turn signal ISUZU TROOPER 1995 User Guide

FUEL SYSTEM
• CHECK:
• CHECK:
• CHECK:
• CHECK:
• CHECK:
• CHECK:
Fuel pump relay operation-pump should
turn "ON" for 2 seconds when ignition is
turned
"ON". Use CHART A-5.
Fuel injectors are correct for the vehicle.
Fuel
pressure, use CHART A-7.
Contaminated
fuel.
Engine fuse (visual inspect).
A
faulty in-tank fuel pump check valve will
allow
the fuel in the lines to drain back to
the tank after engine is stopped. To check
for this condition, perform fuel system
diagnosis CHART A-7.
IGNITION SYSTEM
• CHECK: For proper ignition voltage output with
spark tester J26792 or equivalent (ST-
125).
DRIVEABILITY AND EMISSIONS 6E2-91
• CHECK: Spark plugs. Remove spark plugs, check
for wet plugs, cracks, wear, improper
gap, burned electrodes, or heavy
deposits. Repair
or replace as necessary.
• CHECK: Bare or shorted wires.
• CHECK: Loose ignition coil ground.
ADDITIONAL CHECKS
• CHECK: Idle air control operation-use CHART C-
2C.
• CHECK: Basic engine problem. Refer to ENGINE
MECHANICAL DIAGNOSIS (SECTION
6A).
• CHECK: Service Bulletins for calibration updates.
SURGES AND/OR CHUGGLES
Definition: Engine power variation under steady
throttle or cruise. Feels like the car speeds
up and
slows down with no change in the
acceleration pedal.
PRELIMINARY CHECKS
• Perform the careful visual checks as described at
start
of "Symptoms," Section "6E2-B."
•
Be sure driver understands transmission
operation, and air conditioning compressor
operation
as explained in the owner's manual.
SENSORS
• CHECK: Heated oxygen sensor (H02S). The
H02S should respond quickly to different
throttle position, if it does not, check the
H02S for silicon or other contaminations
from fuel, or use of improper RTV sealant.
The sensor may have a white, powdery
coating and result in a high but false
signal voltage
(rich heated H02S signal
indication). The engine control module
will
then reduce the amount of fuel
delivered
to the engine, causing a severe
driveability problem. Also, watch for
green glycol contamination or cracking.
FUEL SYSTEM
• NOTICE: To determine ifthe condition is caused by
a rich
or lean system, the car should be
driven at the speed of the complaint.
Monitoring block learn will help identify a
problem.
Lean -Block learn above 142. Refer to
"Diagnostic Aids" on facing page of
diagnostic trouble code 44.
Rich -L.T. Fuel Trim above 118. Refer to
"Diagnostic Aids" on facing page of
diagnostic trouble code 45.
• CHECK: Fuel pressure while condition exists. Use
CHART A-7.
• CHECK: In-line fuel filter. Replace if dirty or
plugged.
IGNITION SYSTEM
• CHECK: For proper ignition voltage output using
spark tester (ST-125) J26792
or
equivalent .
• CHECK: Spark plugs. Remove spark plugs, check
for wet plugs, cracks, wear, improper
gap, burned electrodes, or heavy
deposits. Repair
or replace as necessary.
Also, check condition of electronic
ignition and spark plug wires.
• CHECK: Ignition timing. Using "Scan tool".
ADDITIONAL CHECKS
• CHECK: Engine control module grounds for being
clean, tight and in their proper location.
• CHECK: Vacuum lines for kinks or leaks.
• CHECK: Exhaust gas recirculation -There should
be no exhaust gas recirculation at idle.
Refer to CHART C-7.
• CHECK: Generator output voltage. Repair if less
than 9 or more than 16 volts.

6E2-1 02 DRIVEABILITV AND EMISSIONS
Throttle Position (TP) Sensor (Fig. 6E2-53)
The Throttle Position (TP) Sensor is a potentiometer
connected to the throttle shaft on the Throttle Body
(TB). The TP sensor electrical circuit consists of a 5
volts supply line (signal line) and a ground line,
provided by the Engine Control Module (ECM).
By
monitoring the voltage on the signal line the ECM
calculates throttle position. As the TB angle is changed
(accelerator pedal moved), the output
of TP sensor
also changes.
