check engine light ISUZU TROOPER 1995 Service Manual

Q)
DRIVEABILITV AND EMISSIONS 6E2-67
DIAGNOSTIC TROUBLE CODE (DTC) 21 B
THROTTLE POSITION (TP) SENSOR CIRCUIT
(SIGNAL
VOLTAGE LOW)
• THROTTLE CLOSED.
DOES "SCAN TOOL" DISPLAY THROTTLE POSITION (TP) SENSOR 0.2V· (200mV) OR BELOW?
~ $
• DISCONNECT TP SENSOR. • IF TP SENSOR
SIGNAL VOLTAGE INDICATES "HIGH" JUMPER 5V REFERENCE AND TP SENSOR SIGNAL VOLTAGE
ABOVE 4.0 VOLTS, REFER TO DIAGNOSTIC CKT TOGETHER. TROUBLE CODE 21A. "SCAN TOOL" SHOULD DISPLAY TP SENSOR OVER • DIAGNOSTIC TROUBLE CODE 21 IS INTERMITTENT.
4.0V IF NO ADDITIONAL DIAGNOSTIC TROUBLE CODES
DOES IT? WERE STORED, REFER TO "DIAGNOSTIC AIDS" ON FACING~.
LfJ ~
• PROBE TP SENSOR SIGNAL CKT WITH A TEST @ • REFER To FACING EAe'E'1oR J LIGHT CONNECTED TO BATTERY POSITIVE SPECIFIC INSTRUCTIONS.
VOLTAGE.
"SCAN TOOL" SHOULD DISPLAY TP SENSOR
OVER 4.0V
DOES
IT?
~ $
5V REFERENCE CKT OPEN OR SHORTED TO GROUND TP SENSOR SIGNAL CKT OPEN OR
OR SHORTED TO GROUND, OR SHORTED FAULTY CONNECTION
TO SENSOR GROUND CIRCUIT OR
OR FAULTY ENGINE CONTROL MODULE. FAULTY ENGINE CONTROL MODULE CONNECTION OR FAULTY ENGINE CONTROL MODULE.
CLEAR
DIAGNOSTIC TROUBLE CODES AND CONFIRM "CLOSED LOOP" OPERATION AND NORMAL "CHECK ENGINE" MALFUNCTION
INDICATOR LAMP OPERATION.

6E2-74 DRIVEABILITY AND EMISSIONS
Circuit
Description:
DIAGNOSTIC TROUBLE CODE (DTC) 32
EXHAUST GAS RECIRCULA TION(EGR) CIRCUIT
Exhaust Gas Recirculation (EGR) valve operation is Engine Control Module (ECM) controlled. The ECM will ground
the vacuum switch
valve (VSV) to turn the EGR valve "ON" and "OFF". An EGR Back Pressure Transducer
determines how
long the EGR valve stays "ON" based on Exhaust Back Pressure supplied to the Transducer thru
Tube
"S". The ECM monitors the Integrator to determine it the EGR system is functioning. The ECM will command
the
EGR valve "OFF" briefly when the EGR is suppose to be "ON", the Integrator will change at leastthree (3) counts
indicating the
EGR valve did "close" when commanded. The ECM will then recheck the system again by
commanding
EGR valve "ON" when it should not be "ON" and again monitors the Integrator for at least a three (3)
counts change indicating the EGR valve did come "ON" when commanded. If the EGR system fails this test five (5)
times a malfunction diagnostic trouble code 32 will be logged and the malfunction indicator lamp will be "ON".
Test Description: Number(s) below refer to circled ® Check operation of ECM circuit to EGR valve VSV.
number(s} on the diagnostic chart. The EGR valva chart is a check of the EGR system. If the
CD Checks the EGR valve will open and EGR passage EGR system works properly, check other items that
is not restricted. could result in high Block Learn valve. The EGR valve
® Check that EGR valve VSV is operating properly. passage being slightly restricted may cause diagnostic
® Checks the EGR Back Pressure Transducer oper-trouble code 32 to set.
ation.
