light ISUZU TROOPER 1995 Workshop Manual

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

DRIVEABILITV AND EMISSIONS 6E2-99
SECTION C
COMPONENTS SYSTEMS
CAUTION
When fasteners are removed, always reinstall them at the same location from which they were removed. If a
fastener needs
to be replaced, use the correct part number fastener for that application. If the correct part number
fastener is not available, a fastener of equal size and strength (or stronger) may be used. Fasteners that are not
reused, and those requiring thread locking compound will be called out. The correct torque value must be used
when installing fasteners that require it. If the above conditions are not followed, parts or system damage could
result.
Section
"C" provides information on the following:
• General description of components and sub-systems.
• On-vehicle service.
• Part names and group numbers.
• Diagnostic charts. These include a functional check of the system as well as diagnosis of any problem found in
the functional check.
For locations
of components, wiring diagrams, and engine control module terminal and view, refer to the front of
"Engine Components/Wiring Diagrams/Diagnostic Charts", Section "A".
Refer to the following sections for the appropriate sub-system information:
• C1 Engine Control Module (ECM) and Sensors ................................. Page 6E2-1 00
•
C2 Fuel Metering System .................................................. Page 6E2-116
• C3 Evaporative Emission (EVAP) Control System ............................... Page 6E2-134
• C4 Electronic Ignition (EI) System/Ignition Control (IC) ........................... Page 6E2-138
• C5 Knock Sensor (KS) System .............................................. Page 6E2-146
• C7 Exhaust Gas Recirculation (EGR) System ................................... Page 6E2-151
• C8 Shift Indicator Light (M/T Only) ........................................... Page 6E2-157
• C1 0 Air Conditioning (A/C) Compressor Clutch Control System ..................... Page 6E2-161
• C13 Positive Crankcase Ventilation (PCV) ....................................... Page 6E2-164
DIAGNOSTIC CHARTS
The following diagnostic charts can be found at the end of some of the sections.
• Chart C-1A Park/neutral Position (PNP) Switch Diagnosis (Auto Transmission only) .... Page 6E2-108
• Chart C-1 D Manifold Absolute Pressure (MAP) Output Check ...................... Page 6E2-11 0
•
Chart C-1 E Power Steering Pressure (PSP) Switch Diagnosis ...................... Page 6E2-112
• Chart C-1 F Heated Oxygen Sensor (H02S) Heater Check ......................... Page 6E2-114
• Chart C-2A Injector Balance Test ............................................. Page 6E2-128
• Chart C-2C Idle Air Control (lAC) System Check ................................. Page 6E2-130
• Chart C-2D Induction Air Control System Check (DOHC Only) ...................... Page 6E2-132
• Chart C-3 Evaporate Emission Canister Purge Valve Check ....................... Page 6E2-136
• Chart C-4D-1 Electronic Ignition (EI) Misfire at Idle ................................ Page 6E2-142
• Chart C-4D-2 Electronic Ignition (EI) Misfire Under Load ............................ Page 6E2-144
• Chart C-5 Knock Sensor (KS) System Check .................................. Page 6E2-148
• Chart C-7A Exhaust Gas Recirculation (EGR) System Check ....................... Page 6E2-154
• Chart C-8 Manual Transmission (MIT) Shift Light Check ......................... Page 6E2-158
• Chart C-1 0 Air Conditioning (A/C) System Functional Check ....................... Page 6E2-162