At a closed throttle position, the output
of the TP sensor is low (approximately 5volt). As the TB
opens, the output increases so that, at wide-open
throttle, the output voltage
will be between 4 and 5
volts.
The
ECM can determine fuel delivery based on TB
angle (driver demand). A broken or loose TP sensor
can cause intermittent bursts of fuel from the injector,
and
an unstable idle, because the ECM thinks the
throttle is moving. A problem in any
of the TP sensor
circuits should set a diagnostic trouble code
(DTC) 21.
Once a DTC is set, the ECM will use an artificial default
valueforTP sensor. A high idle will result when DTC 21
is set.
See
"On-Vehicle Service" for replacement or
adjustment
of TP sensor.
ECM
~--2. Throttle position
sensor (TPS)
Fig. 6E2-53
Manifold Absolute Pressure (MAP) Sensor (Fig.
6E2-54)
The Manifold Absolute Pressure (MAP) sensor
measures the changes in the intake manifold pressure
which result
from engine load and speed changes, and
converts this to a voltage output.
A closed throttle on engine coast
down would produce
a relatively
low MAP output, while a Wide Open
Throttle would produce a high output. MAP is the
OPPOSITE of what would be measured on a vacuum
gage. When manifold pressure is high, vacuum is low.
The
MAP sensor is also used to measure barometric
pressure under contain conditions, which
allows the
ECM to automatically adjust for different altitudes. The
ECM sends a 5 volts reference signal to the MAP
sensor. As the manifold pressure changes, the
electrical resistance
of the sensor also changes. By
monitoring the sensor output voltage, the ECM knows
the manifold pressure.
A higher pressure,
low vacuum (high voltage) requires
more fuel, while a lower pressure, higher vacuum (low
voltage) requires less
fuel.
A failure in the MAP sensor circuit should set a DTC 33.
Map sensor
Fig. 6E2-54
Vehicle Speed Sensor (VSS)
The Vehicle Speed Sensor, sends a pulsing voltage
signal to the
ECM, which the ECM converts to miles per
hour. This sensor helps to control the
operation
of the idle air control system.
See
ELECTRICAL DIAGNOSIS (SECTION 8A) for more
information.
Knock Sensor (KS) (DOHC only)
The Knock Sensor is mounted in the engine block.
When abnormal engine vibrations (spark knock) are
present, the sensor produces a voltage signal, which is
sent to the knock sensor module.
See
"Knock Sensor System," Section "6E2-C5" for
further information on the knock sensor system.
Air Conditioning (A/C) Request Signal
This signal tells the ECM that the Air Conditioning (A/C)
selector switch is turned
"ON". The ECM uses this to
adjust the idle speed, before turning
"ON" the A/C
clutch.
If this signal is not available to the ECM, the A/C
compressor will be inoperative.
See "A/C Compressor Clutch Control System", Section
"6E2-C1 0" for A/C wiring diagrams and diagnosis of
A/C electrical system.
Power Steering Pressure (PSP) Switch
This switch tells the ECM that the vehicle is in a parking
maneuver. The
ECM uses this information to
compensate
for the additional engine load by moving
the idle air control valve. The
ECM will also turn "OFF"
the A/C clutch when high pressure is detected.
•

6E2-1 04 DRIVEABILITV AND EMISSIONS
Engine Coolant Temperature (ECT) Sensor
A "Scan tool" displays engine temperature in degrees
centigrade. After engine is started, the temperature
should rise steadily to about 90°C then stabilize when
thermostat opens. If the engine has not been run for
several hours (overnight), the engine coolant
temperature (ECT) and intake air temperature (IAT)
readings should be close to each other. A fault in the
ECT sensor circuit should set a diagnostic trouble code
(DTC) 14. The DTC charts also contain a chart to check
for sensor resistance values relative to temperature.
Intake Air Temperature (IAT) Sensor
A "Scan tool" displays temperature of the air entering
the engine and
should read close to ambient air
temperature when engine
is cold, and rise as under
hood temperature increases.
If the engine has not
been run for several hours (overnight), the IAT sensor
temperature and
ECT readings should be close to each
other. A
failure in the IAT sensor circuit should set a
DTC 23. The DTC charts also contain a chart to check
for sensor resistance values relative to temperature.