• A sluggish Heated Oxygen Sensor may also cause
@ Test voltage source as well to EGR valve VSV. this diagnostic trouble code to be set falsely.
@ Check EGR Back Pressure Transducer for proper
operation.
EGR VALVE EGRV
~
BACK
PRESSURE
TRANSDUCER
vsv
~ EGRVALVE VACUUM SWITCHING
VALVE (VSV)
ENGINE HARNESS
CONNECTOR
'+--+-' (BLU) WHT
GRN AS
f fl "'I" ___.. TO IGN PORTED VACUUM
Fig. 6E2-42
ENGINE HARNESS
CONNECTOR
(BLU)
ENGINE CONTROL
MODULE(ECM)
EGR VALVE VSV DRIVER
•

DRIVEABILITV AND EMISSIONS 6E2-75
DIAGNOSTIC TROUBLE CODE (DTC) 32
EXHAUST GAS RECIRCULATION(EGR) CIRCUIT
• FIRMLY GRASP TOP OF EXHAUST GAS RECIRCULATION (EGR} VALVE AND CHECK FOR LOOSENESS BY TRYING TO
ROTATE VALVE IN BOTH DIRECTIONS.
IS LOOSENESS FELT?
l
$
-[$J
• PLACE TRANSMISSION IN "PARK" OR "NEUTRAL". REPLACE EGR VALVE I • RUN WARM ENGINE AT IDLE. ASSEMBLY
• ENGINE TEMPERATURE MUST BE ABOVE 60'C (120'F). • DISCONNECT VACUUM HOSE TO EGR VALVE. • APPLY 10"1NCHES OF VACUUM TO EGR VALVE. • ENGINE SHOULD RUN ROUGH AND/OR STALL.
DOES IT?
I
$ $
•
CONNECT VACUUM GAGE TO EGR SIDE OF VACUUM • REMOVE EGR VALVE AND CLEAN SWITCHING VALVE (VSV). ASSEMBLY.
• INCREASE ENGINE SPEED ABOVE 2000 REVOLUTION • REPLACE
VALVE IF NECESSARY. PER MINUTE.
SHOULD HAVE AT LEAST 10 INCHES OF VACUUM. DOES IT!
I
$ $
• DATA LINK CONNECTOR GROUNDED . @ • INSTALL VACUUM GAUGE TO THE
• ENGINE IDLING CHECK VACUUM SOURCE VACUUM HOSE AT THE EGR VALVE. BEFORE EGR MODULATOR. • INCREASE ENGINE SPEED TO ABOVE 2000 . SHOULD HAVE AT LEAST 10" OF VACUUM. AT LEAST 10" OF VACUUM. DOES IT? DOES IT!
I
I
$ $ $ ~
REFER TO @ • IGNITION "ON", ENGINE "OFF". EGR SYSTEM • INSPECT BACK PRESSURE
"DIAGNOSTIC • TEST LIGHT TO GROUND. WORKING PROPERLY. TUBE "S" FOR DAMAGE OR AIDS" ON
.
• BACKPROBE VOLTAGE SOURCE NO
TROUBLE FOUND. RESTRICTION. FACING'¢{ TO EGR VALVE VSV
SOLENOID. •
INSPECT VACUUM HOSE
TEST LIGHT SHOULD BE "ON". FROM THE EGR
IS IT? MODULATOR TO THE EGR
I VALVE FOR DAMAGE OR
$ $
RESTRICTION. IF OK, REPLACE EGR MODULATOR.
@ • REPEAT ABOVE TEST WITH TEST
OPEN IN I LIGHT TO BATTERY POSITIVE CIRCUIT VOLTAGE.
• BACKPROBE EGR VALVE VSV
SOLENOID ENGINE
CONTROL MODULE CIRCUIT.
TEST LIGHT SHOULD
BE "ON". IS IT?
