engine ISUZU TROOPER 1995 Workshop Manual

6E2-84 DRIVEABILITY AND EMISSIONS
DIAGNOSTIC TROUBLE CODE (DTC) 44
HEATED OXYGEN SENSOR (H02S) CIRCUIT
(LEAN HEATED OXYGEN SENSOR (H02S) SIGNAL INDICATED)
Circuit Description:
The engine control module supplies a voltage of about .43 volt between terminals "83" and "82". (If measured
with a
10 megohm digital voltmeter, this may read as low as .32 volts.) The Heated Oxygen Sensor (H02S) varies
the
voltage within a range of about 1 volt, if the exhaust is rich, down through about .1 0 volt, if exhaust is lean.
The sensor is like an open circuit and produces no voltage, when it is below about 360°C (600°F). An open sensor
circuit,
or cold sensor, cause "Open Loop" operation.
Test Description:
Numbers below refer to circled numbers on the diagnostic chart.
CD Diagnostic Trouble Code (DTC) 44 is set, when the 02S signal voltage is fixed below .1 00 mV and the
following:
• Throttle
position sensor greater than 9.8%.
• No DTC 21 or 33. • Oxygen signal voltage is steady between .347
volt and .547 volt.
•
The engine has been running at least for 180 •
seconds. • • System is operating in "Closed Loop". •
Engine Operation Temperature 69SC (155°F).
All of the above conditions present for 25 sec .
Integrator not at 128 .
Diagnostic Aids:
Using the "Scan tool", observe the block learn value at different revolution per minute. The "Scan tool" also
displays
the block cells, so the block learn values can be checked in each ofthe cells, to determine when the DTC 44
may have been set.
If the conditions for DTC 44 exist, the block learn values will be around 150.
•
Check for ground in wire between connector sensor.
• Fuel Contamination-Water, even in small amounts, near the in-tank fuel pump inlet can be delivered to the
injector. The water causes a
lean H02S signal and can set a DTC 44.
• Fuel Pressure-System will be lean if pressure is too low. If may be necessary to monitor fuel pressure,
while driving the car at various road speeds and/or loads to confirm. See Fuel System diagnosis CHART A-5.
• Exhaust Leaks -lfthere is an exhaust leak, the engine can cause outside air to be pulled into the exhaust and
past the sensor.
Vacuum or crankcase leaks can cause a lean condition.
• If DTC 44 is intermittent, refer to Section "6E2-8".
• Fuel
Injectors-The wrong fuel injector(s) could be the cause of a lean H02S signal condition. Verify that the
correct
fuel injector(s) are installed in the vehicle. Refer to the service parts manual for correct part and part
number.
Refer
to "Engine Control Module and Sensors", Section "6E2-C1" for proper diagnosis.
TRANSMISSION
HARNESS
CONNECTOR
~BLK1
TRANSMISSION
HARNESS CONNECTOR
(BLUE) I /' BL~GRN~r-~----------~-------BLU
RED/BLU (MfT) --(( 1
1 ; « RED
(BLUE) ~
PASSENGER Q SIDE
LT BLU (A/T) L
WHT/RED 1
P:::l=t=t1 l BL~GRN ----.-----BL~GRN
BLK!YEL BL~BLU FENDER 02 --·S HEATER ELEMENT l
ENGINE
DRIVER'S SIDE BLOCK REAR AT CYLINDER
TRANSMISSION HARNESS _ HEAD CONNECTOR (BLUE)
10A -----BL~GRN ____ .,.... ~3EL PUMP RELAY
Fig. 6E2-47
ENGINE CONTROL
MODULE(ECM)
H02SGROUND REFERENCE
H02SSIGNAL
ECM GROUNDS
ECM GROUNDS
..