Heated Oxygen Sensor (H02S)
The "Scan tool" has several positions that will indicate
the state
of the exhaust gases, Oxygen voltage,
integrator, and block learn. See "Scan tool" position
information in
"Introduction", "Driveability and
Emission," in this section.
A
problem in the oxygen sensor circuit, or fuel system,
should set a DTC 13 (open circuit), DTC 44 (lean
indication)/DTC 45 (rich indication). Refer to
applicable chart, if any of these DTC(s) were stored in
memory.
Throttle Position (TP) Sensor
A "Scan tool" displays throttle position in volts. On 3.2L
engine, Throttle position
(TP) sensor voltage should
read below 0.85 volts, with throttle closed and ignition
"ON", or at idle. Voltage should increase at a steady
rate
as throttle is moved toward wide open throttle.
The Engine
Control Module (ECM) has the ability to
auto-zero the TP sensor voltage if it is below about 0.85
volts. This means that any voltage less than 0.85 volts
will
be determined by the ECM to be 0% throttle.
Some
"Scan tools" have the ability to read the throttle
angle and should read 0%, when the throttle is closed.
A failure in the TP sensor or circuit should set a DTC 21.
Manifold Absolute Pressure (MAP) Sensor
"Scan tool" displays manifold pressure in volts. Low
pressure (high vacuum) reads a
low voltage, while a
high pressure
(low vacuum) reads a high voltage. A
failure in the Manifold Absolute Pressure (MAP) sensor
circuit
should set a DTC 33 and using the chart will find
the cause
of the problem. A DTC 33 may be set if a
rough or unstable
idle exists. CHART C-1 D can also be
used
to check MAP sensor.
Vehicle Speed Sensor (VSS)
A "Scan tool" reading should closely match with
speedometer reading with drive wheels turning. A
failure in the vehicle speed sensor circuit should set a
DTC 24.
AIR CONDITIONING (A/C) Request Signal
When air conditioning in "ON", the "Scan tool" should
indicate air conditioning "ON".
See
"Air Conditioning Compressor Clutch Control
System",
Section "6E2-C1 0" for A/C electrical system
diagnosis.
Power Steering Pressure (PSP) Switch
A "Scan tool" should read "OFF" normally, and "ON"
with high pressure. This reading may vary with
different "Scan tools". Refer to CHART C-1 E for power
steering pressure switch diagnosis.
Crankshaft Position (CKP) Reference Signal
The ignition control module sends a signal to the ECM,
which is used to calculate proper spark advance and
fuel delivery. A "Scan tool" will read this signal and is
displayed in revolution per minute.
See "Electronic
Ignition System",
Section "6E2-C-4" for more
information on the ignition system (ignition control).
Park/Neutral Position (PNP) Switch
A "Scan tool" should read park/neutral position when
in park, or neutral, and R-D, L, when in drive or
overdrive. This reading may vary with different makes
of tools. Refer to CHART C-1 A for park/neutral position
switch diagnosis.
Knock Sensor (KS)
A "Scan tool" will indicate when the knock sensor
module signals the ECM that knock is present. See
"Knock
Sensor System," Section "6E2-C5" for further
information on the knock sensor system.
ON-VEHICLE SERVICE
ENGINE CONTROL MODULE (ECM)
The ECM is programmed from the factory and has no replaceable calibration chip.
•

6E2-112 DRIVEABILITY AND EMISSIONS
CHART C-1E
POWER STEERING PRESSURE (PSP) SWITCH DIAGNOSIS
Circuit Description:
The Power Steering Pressure
(PSP) Switch is normally open to ground, and GRNIYEL wire will be near the battery
positive
voltage.
Turning the steering wheel increases power steering oil pressure and its load on an idling engine. The pressure
switch
will close before the load can cause an idle problem.
Closing
the switch causes GRN/YEL wire to read less than 1 volt. The Engine Control Module (ECM) will increase
the
idle air rate and disengage the air conditioning relay.
•
A pressure switch that will not close, or an open GRNIYEL wire, may cause the engine to stop, when power
steering loads are high.