I
$ $
RESTRICTED VACUUM SOURCE OPEN
IN CIRCUIT OR OR FAULTY SOLENOID FAULTY ENGINE
CONTROL MODULE

CD
®
DRIVEABILITY AND EMISSIONS 6E2-77
DIAGNOSTIC TROUBLE CODE (DTC) 33A
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR CIRCUIT
(SIGNAL
VOLTAGE HIGH-LOW VACUUM)
• IF ENGINE IDLE IS ROUGH, UNSTABLE, OR INCORRECT, CORRECT CONDITION BEFORE USING CHART. SEE "SYMPTOMS" IN SECTION "B". • ENGINE IDLING
• DOES "SCAN TOOL" DISPLAY A MANIFOLD ABSOLUTE PRESSURE (MAP)
VOLTAGE OF 4.0 VOLTS OR OVER?
~ $
• IGNITION "OFF". •
DOES "SCAN TOOL" DISPLAY
• DISCONNECT MAP SENSOR ELECTRICAL CONNECTOR. MAP SENSOR VOLTAGE LESS
• IGNITION "ON". THAN 1 VOLT? • "SCAN TOOL" SHOULD READ A VOLTAGE OF 1 VOLTS I OR LESS.
DOES IT?
$ $
DIAGNOSTIC TROUBLE
CODE l REFER TO J (DTC) 33A DTC
33B CHART. IS INTERMITTENT. IF NO ADDITIONAL DTC(S) WERE STORED, REFER TO "DIAGNOSTIC AIDS" ON FACING ~-
~ $
• PROBE SENSOR GROUND CIRCUIT WITH MAP SIGNAL CKT SHORTED TO A TEST LIGHT TO BATTERY POSITIVE VOLTAGE,
SHORTED TO 5 VOLT
VOLTAGE. REFERENCE CKT, OR FAULTY • TEST LIGHT SHOULD LIGHT. ENGINE CONTROL MODULE.
DOES IT?
$ $
PLUGGED OR LEAKING OPEN SENSOR GROUND CIRCUIT.
SENSOR VACUUM HOSE OR FAULTY MAP SENSOR.
CLEAR DTC(S) AND CONFIRM "CLOSED LOOP" OPERATION AND NORMAL "CHECK ENGINE" MALFUNCTION INDICATOR LAMP OPERATION.

DRIVEABILITY AND EMISSIONS 6E2-79
DIAGNOSTIC TROUBLE CODE (DTC) 338
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR CIRCUIT
(SIGNAL VOLTAGE LOW-HIGH
VACUUM)
CD • ENGINE IDLING
DOES "SCAN TOOL" DISPLAY MAP VOLTAGE BELOW .25 VOLTS?
@ • IGNITION "OFF".
• DISCONNECT SENSOR ELECTRICAL CONNECTOR.
•
JUMPER HARNESS TERMINALS "2" TO "1". • IGNITION "ON". • MANIFOLD ABSOLUTE PRESSURE VOLTAGE SHOULD READ OVER 4 VOLTS.
DOES IT?
@ • IGNITION "OFF"
• REMOVE JUMPER WIRE.
• PROBE TERMINAL "B" GREY /RED WIRE WITH 'W' A TEST LIGHT TO BATTERY POSITIVE VOLTAGE. • IGNITION "ON". • "SCAN TOOL" SHOULD READ OVER 4 VOLTS.
DOES IT?
5 VOLT REFERENCE CIRCUIT OPEN OR SHORTED
TO GROUND OR FAUL TV ENGINE CONTROL MODULE.
DTC 33B IS INTERMITTENT. IF NO ADDITIONAL DTC{S) WERE STORED, REFER TO "DIAGNOSTIC AIDS" ON FACING p
GRY/RED WIRE OPN OR GRY/RED WIRE SHORTED TO GROUND OR GRY/RED WIRE SHORTED TO SENSOR GROUND OR FAUL TV ENGINE CONTROL MODULE.
CLEAR DTC{S) AND CONFIRM "CLOSED LOOP" OPERATION AND NORMAL "CHECK ENGINE" MALFUNCTION INDICATOR LAMP OPERATION.