DRIVEABILITY AND EMISSIONS 6E2-85
DIAGNOSTIC TROUBLE CODE (DTC) 44
HEATED OXYGEN SENSOR (H02S) CIRCUIT
(LEAN HEATED OXYGEN SENSOR (H02S) SIGNAL INDICATED)
(j) •
RUN WARM ENGINE (69SC/155'F) AT 1200 REVOLUTIOM PER MINUTE
• DOES "SCAN TOOL" INDICATE OXYGEN (02) VOLTAGE FIXED BELOW 0.10 VOLTS (100 mV)
• DISCONNECT HEATED OXYGEN SENSOR (H02S).
• WITH ENGINE IDLING, "SCAN TOOL" SHOULD DISPLAY
H02S BETWEEN .35 VOLTS AND .55 VOLTS (350 mV AND 550 mV). DOES IT?
DIAGNOSTIC TROUBLE CODE 44 IS INTERMITTENT. IF NO ADDITIONAL DIAGNOSTIC TROUBLE CODES WERE STORED, REFER TO "DIAGNOSTIC AIDS" ON FACING I?,Aer.
H02S SIGNAL CKT SHORTED TO GROUND OR FAULTY ENGINE CONTROL MODULE
CLEAR DIAGNOSTIC TROUBLE CODES AND CONFIRM "CLOSED LOOP" OPERATION AND NORMAL "CHECK ENGINE" MALFUNCTION
INDICATOR LAMP OPERATION.

6E2-86 DRIVEABILITY AND EMISSIONS
DIAGNOSTIC TROUBLE CODE (DTC) 45
HEATED OXYGEN SENSOR (H02S) CIRCUIT
(RICH
HEATED OXYGEN SENSOR (H02S) SIGNAL INDICATED)
Circuit Description:
The Engine Control Module (ECM) supplies a voltage of about .45 volt between terminals "83" and "82". (If
measured with a 10 megohm digital voltmeter, this may read as low as .32 volts.) The Heated Oxygen Sensor
(H02S)
varies the voltage within a range of about 1 volt, if the exhaust is rich, down through about .1 0 volt, if
exhaust is lean.
The sensor is like an open circuit and produces no voltage, when it is below about 360"C (600"F). An open sensor
circuit,
or cold sensor, cause "Open Loop" operation.
Test Description:
Numbers below refer to circled numbers ·on the diagnostic chart.
CD Diagnostic Trouble Code (DTC) 45 is set, when the H02S signal voltage is fixed above .1 0 volts (1 00 mV) under
the
following conditions:
• Throttle position sensor greater than 9.8%. • 02 Signal Voltage is les than 0.347 volts and
• No DTC 21 A/21 8 or 33A/338. greater than .547 volts.
•
The engine is running for longer than 180 • Temperature above 69.5"C (155"F).
seconds. • Integrator not at 128
• System is operating in "Closed Loop". • All of the above condition present for 50 sec.
Diagnostic Aids:
The DTC 45, or rich H02S signal, is most likely caused by one of the following:
• Fuel Pressure-System will go rich, if pressure is too high. The ECM can compensate for some increase.
However,
if it gets too high, a DTC 45 will be set. See Fuel System diagnosis CHART A-5.
• HEI Shielding-An open ground CKT BLK/GRN may result in EMI, or induced electrical "noise". The ECM
looks at this "noise" as reference pulses. The additional pulses result in a higher than actual engine speed
signal. The ECM then delivers too much fuel, causing system to go rich. Engine tachometer will also, show ~
higher than actual engine speed, which can help in diagnosing this problem.
• Evaporate emission canister purge-Check for fuel saturation. If full of fuel, check canister control and
hoses.
See evaporate emission canister purge, Section "C3".
• Manifold absolute pressure (MAP) sensor-An output that causes the ECM to sense a higher than normal
MAP (low vacuum) can causethesystemto go rich. Disconnecting the MAP sensor will allow the ECMtoseta
fixed value for the MAP sensor. Substitute a different MAP sensor, if the rich condition is gone, while the
sensor is disconnected.
• Throttle position sensor-An intermittent throttle position sensor output will cause the system to go rich,
due
to a false indication of the engine accelerating.
• 02 sensor contamination -Inspect H02S for silicone contamination 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
H02S signal indication). The ECM will then reduce the amount of fuel delivered to the engine, causing a
severe surge driveability problem.
• Exhaust gas recirculation -Valve sticking open at idle, usually accompanied by a rough idle, or stall
complaint, especially at idle. Refer to CHART C-7A to check exhaust gas recirculation system.
If DTC 45 is intermittent, refer to Section "6E2-8".
TRANSMISSION
HARNESS
CONNECTOR ,[BLK1
TRANSMISSION
HARNESS CONNECTOR !BLUE I I ,, BLK!GRN~E----r:......,-----"*----BLU
RED/BLU (MfT) ~ 1
1 1 RED
(BLUE) ~
PASSENGER Q SIDE FENDER
L T
BLU (AfT) L WHT/RED 1
R=+=+=:R l BLK!GRN -----BLK!GRN
BLK/YEL BLK!BLU
1
ENGINE
BLOCK Q TRANSMISSION HARNESS -CONNECTOR (BLUE) -
DRIVER'S SIDE REAR AT CYLINDER HEAD
10A BLK/GRN -~~EL PUMP RELAY
Fig. 6E2-48
ENGINE CONTROL MODULE(ECM)
02SGROUND REFERENCE 02S SIGNAL
ECM GROUNDS
ECM GROUNDS
..