• A switch that will not open or a GRNIYEL wire shorted to ground, may affect idle quality and will cause the air
conditioning
relay to be de-energized.
Test Description:
Numbers
below refer to circled numbers on the diagnostic chart.
CD Different makes of "Scan tools" may display the state of this switch in different ways. Refer to "Scan tool"
operator's manual to determine how this input is indicated.
® Checks to determine if GRNIYEL wire is shorted to ground.
@ This should simulate a closed switch.
POWER STEERING PRESSURE SWITCH ENGINE
CONTROL
MODULE(ECM)
I SIGNAL
r
BLU ---(~ BLU --+8 .. •f---BLU --{~ GRN/YEL ~ ~ B +
(LOCATED IN THE POWER
STEERING PUMP HIGH PASSENGERS CHASSIS PRESSURE LINE)
SIDE GROUND
FENDER
Fig. 6E2-65
•

MODES OF OPERATION
The Engine Control Module (ECM) uses voltage inputs
from several sensors to determine how much fuel to
give the engine. The fuel is delivered under one of
several conditions, called "modes". All the modes are
controlled by the ECM and are described below.
Starting Mode
When the ignition is first turned "ON", the ECM turns
"ON" the fuel pump relay for two seconds, and the fuel
pump builds up pressure. The ECM also checks the
Engine
Coolant Temperature (ECT) sensor and the
Throttle Position Sensor, and the determines the
proper
air/fuel ratio for starting. This ranges from 1.5:1
-36·c (-33.F) to 14.7:1, at 94•c (201.F) ECT.
The ECM controls the amount of fuel delivered in the
starting mode by changing
how long the injector is
turned
"ON" and "OFF". The is done by "Pulsing" the
injectors
for very short times.
Clear Flood Mode
If the engine floods, it may be cleared by pushing the
accelerator pedal down all the way. The ECM then will
fixed air/fuel ratio 16.5:1. The ECM holds this injector
rate
as long as the throttle stays wide open. If the
throttle position becomes less than approximately
70%, the ECM returns to the starting mode.
Run Mode
The run mode has two conditions called "Open Loop"
and "Closed Loop"
"Open Loop"
When the engine is first started, and it is above 500
Rovolution Per Minute (rpm), the system goes into
"Open Loop" operation. IN "Open Loop," the ECM
ignores the signal from the heated oxygen sensor
(H02S), and calculates the air/fuel ratio based on
inputs
from the ECT sensor and manifold absolute
pressure sensors.
The system stays in
"Open Loop" until the following
conditions are met:
1. The H02S has varying voltage output, showing
that
it is hot enough to operate properly. (This
depends on temperature.)
2. The ECT sensor is above a specified temperature.
3. A specific amount of time has elapsed after
starting the engine.
"Closed Loop"
The specific values for the above conditions vary with
different engines, and are stored in the ECM. When
these conditions are met, the system goes into
"Closed
Loop"
operation. In "Closed Loop", the ECM calculates
the air/fuel ratio (injector on-time) based on the signal
from the H02S. This allows the air/fuel ratio to stay
very close to 14.7:1.
DRIVEABILITV AND EMISSIONS 6E2-117
Acceleration Mode
The ECM responds to rapid changes in throttle position
and air
flow, and provides extra fuel.
Deceleration Mode
The ECM responds to changes in throttle position and
air
flow, and reduces the amount of fuel. When
deceleration is very fast, the ECM can cut off fuel
completely
for short periods.
Battery Positive Voltage Correction Mode
When battery positive voltage is low, the ECM can
compensate
for a weak spark delivered by the ignition
control module by:
• Increasing injector pulse width.
• Increasing the idle rpm.
• Increasing ignition dwell time.
Fuel Cutoff Mode
The fuel injectors are shut "OFF" if engine speed
"exceed" 6880 rpm (DOHC) or6800 rpm (SOHC). This is
to prevent damage to engine. When engine speed is
below 6880 rpm (DOHC) or 6800 rpm (SOHC), the fuel
injectors are again pulsed at a normal mode.