6E2-80 DRIVEABILITV AND EMISSIONS
Circuit Description:
DIAGNOSTIC TROUBLE CODE (DTC) 42
IGNITION CONTROL (IC) CIRCUIT
The Electronic Ignition (EI) module sends a reference signal (YEL/RED wire) to the Engine Control Module (ECM),
when the engine is cranking. While the engine speed is under 500 revolution per minute, the ignition control (IC)
module will control ignition timing. When the engine speed exceeds 500 revolution per minute, the ECM applies 5
volts to the bypass line to switch the timing to ECM control.
When the system is running on the El module, that is, no voltage on the bypass line, the El module grounds the IC
signal. The ECM expects to sense or detect no voltage on the IC line during this condition. If it senses or detects a
voltage,
it sets Diagnostic Trouble Code (DTC) 42 and will not go into the IC mode.
When the revolution per minute
for IC is reached (about 500 revolution per minute), voltage will be applied to the
bypass
line. The IC should no longer be grounded in the El module, so the IC voltage should be varying.
If the bypass line is open or grounded, the El module 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 El module will switch to IC but, because the line is grounded, there will be no IC signal.
A DTC 42 will be set.
Test Description: Number(s) below refer to circled
number(s) on the diagnostic chart.
CD DTC 42 means the ECM has detected an open or
short to ground in the IC or bypass circuits. This
test confirms
DTC 42 and that the fault causing the
DTC is present.
® Checks for a normaiiC ground path through the IC
module. An IC circuit wire, shorted to ground, will
also
read less than 500 ohms, however, this will
be checked later.
® As the test light voltage touches bypass circuit
wire, the
module should switch, causing the ohmmeter
to "over-range" if the
meter is in the
1000-2000 ohms position. Selecting the 10-20,000
ohms position will indicate above 5000 ohms. The
important thing is that the module
"switched."
® The module did not switch and this step checks
for:
• IC circuit wire shorted to ground.
• Bypass circuit wire open.
• Faulty IC module connection or module.
@ Confirms that DTC 42 is a faulty ECM and not an
intermittent in circuit wire or bypass circuit wire.
ENGINE CONTROL
MODULE(ECM)
~--------------------------VEL
~----------------------YE~RED
~----------------------YE~BLU
IC SIGNAL
REF HIGH
REF LOW
BY PASS YE~GRN D11
BLK/ORN ----)}-BLK!YEL ~ TO IGN
BLK/RED -TO TACHOMETER SWITCH
BLK ~ AND TCM (C91-D12)
WHT :' '1 CRANKSHAFT
BLK -----..~ ! POSITION
WHT/RED ',_; 1 SENSOR
"SHIELD
Fig. 6E2-45
..

6E2-82 DRIVEABILITY AND EMISSIONS
Circuit Description:
DIAGNOSTIC TROUBLE CODE (DTC) 43
KNOCK SENSOR (KS) CIRCUIT
(DOHC)
Knock Sensor (KS) is accomplished with a module that sends a voltage signal to the Engine Control Module (ECM).
As the KS detects engine knock, the voltage from the KS module to the ECM drops, and this signals the ECM to
retard timing. The ECM will retard the timing when knock is detected and revolution per minute is above about 880
revolution
per minute.
Diagnostic
Trouble Code (DTC) 43 means the ECM has been low voltage at CKT 010 for longer than 4.0 seconds
with the engine running or the system has
failed the functional check.
DTC 43 will set when:
• After run spark, more than 4 seconds
• KS input signal has been low more than 4 seconds
Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.
CD If the conditions for a DTC 43 are present the "Scan tool" will always display "YES". There should not be a
knock at
idle unless an internal engine problem, or a system problem exists.
® This test will determine if the system is functioning at this time. Usually a KS signal can be generated by
tapping on the right exhaust
manifold. If no KS signal is generated try tapping on block close to the area of the
sensor.
® Because DTC 43 sets when the signal voltage on CKT 010 remains low this test should cause the signal on
CKT to go high. The 12 volts signal should be seen by the ECM as "no knock" if the ECM and wiring are OK.
@ This test will determine if the KS signal is being detected on CKT WHT or if the KS module is at faulty.