DRIVEABILITY AND EMISSIONS 6E2-87
DIAGNOSTIC TROUBLE CODE (DTC) 45
HEATED OXYGEN SENSOR (H02S) CIRCUIT
(RICH
HEATED OXYGEN SENSOR (H02S) SIGNAL INDICATED)
Q) • RUN WARM ENGINE (69.5"C/155"F) AT 1200 REVOLUTION PER MINUTE
• DOES "SCAN TOOL" DISPLAY HEATED OXYGEN SENSOR VOLTAGE FIXED ABOVE .75 VOLTS (750 mV)?
• DISCONNECT HEATED OXYGEN SENSOR AND JUMPER HARNESS CKT SYBLU TO GROUND.
• "SCAN TOOL" SHOULD DISPLAY OXYGEN BELOW
.35 VOLTS (350 mV). DOES IT?
DIAGNOSTIC TROUBLE CODE 45 IS INTERMITTENT. IF NO ADDITIONAL DIAGNOSTIC TROUBLE CODES WERE STORED, REFER TO "DIAGNOSTIC AIDS" ON FACING P
CLEAR
DIAGNOSTIC TROUBLE CODES AND CONFIRM "CLOSED LOOP" OPERATION AND NORMAL "CHECK ENGINE" MALFUNCTION
INDICATOR LAMP OPERATION.

6E2-88 DRIVEABILITY AND EMISSIONS
DIAGNOSTIC TROUBLE CODE (DTC) 51
ENGINE CONTROL MODULE (ECM) FAILURE ECM FAILED OR
ELECTRICALLY
ERASABLE PROGRAMMABLE READ ONLY MEMORY FAILURE)
CHECK THAT ALL ECM CONNECTIONS ARE GOOD
IF OK, CLEAR MEMORY AND RECHECK ECM.
IF CODE 51 REAPPEARS, REPLACE ECM.
CLEAR DIAGNOSTIC TROUBLE CODES AND CONFIRM "CLOSED LOOP" OPERATION AND NORMAL "CHECK ENGINE" MALFUNCTION
INDICATOR LAMP OPERATION.
Ill