6E2 120 DRIVEABILITY AND EMISSIONS
THROTTLE BODY (TB) ASSEMBLY
The Throttle Body (TB) assembly is attached to the
intake manifold air
plenum, and is used to control air
flow into the engine, thereby controlling engine output
(Fig. 6E2-73). The TB within the TB is opened by the
driver through the accelerator controls. During engine
idle, the
TB is almost closed, and air flow control is
handled by the Idle Air Control (lAC) valve, described
below. To prevent
TB icing during cool weather
operation, engine
coolant is directed through a engine
coolant tube, part
of the TB, the engine coolant then
circulates through internal passageways around the
throttle bore and returns via the return engine coolant
tube.
The
TB also provides the location for mounting the
Throttle Position
Sensor. Vacuum ports the located at,
above or
below the throttle body to generate vacuum
signal needed
by various components.
Idle Air Control (lAC) Valve
Engine idle speed is controlled by the Engine Control
Module (ECM) through the Idle Air Control (lAC) valve
mounted on the
TB. The ECM sends voltage pulses to
the lAC motor windings causing the lAC valve pintle to
move "IN" or "OUT" a given distance (a step or count)
for each pulse. The pintle movement controls the
airflow around the TBs, which in turn, controls engine
idle speed.
• The "controlled" or desired idle speed for all
engine operating conditions is programmed into
the
calibration of the ECM. The programmed
engine speeds are based on engine coolant
temperature, park/neutral position switch status,
vehicle speed, battery positive voltage, and air
conditioning pressure (if equipped).
• The ECM "learns" the proper lAC valve positions to
achieve warm, stabilized idle speeds (revolution
per minute), desired
for the various conditions
(Park/Neutral position
or Drive, air conditioning
"ON" or "OFF", if equipped). This information is
stored in
ECM "Keep Alive" memories
(information
is retained after ignition is "OFF"). All
other lAC valve positioning is calculated based on
these
memory values.
As a
result, engine variations due to wear and
variations in
minimum TB position (within limits)
do not affect engine idle speeds. This system
provides correct idle control under
all conditions.
This also means
that disconnecting power to the
ECM can result in incorrect idle control or
necessity to partially depress the accelerator
pedal
when starting until the ECM relearns idle
control. Refer to note regarding clearing
memory
in "ECM and Sensors," Section "6E2-C1 ".
•
Engine idle speed is a function of total airflow into
the engine based on
lAC valve pintle position plus
TB opening plus calibrated vacuum loss through
accessories.
• The minimum TB position is set at the factory with
a stop screw. This setting allows enough air flow
by the TB to cause the lAC valve pintle to be
positioned a calibrated
number of steps (counts),
from the seat, during "controlled" idle operation.
The
minimum TB position setting on this engine
should not be considered the
"minimum idle
speed", as on other fuel injected engines. The
throttle stop
screw is covered with a plug at the
factory
following adjustment.
U7 CAUTION:
VI Do not attempt to remove the protective cap and
readjust the stop screw before
reviewi~g t~e
"Minimum TB Position Check", later m th1s
section. Misadjustment may result in damage to
the lAC valve or TB.
Fig. 6E2-73
2. Throttle body assembly
3. Throttle position sensor (TPS)
• The ECM normally resets the lAC valve pintle
position once during each ignition cycle,
when
vehicle speed increases above 35 miles per hour
on moderate acceleration. During the reset, the
ECM commands the lAC valve pintle to retract
completely, then move
"IN" to the seated position
(to establish the zero
count position), and then
back
out to the desired position. If, after the reset,
the
ECM is able to control the idle speed within the
calibrated count range, the
lAC valve will not be
reset again until the ignition has been turned
"OFF", the engine restarted and the car then
driven above 35 mile per hour.
If the ECM is not
able to control idle speed within the calibrated
count range after the first reset, the
ECM assumes
the
lAC valve pintle position is "lost", and enables
another reset
to occur. This will continue until the
pintle position is relearned.
• If the lAC valve is suspected as being the cause of
improper idle speed, perform a functional check of
the lAC valve (CHART C-2C) as described later in
this section.
-----------------------------'
•

Throttle Position (TP) Sensor
The Throttle Position (TP) Sensor is mounted on the
side
of the throttle body opposite the throttle lever
assembly.
Its function is to sense the current throttle
body position and relay that information to the ECM.
Knowledge ofTP is needed by the ECM to generate the
proper injector pulse width.