@ If CKT WHT is routed is close to secondary ignition wires the KS module may see the interference as a KS
signal. ~
® This checks the ground circuitto the module. An open ground will cause the voltage on CKT 010 to be about 5
volts which would cause the DTC 43 functional test to fail.
(J) Contacting CKT WHT with a test light to 5 volts should generate a KS signal. This will determine if the KS
module is operating correctly.
Diagnostic Aids: DTC43 can be caused by a faulty connection atthe KS module or atthe ECM. Also check CKT
010 for possible open or short to ground.
Refer
to "lntermittents" in "Symptoms," Section "6E2-B".
TWO-WAY CONNECTOR
BLACK AT REAR OF INTAKE
-' / I I
WHT
BLK!YEL
LOCATED REAR OF 0 INTAKE PLENUM
1-----L T GRN/YEL
KNOCK
SENSOR
MODULE
BLK/YEL
GROUND
TOECM ~ TERMINAL ENGINE A12 GROUND
0 LOCATEDAT _ DRIVER'S SIDE REAR OF CYLINDER HEAD
Fig. 6E2-46
RED/GRN
+ TO MAIN RELAY
ENGINE CONTROL MODULE(ECM)
KNOCK SENSOR SIGNAL INPUT

CD
DRIVEABILITV AND EMISSIONS 6E2-83
• ENGINE IDLING.
DIAGNOSTIC TROUBLE CODE (DTC) 43
KNOCK SENSOR (KS) CIRCUIT
(DOHC)
• "SCAN TOOL" SET ON KNOCK SENSOR (KS} SIGNAL. IS THERE A KS SIGNAL INDICATED?
~ $
• DISCONNECT KS MODULE. ® • ENGINE IDLING.
• ENGINE IDLING. • TAP ENGINE BLOCK IN AREA OF KS. • PROBE HARNESS TERMINAL "C" (CKT • IS A KS SIGNAL INDICATED WHILE TAPPING ON
D10} WITH A TEST LIGHT CONNECTED
ENGINE?
TO 12 VOLTS. AFTER SECONDS, DOES "SCAN TOOL"
DISPLAY A KS SIGNAL?
$ ~ ~ ~ • IGNITION "ON". CKT D10 OPEN, @ • DISCONNECT KS MODULE. DIAGNOSTIC
TROUBLE
• PROBE TERMINAL SHORTED TO • PROBE HARNESS TERMINAL "D" CODE 43 IS INTERMITTENT. "D" WITH A TEST
GROUND, OR WITH A TEST LIGHT TO 12V. IF NO ADDITIONAL
LIGHT TO GROUND. FAULTY ENGINE DIAGNOSTIC TROUBLE
CONTROL CODES WERE STORED,
MODULE.
REFER TO "DIA~= AIDS" ON FAGIN .
I I
LIGHT "ON" I LIGHT "OFF" I LIGHT "ON" j LIGHT "OFF" I
I
I
• REMOVE TERMINAL TERMINAL "D" (J) • RECONNECT KS MODULE. REPAIR
OPEN GROUND I "E" FROM
OPEN, • DISCONNECT KS . CONNECTOR.
SHORTED TO • ENGINE IDLING.
• RECONNECT KS GROUND. • MOMENTARILY TOUCH KS MODULE.
HARNESS IS TERMINAL "E" • ENGINE IDLING. WITH A TEST LIGHT TO 12V. IS THERE A KS • EACH TIME THE TEST LIGHT
SIGNAL INDICATED?
CONTACTS TERMINAL "E", A KS SIGNAL SHOULD BE GENERATED. • IS A KS SIGNAL
INDICATED WITH "SCAN TOOL"?
~ $
~
FAULTY CONNECTION AT SENSOR TERMINAL "E" OPEN. OR FAULTY KS. SHORTED
TO GROUND,
~
FAULTY CONNECTION AT KS MODULE, OR FAULTY KS MODULE. FAULTY @ • IF AN AUDIBLE KNOCK CAN BE HEARD, CONNECTION
REPAIR INTERNAL ENGINE PROBLEM. IF OK, OR CHECK FOR ROUTING OF WIRE FROM KS TO KS MODULE. KS MODULE FOR PICKING UP FALSE KS SIGNALS FROM AN ADJACENT WIRE.
