolant temperature, engine load,
and engine speed.
If the engine speed drops below a specified value, and
the throttle plate is closed, the engine control module
(ECM) senses a near-stall condition. The engine control
module (ECM) will then calculate a new IAC pintle valve
position to prevent stalls. If the IAC valve is disconnected and reconnected with
the engine running, the idle speed will be wrong. In this
case, the IAC must be reset. The IAC resets when the
key is cycled "On" then "Off". When servicing the IAC, i
t
should only be disconnected or connected with the
ignition "Off".
The position of the IAC pintle valve affects engine start-
up and the idle characteristic of the vehicle.
If the IAC pintle is fully open, too much air will be
allowed into the manifold. This results in high idle
speed, along with possible hard starting and lean
air/fuel ratio.

Camshaft Position (CMP) Sensor








12
(1) Camshaft Position (CMP) Sensor
(2) EGR Valve


With the use of sequential multi-point fuel injection, a
hall element type camshaft position (CMP) is adopted to
provide information to be used in making decisions on
injection timing to each cylinder. It is mounted on the
rear of the left-hand cylinder head and sends signals to
the ECM.
One pulse is generated per two rotations of crankshaft.

6E-54 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Crankshaft Position (CKP) Sensor





The crankshaft position (CKP) sensor, which sends a
signal necessary for deciding on injection timing to the
ECM, is mounted on the right-hand side of the cylinde
r
block.
The crankshaft has a 58 teeth press-fit timing disc, from
which the CKP sensor reads the position of the
crankshaft at all the times. It converts this to an
electrical signal, which it sends to the ECM.
Of the 58 teeth, 57 have a base with of 3°, and are
evenly spaced, but tooth No. 58 is 15° wide at its based
to serve as a timing mark, allowing the sensor to repor
t
the standard crankshaft position.
Using the 58 X signals per rotation and the timing-mark
signal sent by the CKP sensor, the ECM is able to
accurately calculate engine speed and crank position.
Also, the position of each cylinder is precisely known by
the ECM from signals sent by the camshaft position
(CMP) sensor, so the sequential multi-point fuel
injection can be controlled with accuracy.

The 58 X signals are converted by the ECM into a
retangle wave signal. This converted signal is sent from
the ECM terminal B12 to the tachometer and transfe
r
case control module (TCCM) terminal 15 (if 4WD
model).
Engine Coolant Temperature (ECT) Sensor




















The ECT sensor is a thermistor. A temperature
changes the resistance value. And it changes voltage.
In other words it measures a temperature value. It is
installed on the coolant stream. Low coolan
t
temperature produces a high resistance.
The ECM supplies 5 volts signal to the ECT senso
r
through resisters in the ECM and measures the voltage.
The signal voltage will be high when the engine
temperature is cold, and it will be low when the engine
temperature is hot.

Characteris tic of ECT Sens or
10 100 1000 10000 100000-3010 50 90130Temperature (

)
Resistance (Ω)

3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-57
Starting Mode
When the ignition is first turned "ON," the ECM
energizes the fuel pump relay for two seconds to allo
w
the fuel pump to build up pressure. The ECM then
checks the engine coolant temperature (ECT) senso
r
and the throttle position sensor to determine the proper
air/fuel ratio for starting.
The ECM controls the amount of fuel delivered in the
starting mode by adjusting how long the fuel injectors
are energized by pulsing the injectors for very short
times.

Fuel Metering System Components
The fuel metering system is made up of the following
parts.

Fuel injector

Throttle Body

Fuel Rail

Fuel Pressure regulator

ECM

Crankshaft position (CKP) sensor

Camshaft position (CMP) sensor

Idle air control valve

Fuel pump

Fuel Injector
The sequential multi-port fuel injection fuel injector is a
solenoid operated device controlled by the ECM. The
ECM energizes the solenoid, which opens a valve to
allow fuel delivery.
The fuel is injected under pressure in a conical spray
pattern at the opening of the intake valve. Excess fuel
not used by the injectors passes through the fuel
pressure regulator before being returned to the fuel
tank.

Fuel Pressure Regulator
The fuel pressure regulator is a diaphragm-operated
relief valve mounted on the fuel rail with fuel pump
pressure on one side and manifold pressure on the
other side. The fuel pressure regulator maintains the
fuel pressure available to the injector at three times
barometric pressure adjusted for engine load. It may be
serviced separate.
If the pressure is too low, poor performance and a DTC
P0131, P0151, P0171, P0174, P1171 or P1174 will be
the result. If the pressure is too high, excessive odo
r
and/or a DTC P0132, P0152, P0172 or P0175 will be
the result. Refer to Fuel System Diagnosisfo
r
information on diagnosing fuel pressure conditions.
Fuel Rail
The fuel rail is mounted to the top of the engine and
distributes fuel to the individual injectors. Fuel is
delivered to the fuel inlet tube of the fuel rail by the fuel
lines. The fuel goes through the fuel rail to the fuel
pressure regulator. The fuel pressure regulato
r
maintains a constant fuel pressure at the injectors.
Remaining fuel is then returned to the fuel tank.