If the TP sensor senses a
Wide
Open Throttle, a voltage signal indicating this
condition is transmitted to the
ECM. The ECM will
widen the injector pulse, or increase the repetition rate,
permitting increased fuel
flow to each for the six fuel
injectors located in the fuel fail. As the throttle shaft
rotates in response to
movement of the accelerator
pedal (opening
or closing of the throttle body), the
throttle shaft transmits throttle
movement to the TP
sensor. A potentiometer (variable resistor) within the
TP sensor assembly creates a voltage that varies in
response to
TP. By applying a reference voltage (+5
VDC) to the TP sensor input, a varying voltage
(reflecting
TP) is available at the TP sensor output. The
voltage
output from the TP sensor is sent to the ECM
for use in determining current TP.
For further information ofTP sensor, refer to "ECM and
Sensors", Section
"6E2-C1 ". The TP sensor is an auto
zeroing type and cannot
be adjusted.
DRIVEABILITY AND EMISSIONS 6E2-121
INDUCTION AIR CONTROL PLATE
SYSTEM (DOHC) (Fig. 6E2-74)
This system consists of the Induction Air control plate
valve mounted in the common chamber
duct and a
vacuum operated diaphragm
which moves the Induction Air
Control Plate linkage. The vacuum to the diaphragm is
turned
"ON" or "OFF" by a vacuum switching solenoid
which is electrically operated by the
ECM.
Refer to CHART C-20 for diagnosing the Induction air
control plate system.
Manifold vaccum
1
Vacuum actuator
Induction air control plate valve
(noma! open)
Fig. 6E2-74
Engine control module (ECM)
Ignition switch
Canister, EGR, A.I.R. solenoids
DIAGNOSIS
FUEL METERING SYSTEM
Some failures of this system will result in the symptom,
"Engine Cranks But Will Not Run". If this condition
exists, see CHART A-3. This chart will determine
if the
problem is caused by the ignition system,
ECM or fuel
pump circuit.
If it's determined to be a fuel problem.
CHART A-5
or A-7 will be used. This includes the
injectors, fuel pressure control valve, fuel
pump and
fuel pump relay. The fuel system
wiring schematic
diagram is covered on the facing page
of CHART A-5.
If a malfunction occurs in the fuel control system, it
usually results in either a rich or lean Heated Oxygen
Sensor (H02S) signal condition. This condition is
sensed by the
H02S and the ECM will change the fuel
calculation (injector pulse width) based on
H02S input.
The change made to the fuel calculation will be
indicated
by a change in the block learn values which
can be displayed on a
"Scan tool". The ideal block learn
values are around 128 counts.
If the H02S senses a
lean condition, the
ECM will add fuel, resulting in a
block learn value above 128 counts.
If the H02S senses
a rich condition, the
ECM will subtract fuel, resulting in
a block learn value below 128 counts.
Block learn values can vary greatly, depending on
temperature, altitude and individual engine
tolerances. The programmed range for block learn
values is
58 to 198. Values within this range indicate
the system is in
"control". If a system is operating near
the extremes
of the block learn range during normal vehicle
operation, and there is a driveability complaint,
the fuel metering system should be checked. Refer to
the diagnostic trouble code
45 chart on the facing page
for potential causes of a rich condition (low block learn
values). Refer to the diagnostic trouble code 44 chart
facing page
for potential causes of a lean condition
(high block learn values).
If a driveability symptom
exists, also refer to the particular symptom in
"Symptoms", Section "6E2-B" for additional items to
check.
FUEL SYSTEM PRESSURE TEST
A fuel system pressure test procedure is included in
CHART A-7 under
"Fuel System Diagnosis" in "Engine
Components/Wiring Diagrams/Diagnostic
Charts",
Section "6E2-A" diagnostic charts.
IDLE AIR CONTROL (lAC) VALVE
A "Scan tool" will display Idle Air Control (lAC) valve
position in
"Counts" or steps. "0" steps indicates the
ECM is commanding the lAC valve to be driven all the
way in, to a fully seated position. This condition is
usually caused by a vacuum leak.