REROUTE AS NECESSARY. IF ROUTING IS CORRECT, REPLACE KS.

6E2-90 DRIVEABILITY AND EMISSIONS
INTERMITTENTS
Definition: Problem may or may not turn "ON" the
"Check Engine" malfunction indicator lamp or store
Diagnostic
Trouble Code (DTC).
DO NOT use the DTC charts in "Engine Components/
Wiring Diagrams/Diagnostic
Charts," Section "6E2-A"
for intermittent problem. The fault must be present to
locate the problem. If a fault is intermittent, use of DTC
charts may result in replacement of good parts.
•
• Most intermittent problems are caused by faulty
electrical
connections or wiring. Perform careful
visual/physical
check as described at start of
"Symptoms," Section "6E2-B." Check for:
Poor mating
of the connector halves. or
terminal not fully seated in the connector body
(backed out).
Improperly formed or damaged terminal. All
connector
terminals in the problem circuit
should be carefully reformed or replaced to
insure proper contact tension.
Poor
terminal to wire connection. This
requires removing the
terminal from the
connector body to check. Refer to
SECTION 8
"Wiring Harness Service,"
If a visual/physical check does not find the cause
of the problem, the car can be driven with a
voltmeter connected to a suspected circuit. A
"Scan tool" can also be used to help detect
intermittent conditions. An abnormal
voltage, or
"Scan" tool reading, when the problem occurs,
indicates the
problem may be in that circuit. If the wiring
and connectors check
OK, and a DTC was
stored
for a circuit having a sensor, except for
DTC(s) 44 and 45, substitute a known good sensor
and recheck.
• Loss of DTC memory. To check, disconnect
throttle position (TP) sensor and idle engine until
"Check
Engine" malfunction indicator lamp comes
"ON". DTC 21 should be stored, and kept in
memory when ignition is turned "OFF". If not, the
Engine
Control Module (ECM) is faulty.
•
An intermittent "Check Engine" malfunction
indicator
lamp with no stored DTC may be caused
by:
Ignition coil shorted to ground and arcing at
spark
plug wires or plugs.
"Check
Engine" malfunction indicator lamp
wire to ECM shorted to ground.
Diagnostic
"test" terminal wire to ECM,
shorted to ground.
ECM grounds, refer to ECM wiring diagrams.
• Check for an electrical system interference caused
by a defective
relay, ECM driven solenoid, or
switch. They can cause a sharp electrical surge.
Normally, the problem will occur when the faulty
component is operated.
• Check for improper installation of electrical
options such as lights, 2 way radios, etc.
• Ignition control wires should be routed away from
spark plug wires, electronic ignition (EI) wires, El
housing, coil and generator. Ground wire from
ECM to El should have a good connection.
• If problem has not been found, refer to "ECM
Connector Symptom" charts at the end of
"Symptoms," Section "6E2-B."
HARD START
Definition: Engine cranks OK, but does not start for a
long time. Does eventually run, or may
start
but immediately dies.
PRELIMINARY CHECKS
• Perform the careful visual/physical checks as
described at start of "Symptoms," Section "6E2-
B".
•
Make sure the driver is using the correct starting
procedure.
SENSORS
• CHECK: Engine coolant temperature sensor using
a
"Scan tool", compare engine coolant
temperature with ambient temperature
on
cold engine. -
If engine coolant temperature
readings
is 5 degrees greater than or less than
ambient air temperature on a
cold
engine, check resistance in engine
coolant temperature sensor circuit
or
sensor itself. Compare engine coolant
temperature sensor resistance value
to the "Diagnostic Aids" chart on
DTC
14 chart.
• CHECK: Manifold absolute pressure sensor.
Check for flooding and/or correct sensor
for vehicle.
• CHECK: TP sensor for binding or a high TP sensor
voltage with the throttle closed (should
read between 0.54 volt and 1.25 volts.)