055RV009
Fuel Pump Electrical Circuit
When the key is first turned "ON," the ECM energizes
the fuel pump relay for two seconds to build up the fuel
pressure quickly. If the engine is not started within two
seconds, the ECM shuts the fuel pump off and waits
until the engine is cranked. When the engine is cranked
and the 58 X crankshaft position signal has been
detected by the ECM, the ECM supplies 12 volts to the
fuel pump relay to energize the electric in-tank fuel
pump.
An inoperative fuel pump will cause a "no-start"
condition. A fuel pump which does not provide enough
pressure will result in poor performance.

Camshaft Position (CMP) Sensor Signal
The ECM uses this signal to determine the position o
f
the number 1 piston during its power stroke, allowing
the ECM to calculate true sequential multiport fuel
injection. Loss of this signal will set a DTC P0341. If the
CMP signal is lost while the engine is running, the fuel
injection system will shift to a calculated sequential fuel
injection based on the last fuel injection pulse, and the
engine will continue to run. The engine can be restarted
and will run in the calculated sequential mode as long
as the fault is present, with a 1-in-6 chance of being
correct.

6E-58 3.5L ENGINE DRIVEABILITY AND EMISSIONS
GENERAL DESCRIPTION FOR
ELECTRONIC IGNITION SYSTEM IGNITION
COILS & CONTROL
A separate coil-at-plug module is located at each spark
plug.
The coil-at-plug module is attached to the engine with
two screws. It is installed directly to the spark plug by an
electrical contact inside a rubber boot.
A three way connector provides 12 volts primary supply
from the ignition coil fuse, a ground switching trigge
r
line from the ECM, and ground.
The ignition control spark timing is the ECM's method o
f
controlling the spark advance and the ignition dwell.
The ignition control spark advance and the ignition dwell
are calculated by the ECM using the following inputs.

Engine speed

Crankshaft position (CKP) sensor

Camshaft position (CMP) sensor

Engine coolant temperature (ECT) sensor

Throttle position sensor

Park or neutral position switch

Vehicle speed sensor

ECM and ignition system supply voltage

Based on these sensor signal and engine load
information, the ECM sends 5V to each ignition coil
requiring ignition. This signal sets in the powe
r
transistor of the ignition coil to establish a grounding
circuit for the primary coil, applying battery voltage to
the primary coil.
At the ignition timing, the ECM stops sending the 5V
signal voltage. Under this condition the power transistor
of the ignition coil is set off to cut the battery voltage to
the primary coil, thereby causing a magnetic field
generated in the primary coil to collapse.
On this moment a line of magnetic force flows to the
secondary coil, and when this magnetic line crosses the
coil, high voltage induced by the secondary ignition
circuit to flow through the spark plug to the ground.

Ignition Control ECM Output
The ECM provides a zero volt (actually about 100 mV to
200 mV) or a 5-volt output signal to the ignition control
(IC) module. Each spark plug has its own primary and
secondary coil module ("coil-at-plug") located at the
spark plug itself. When the ignition coil receives the
5-volt signal from the ECM, it provides a ground path fo
r
the B+ supply to the primary side of the coil-at -plug
module. This energizes the primary coil and creates a
magnetic field in the coil-at-plug module. When the
ECM shuts off the 5-volt signal to the ignition control
module, the ground path for the primary coil is broken.
The magnetic field collapses and induces a high voltage
secondary impulse which fires the spark plug and
ignites the air/fuel mixture.
The circuit between the ECM and the ignition coil is
monitored for open circuits, shorts to voltage, and
shorts to ground. If the ECM detects one of these
events, it will set one of the following DTCs:

P0351: Ignition coil Fault on Cylinder #1

P0352: Ignition coil Fault on Cylinder #2

P0353: Ignition coil Fault on Cylinder #3

P0354: Ignition coil Fault on Cylinder #4

P0355: Ignition coil Fault on Cylinder #5

P0356: Ignition coil Fault on Cylinder #6

Spark Plug
Although worn or dirty spark plugs may give satisfactory
operation at idling speed, they frequency fail at highe
r
engine speeds. Faulty spark plugs may cause poor fuel
economy, power loss, loss of speed, hard starting and
generally poor engine performance. Follow the
scheduled maintenance service recommendations to
ensure satisfactory spark plug performance. Refer to
Maintenance and Lubrication.
Normal spark plug operation will result in brown to
grayish-tan deposits appearing on the insulator portion
of the spark plug. A small amount of red-brown, yellow,
and white powdery material may also be present on the
insulator tip around the center electrode. These
deposits are normal combustion by-products of fuels
and lubricating oils with additives. Some electrode wea
r
will also occur. Engines which are not running properly
are often referred to as “misfiring." This means the
ignition spark is not igniting the air/fuel mixture at the
proper time.
Spark plugs may also misfire due to fouling, excessive
gap, or a cracked or broken insulator. If misfiring
occurs before the recommended replacement interval,
locate and correct the cause.