The higher the number
of counts, the more air is being
allowed to pass the
lAC valve. A functional check of the
lAC valve system (CHART C-2C) is provided in this
section. Refer to
"Refer, Unstable, or Incorrect Idle,
Stalling"
in "Symptoms", Section "6E2-B" for other
possibilities
for the cause of idle problems.

RESULTS OF INCORRECT OPERATION
An open or ground in the Ignition Control (I C) or bypass
circuits
will set a Diagnostic Trouble Code (DTC) 42 and
cause the engine
to run on the Ignition Control Module
(ICM)
timing.
The Engine
Control Module (ECM) uses information
from the Intake Air Temperature (IAT) and engine
coolant sensors in addition to revolution per minute
(rpm) to
calculate spark advance as follows:
• Cold
engine -more spark advance.
• Engine under minimum load based on rpm and
low amount of air flow = more spark advance.
• Hot engine = less spark advance.
• Engine under heavy load based on rpm and high
air
flow = less spark advance.
HOW DIAGNOSTIC TROUBLE CODE (DTC)
42 IS DETERMINED
When the system is running on the ICM, that is, no
voltage on the bypass line, the ICM grounds (GND) the
IC signal. The ECM expects to see no voltage on the IC
line during this condition.lf it sees a voltage, it sets DTC
42 and will not go into the IC mode.
DRIVEABILITY AND EMISSIONS 6E2-139
When the rpm for IC is reached (about 400 rpm) the
ECM applies 5 volts to the bypass line and the IC should
no longer be grounded in the ICM so the IC voltage
should
be varying.
An open in the
IC circuit while running, will result in the
engine continuing to run, but in a back-up
ig~it~on
timing mode (module timing) at a calculated t1mmg
value
and the malfunction indicator lamp will not be
"ON".
If
the IC circuit is shorted to GND, the "Check Engine"
malfunction
indicator lamp will be turned "ON", and a
DTC 42 will be set and the engine will operate in
module timing. Either condition may cause poor
performance and reduced
fuel economy.
If the bypass line is open or GND, the ICM will not
switch to IC mode so the IC voltage will be low and DTC
42 will be set.
If the IC line is grounded, the ICM will switch to IC, but
because the line isGNDtherewill be no ICsignai.A DTC
42 will be set.
DIAGNOSIS
If the engine cranks but will not run, CHART A-3 will be
used to determine if the Electronic Ignition (EI) system
is the cause
of the problem or if it is another part of the
fuel injection system.
If DTC 42 is set, that DTC chart should be used for
diagnosis. If no DTC is set and the ignition system is
suspected, use
CHART C4-D ("EI" Misfire) for
diagnosis.
DIAGNOSTIC TROUBLE CODE (DTC) 12
DTC 12 is used during the on-board diagnostic system
check procedure to test the
DTC display ability of the
ECM. This diagnostic trouble code indicates that the
ECM is not receiving the engine speed (REFERENCE)
signal. This occurs with the ignition key "ON" and the
engine not running.
The "reference"
signal also triggers the fuel injection
system.
Without the "reference" signal the engine
cannot run.
ON-VEHICLE SERVICE
ELECTRONIC IGNITION (EI) ASSEMBLY
1••1 REMOVE OR DISCONNECT
1. Negative battery cable
2. "EI" electrical connectors (3)
3. Spark plug wires. (Note wire positions to proper
coils) (6)
4. "EI" assembly to bracket bolts (3)
5. "EI" assembly from Intake Plenum.
1••1 INSTALL OR CONNECT
1. "EI" assembly bracket to Intake Plenum
Tighten bolts to 25 N·m (19 lb·ft)
2. Spark plug wires to correct spark plugs
3. "EI" electrical connectors
4. Negative battery cable

6E2-146 DRIVEABILITY AND EMISSIONS
SECTION C-5
KNOCK SENSOR (KS) SYSTEM
(DOHC ONLY)
CONTENTS
General Description ..................... 6E2-146 On-Vehicle Service ...................... 6E2-147
Purpose
............................ 6E2-146 Knock Sensor (KS) System ............... 6E2-147
Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 6E2-146 Knock
Sensor
(KS) Module .............. 6E2-147
Diagnosis
............................. 6E2-146 Chart C-5 Knock Sensor (KS) System Check ... 6E2-148
Results
Of Incorrect Knock Sensor (KS)
System Operation .................... 6E2-146
GENERAL DESCRIPTION
PURPOSE
To control spark knock, a Knock Sensor (KS) system
has been added. This system is designed to retard
spark timing up to
20·, to reduce spark knock in the
engine. This
allows the engine to use maximum spark
advance to improve driveability and fuel economy.