6E2-94 DRIVEABILITY AND EMISSIONS
3. If there is no revolution per minute (rpm) drop
on one or more cylinders, or excessive
variation is drop, check
for spark on the
suspected
cylinder(s) using a shop
oscilloscope or with J 26792 (ST-125) spark
tester
or equivalent. If no spark, refer to
ENGINE ELECTRICAL (SECTION 6D) for
intermittent operation of miss. If there is a
spark, remove spark
plug(s) in these cylinders
and check for:
-
Insulator Cracks.
- Wear.
-
Improper Gap.
- Burned
Electrodes.
-Heavy Deposits.
• CHECK: Spark plug wires by connecting
ohmmeter to ends of each wire in
question.
If meter reads over 30,000
ohms, replace wire(s).
FUEL SYSTEM
• CHECK: Fuel system -Plugged fuel filter, low
pressure. Use CHART A-7.
• CHECK: Contaminated fuel.
• CHECK: Injector drivers. Disconnect all injector
harness connectors. Connect
J 34730-2
Injector Test Light or equivalent 6 volts
test light between the harness terminal,
of each injector connector and note light
while
cranking. If test light fails to blink at
any connector, it is a faulty injector drive
circuit harness, connector
or terminal.
ENGINE MECHANICAL
• CHECK: Compression. Perform compression
check on
questionable cylinder(s) found
above.
If compression is low, repair as
necessary. Refer to ENGINE
MECHANICAL DIAGNOSIS (SECTION
6A).
• CHECK: Engine parts. Remove cam covers.
Check
for broken valve springs, worn
camshaft lobes and valve timing. Repair
as necessary. See ENGINE MECHANICAL
DIAGNOSIS (SECTION
6A).
ADDITIONAL CHECKS
• CHECK: For electromagnetic interference (EMI).
A missing condition can be caused by EMI
on the reference circuit. EMI can usually
be detected by monitoring engine speed
with a "Scan tool". A sudden increase in
rpm
with little change in actual engine
speed change, indicates
EMI is present. If
the problem exists, check routing of
secondary wires, check distributor
ground circuit.
• CHECK: Intake and exhaust manifold passage for
casting
flash.
ROUGH, UNSTABLE, OR INCORRECT IDLE, STALLING
Definition: Engine runs unevenly at idle. If severe, the
engine
or car may shake. Engine idle
speed may vary in rpm. Either condition
may be severe enough to stall engine.
PRELIMINARY CHECKS
• Perform the careful visual/physical checks as
described at start
of "Symptoms," Section "6E3-
B."
• CHECK:
• CHECK:
For vacuum leaks
Engine control module (ECM) grounds for
being clean, tight and proper routing.
See ECM wiring diagrams.
FUEL SYSTEM
• NOTICE: Monitoring L.T. Fuel Trim will help
identify the cause of the problem. If the
system is running
lean (LT. Fuel Trim
greater than 142), refer
to "Diagnostic
Aids"
on facing page of diagnostic trouble
code 44.
If the system is running rich (L.T. Fuel
Trim less than 118), refer to "Diagnostic
Aids" on facing page of diagnostic trouble
code 45.
• CHECK:
• CHECK:
• CHECK:
• CHECK:
• CHECK:
Incorrect minimum idle speed may be
caused
by foreign material accumulation
in the throttle bore coking, on the throttle
body or on the throttle shaft.
Clean injectors.
For
fuel in fuel pressure control valve
hose. If fuel is present, replace regulator
assembly.
Evaporative Emission Control System,
refer to "Evaporative Emission Control
System," Section "6E2-C3".
The Heated oxygen sensor should
respond quickly to different throttle
position, if it does not, check the heated
oxygen sensor
for silicon contaminations
from fuel, or use of improper RTV sealant.
The sensor will have a white, powdery
coating and will result in a high but false
signal voltage
(rich heated oxygen sensor
signal indication). The ECM will then
reduce the
amount of fuel delivered to the
engine, causing a severe
driveability
problem.
II