DRIVEABILITY AND EMISSIONS 6E2-89
SECTION B
SYMPTOMS
CONTENTS
Important Preliminary Checks . . . . . . . . . 6E2-89
Before Starting . . . . . . . . . . . . . . . . . . . . . . 6E2-89
Symptom . . . . . . . . . . . . . . . . . . . . . . . . . . . 6E2-89
Visual/Physical Check . . . . . . . . . . . . . . . . 6E2-89
lntermittents . . . . . . . . . . . . . . . . . . . . . . . . 6E2-90
Hard Start . . . . . . . . . . . . . . . . . . . . . . . . . . 6E2-90
Surges and/or Chuggles .............. 6E2-91
Lack of Power, Sluggish, or Spongy . . . . 6E2-92
Detonation/Spark Knock .............. 6E2-92
Hesitation, Sag, Stumble . . . . . . . . . . . . . 6E2-93
Cuts Out, Misses . . . . . . . . . . . . . . . . . . . . . 6E2-93
Rough, Unstable, or Incorrect Idle,
Stalling ............................. 6E2-94
Poor Fuel Economy . . . . . . . . . . . . . . . . . . . 6E2-95
Excessive Exhaust Emissions or Odors .. 6E2-96
Backfire . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6E2-96
Dieseling, Run-on .................... 6E2-97
Restricted Exhaust System
Check (CHART B-1) ................... 6E2-98
IMPORTANT PRELIMINARY CHECKS
BEFORE STARTING
Before using this section you should have performed
the on-board diagnostic system check and determined
that:
1. The engine control module and "Check Engine"
malfunction indicator lamp are operating
correctly.
2. There are no diagnostic trouble codes stored, or
there is a diagnostic trouble code but no "Check
Engine" malfunction indicator lamp.
SYMPTOM
Verify the customer complaint, and locate the correct
symptom in the
table of contents. Check the items
indicated under
that symptom.
VISUAL/PHYSICAL CHECK
Several of the symptom procedures call for a Careful
Visual/Physical
Check. The importance of this step
cannot
be stressed too strongly -it can lead to
correcting a
problem witho'ut further checks and can
save
valuable time. This check should include: •
Engine control
module grounds for being clean,
tight and in their proper location.
•
Vacuum hoses for splits, kinks, and proper
connections,
as shown on "Vehicle Emission
Control Information" label. Check thoroughly for
any type of leak or restriction.
• Air leaks atthrottle body mounting area and intake
manifold
sealing surfaces.
• Ignition wires for cracking, hardness, proper
routing and carbon tracking.
• Wiring for proper connections, pinches and cuts.
• Fuel lines for being pinched or misrouted.

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.)

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.

6E2-92 DRIVEABILITY AND EMISSIONS
LACK OF POWER, SLUGGISH OR SPONGY
Definition: Engine delivers less than expected power.
Little or no increase in speed when
accelerator
pedal is pushed down part
way.
PRELIMINARY CHECKS
• Perform the careful visual/physical checks as
described at start of "Symptoms," Section "6E2-
B."
•
Compare customer's car to similar unit. Make sure
the
vehicle has an actual problem.
• Remove air filter and check air filter for dirt, or for
being plugged. Replace as necessary.
FUEL SYSTEM
• CHECK: Rescricted fuel filter.
• CHECK: Fuel pressure, use CHART A-7.
• CHECK: Contaminated fuel.
• CHECK: Fuel injectors are correct for the vehicle.
IGNITION SYSTEM
• CHECK: Ignition timing, using "Scan tool".
• CHECK: Knock sensor system for excessive spark
retard activity. Refer to CHART
C-5. Use
"Scan tool".
• CHECK: Secondary voltage using an oscilloscope
or a spark tester J 26792 (ST-125), or
equivalent, to check for a weak coil.
ADDITIONAL CHECKS
• CHECK: Engine control module grounds for being
clean,
tight and in their proper locations.
See engine control module wiring
diagrams.
• CHECK: Exhaust gas recirculation operation for
being open or partly open all the time.
- Refer to CHART
C-7.
• CHECK: Generator output voltage. Repair if less
than 9
or more than 16 volts.
• CHECK: Exhaust system for possible restriction.
Refer
to CHART B-1.
-Inspect exhaust system for damaged
or collapsed pipes.
-
Inspect muffler for heat damage or
possible internal failure.
• CHECK: Torque converter clutch for proper
operation. Refer
to AUTOMATIC
TRANSMISSION
(SECTION 7A).
ENGINE MECHANICAL
• CHECK: Engine valve timing and compression.
• CHECK: Engine for correct or worn camshaft.
Refer
to ENGINE MECHANICAL
DIAGNOSIS
(SECTION 6A).
DETONATION/SPARK KNOCK
Definition: A mild to severe ping, usually worse under
acceleration. The engine makes sharp
metallic knocks that change with throttle
opening.
Sounds like popcorn popping.
PRELIMINARY CHECKS
• Perform the careful visual/physical checks as
Low engine coolant.
Restricted air
flow to radiator, or restricted
water flow through radiator.
Correct engine
coolant solution should be a 50/
50 mix of anti-freeze engine coolant (or
equivalent) and water.
described at start
of "Symptoms," Section "6E2-FUEL SYSTEM
B."
•
Park/Neutral position switch. Be sure "Scan tool"
indicates drive with gear selector in drive or
overdrive. Use
CHART C-1A.
• If "Scan tool" readings are normal (see facing page
of on-board diagnostic system check) and there
are no engine mechanical faults,
fill fuel tank with a
gasoline
that has a minimum octane reading of 87
and revaluate vehicle performance.
• CHECK: Exhaust gas recirculation system for not
opening. Use CHART C-7.
COOLING SYSTEM
• Check for obvious overheating problems:
• NOTICE: To determine if the condition is caused by
a rich
or lean system, the car should be
driven at the speed
of the complaint.
Monitoring
LT. Fuel Trim will help
identify problem.
Lean-
LT. Fuel Trim above 142. Refer to
"Diagnostic Aids" on facing page of
diagnostic trouble code 44.
Rich-LT. Fuel Trim below 118. Refer to
"Diagnostic Aids" on facing page of
diagnostic trouble code 45.
• CHECK: Fuel pressure, use CHART A-7.
..