Varying octane
levels in gasoline can cause detonation
in engines. Detonation
is called spark knock.
OPERATION
The KS system has two major components:
• KS Module
• KS System
The sensor is mounted in the engine block under the
Intake Manifold assembly. When the KS detects
abnormal vibration (spark knocking) in the engine,
it
produced a voltage that is received by the KS module.
As long
as the KS module sees no voltage from the KS
(knock not present), it sends a signal voltage (8 to 10
volts) to the Engine Control Module (ECM) and the ECM
provides normal spark advance.
When the module detects voltage
from the KS (knock
present),
it turns "OFF" the signal to the ECM and the
voltage at terminal
"D1 0" goes toO volts. The ECM then
retards ignition control
(IC) to reduce spark knock.
The
KS signal line has a shield wire to prevent any false
signals to the
KS module. If the shield wire loses it
ground a false diagnostic trouble code (DTC) 43 may
result
or the ignition timing maybe retard needlessly.
DIAGNOSIS
RESULTS OF INCORRECT KNOCK SENSOR
(KS) SYSTEM OPERATION
Loss of the KS signal or loss of ground at KS module
would cause the signal to the ECM to remain high. This
condition
would cause the ECM to control IC, as if no
spark knocking were happening. No retard
would
occur, and spark knocking could become severe under
heavy engine load conditions. Loss
of the KS signal
to the ECM would cause the ECM
to constantly retard IC. This could result in sluggish
performance and cause a
DTC 43 to set.
A
"Scan tool" will read KC signal in A/D counts. When
detonation is detected,
KC signal counts will
increment, as long as knock is present. "Scan tools"
will
indicate knock being present either by showing
AID counts, or displaying "Yes" (knock present), or
"No" (knock not present). If DTC 43 is present, use that
chart to diagnose system. If no DTC is present and KS
system is suspected, use CHART C-5.
•

DRIVEABILITV AND EMISSIONS 6E2-161
SECTION C-1 0
AIR CONDITIONING (A/C) COMPRESSOR CLUTCH CONTROL
SYSTEM
CONTENTS
General Description ..................... 6E2-161 On-Vehicle Service ...................... 6E2-161
Operation ........................... 6E2-161 Chart C-10 Air Conditioning (A/C) System
Diagnosis ............................. 6E2-161 Functional Check ...................... 6E2-162
GENERAL DESCRIPTION
OPERATION
This system consists of a high pressure cut-out switch,
Air Conditioning (A/C) compressor
relay, A/C thermo
switch relay, A/C controller and the compressor.
The high pressure cut-out switch
(normally closed),
opens when the head pressure gets too high. This will
disable
the A/C clutch, before damage can occur to the
compressor or other
A/C components.
When
A/C control switch is "ON" and the high pressure
switch and thermo switch are
closed, a request signal
is sent to the Engine Control Module (ECM). The ECM
will then energize the A/C clutch through the A/C
clutch relay. The A/C controller which is separate from
the ECM will then turn the A/C cooling fan "ON".
The A/C controller controls the A/C cooling fan, as well
as sending a signal to the ECM on model equipped with
automatic transmission.
The
ECM will disable the A/C clutch during Wide Open
Throttle,
or high power steering loads. The ECM has a
slight delay for clutch engagement to allow for the idle
to slightly increase. Refer to CHART C-1 0 for wiring and
circuit description.
DIAGNOSIS
Chart C-10 should be used for the electrical portion of
the A/C circuit. Section 1 B should be used for
diagnosing the refrigerant portion of the system. The
"Scan tool" will be used in diagnosing the system, as it
has the ability to read the A/C request inputto the ECM,
as well as displaying when the ECM has commanded
the
A/C clutch "ON".
ON-VEHICLE SERVICE
For removal and replacement of A/C components,
refer to
A/C (SECTION 1 B) in this Manual.