IGNITION SYSTEM
• CHECK: Spark plugs for proper heat cause. Refer
to Owner's Manual.
• CHECK: Ignition timing, using a "Scan tool".
ENGINE MECHANICAL
• CHECK: For excessive oil in the combustion
chamber. -
Valve oil seals for leaking.
• CHECK: Combustion chambers for excessive
carbon
build up. Remove carbon with top
engine cleaner and follow instructions on
can.
DRIVEABILITY AND EMISSIONS 6E2-93
• CHECK: Combustion chamber pressure by
performing a compression test.
See
ENGINE MECHANICAL DIAGNOSIS
(SECTION 6A).
• CHECK: For incorrect basic engine parts such as
cam, heads, pistons, etc.
HESITATION, SAG, STUMBLE
Definition: Momentary lack of response as the
accelerator is pushed down. Can occur at
all car speeds. Usually most severe when
first trying
to make the car move, as from a
stop sign. May cause engine to
stall if
severe enough.
PRELIMINARY CHECKS
• Perform the careful visual/physical checks as
described at start of "Symptoms," Section "6E2-
B."
SENSORS
• CHECK: Throttle position sensor for binding or
sticking. Voltage should increase at a
steady
rate as throttle is moved toward
Wide Open Throttle.
• CHECK: Manifold absolute pressure sensor-use
CHART C-10.
FUEL SYSTEM
• CHECK: Fuel pressure, use CHART A-7.
• CHECK: Fuel injectors are correct for vehicle.
• CHECK: Contaminated fuel.
• CHECK: Evaporative emission canister purge
system
for proper operation. Refer to
"Evaporative Emission Control System,"
Section "6E2-C3."
IGNITION SYSTEM
• CHECK: Spark plugs for being fouled, or for faulty
secondary wiring.
• CHECK: Ignition timing, using a "Scan tool".
• CHECK: Ignition system ground.
ADDITIONAL CHECKS
• CHECK: Exhaust gas recirculation operation, use
CHART
C-7.
• CHECK: Engine thermostat functioning correctly
and proper heat range.
• CHECK: Generator output voltage. Repair if less
than 9 or more than 16 volts.
CUTS OUT, MISSES
Definition: Steady pulsation or jerking that follows
engine speed, usually more pronounced
as engine load increases, not normally felt
above 1500 revolution per minute or 48
kph
(30 mile per hour). The exhaust has a
steady spitting sound at
idle or low speed.
PRELIMINARY CHECKS
• Perform the careful visual/physical checks as
described at start of "Symptoms," Section "6E2-
B."
IGNITION SYSTEM
• Check for cylinder miss by:
1. Start engine, allow engine to stabilize then
disconnect
idle air control motor. Remove
one spark
plug wire at a time, using insulated
pliers.
CAUTION: Do not perform this test for
more than 2 minutes,
as this test may
cause damage to the three
way
catalytic converter.
2. If there is a revolution per minute drop on all
cylinders (equal
to within 50 revolution per
minute), go
to "Rough, Unstable, or Incorrect
Idle, Stalling"
symptom. Reconnect idle air
control valve.