6E2-100 DRIVEABILITY AND EMISSIONS
SECTION C1
ENGINE CONTROL MODULE (ECM) & SENSORS
CONTENTS
General Description ...................... 6E2-1 00
Engine Control Module (ECM) .............. 6E2-100
Engine Control Module (ECM) Function ....... 6E2-1 00
Information Sensors ..................... 6E2-1 01
Engine Coolant Temperature (ECT) Sensor ... 6E2-101
Intake Air Temperature (IAT) Sensor ........ 6E2-101
Heated Oxygen Sensor (H02S) ........... 6E2-101
Throttle Position
(TP) Sensor ............. 6E2-102
Manifold Absolute Pressure (MAP) Sensor ... 6E2-102
Vehicle Speed Sensor (VSS) ............. 6E2-102
Knock Sensor (KS) (DOHC ONLY) .......... 6E2-102
Air Conditioning (A/C) Request Signal ...... 6E2-1 02
Power Steering Pressure (PSP) Switch ...... 6E2-1 02
Park/Neutral Position (PNP) Switch
(Auto only)
........................ 6E2-1 03 Diagnosis ............................. 6E2-1 03
Engine Control Module (ECM) .............. 6E2-1 03
Electrically Erasable Programmable Read
Only Memory ........................ 6E2-1 03
Engine Control Module (ECM) Inputs ....... 6E2-103
Engine Coolant Temperature (ECT) Sensor ... 6E2-1 04
Intake Air Temperature (IAT) Sensor ........ 6E2-1 04
Heated Oxygen Sensor
(H02S) ........... 6E2-1 04
Throttle Position
(TP) Sensor ............. 6E2-1 04
Manifold Absolute Pressure (MAP) Sensor
... 6E2-1 04
Vehicle Speed Sensor (VSS) ............. 6E2-1 04
Air Conditioning (A/C) Request Signal
Power Steering Pressure
(PSP) Switch ..... .
Crankshaft Position
(CKP) Reference Signal ..
Park/Neutral Position (PNP) Switch ....... .
Knock Sensor
(KS) ................... .
On-Vehicle Service ..................... .
Engine Control Module
(ECM) ............ .
Engine Control Module
(ECM) Replacement ..
Engine Coolant Temperature (ECT) Sensor ... .
Intake Air Temperature (IAT) Sensor ........ .
Heated Oxygen Sensor
(H02S) ............ .
Throttle Position
(TP) Sensor ............. .
Manifold Absolute Pressure (MAP) Sensor
.... .
Vehicle Speed Sensor
(VSS) ............. .
Power Steering Pressure
(PSP) Switch ...... .
Park/Neutral Position
(PNP) Switch ......... .
Chart C-1A Park/Neutral Position
(PNP)
Switch Diagnosis .................... .
Chart
C-1 D Manifold Absolute Pressure (MAP)
Output Check
...................... .
Chart
C-1 E Power Steering Pressure (PSP)
Switch Diagnosis .................... .
Chart
C-1 F Heated Oxygen Sensor (H02S)
Heater Check ....................... .
6E2-104
6E2-104
6E2-104
6E2-104
6E2-104
6E2-104
6E2-104
6E2-105
6E2-105
6E2-106
6E2-106
6E2-107
6E2-107
6E2-107
6E2-107
6E2-107
6E2-108
6E2-110
6E2-112
6E2-114
GENERAL DESCRIPTION
ENGINE CONTROL MODULE (ECM)
The Engine Control Module (ECM) (Fig. 6E2-50),
located under the instrument panel, is the control
center of the fuel injection system. If constantly looks
at the information from various sensors, and controls
the systems that affect vehicle performance. The ECM
also performs the diagnostic function of the system. It
can recognize operational problems, alert the driver
through the "Check Engine" malfunction indicator
lamp, and store a diagnostic trouble code or diagnostic
trouble codes which identify the problem areas to aid
the technician in making repairs.
See "Introduction"
Section "6E2" for more information on using the
diagnostic function
of the ECM.
For service, this ECM is replaced as a complete unit.
There are no serviceable parts in the
ECM. The
calibrations are stored in the
ECM in the Electronic
Erasable Programmable Read Only Memory
(EEPROM).
ENGINE CONTROL MODULE (ECM)
FUNCTION
This ECM supplies either 5 to 12 volts to power various
sensors
or switches. This is done through resistances
in the
ECM which are so high in value that a test light
Fig. 6E2-50

will not light when connected to the circuit. In some
cases, even an ordinary shop voltmeter
will not give an
accurate reading because its resistance is
too low.
Therefore, a 10 megohms input impedance digital
voltmeter is required to assure accurate voltage
readings.
The Engine
Control Module (ECM) controls output
circuits such as the fuel injectors, idle air control valve,
air conditioning clutch relay, etc. by controlling the
ground circuit through transistors
or a device called a
"quad-driver".
INFORMATION SENSORS
Engine Coolant Temperature (ECT) Sensor
(Fig. 6E2-51)
The Engine Coolant Temperature (ECT) Sensor is a
thermistor
(a resistor which changes value based on
temperature) mounted in the engine coolant stream.
Low ECT produces a high resistance (1 00,000 ohms at
-40.C/-40.F) while high temperature causes low
resistance (70 ohms at 130.C/266.F).
The ECM supplies a 5-volts signal to the ECT sensor
through a resistor in the
ECM and measures the
voltage. The voltage
will be high when the engine is
cold, and low when the engine is hot.
By measuring the voltage, the
ECM knows the ETC.
ECT affects most systems the ECM controls.
A failure in the
ECT sensor circuit should set a
Diagnostic Trouble Code
(DTC) 14. Remember, these
DTC(s) indicate a failure in the
ETC circuit, so proper
use
of the chart will lead to either repairing a wiring
problem or replacing the sensor, to properly repair a
problem.
1. Engine coolant temperature sensor
2. Harness connector to ECM
3. Locking tab
Fig. 6E2-51
Intake Air Temperature (IAT) Sensor
The Intake Air Temperature (IAT) sensor is a
thermistor, a resistor which changes
value based on
the temperature
of air entering the engine. Low
temperature produces a high resistance
(1 00,000
ohms at -4o·c/-40.F), while high temperature causes
low resistance (70 ohms at 130.C/266.F).
The ECM supplies a 5-volts signal to the sensor through
a resistor in the
ECM and measures the voltage. The
voltage
will be high when the intake air is cold, and low
DRIVEABILITV AND EMISSIONS 6E2-1 01
when the air is hot. By measuring the voltage, the ECM
knows the lAT.
The IAT sensor is also used to control spark timing and
delays exhaust gas recirculation when intake air is
cold.
A failure in the IAT sensor circuit should set a DTC 23.
Heated Oxygen Sensor (H02S) (Fig. 6E2-52)
The Heated Oxygen Sensor (H02S) is mounted in the
exhaust system where
it can monitor the Oxygen (02)
content of the exhaust gas stream. The 02 content in
the exhaust reacts
with the sensor to produce a voltage
output. This voltage ranges
from approximately .1 volt
(high 02-lean mixture) to .9 volt (low 02-rich mixture).
This voltage can
be measured with a digital voltmeter
having at
least 10 megohms input impedance. Use of
standard shop type voltmeters will result in very
inaccurate readings.
By monitoring the voltage
output ofthe H02S, the ECM
will know what fuel mixture command to give to the
injector
(lean mixture-low 02 voltage= rich command,
rich mixture-high
02 voltage= lean command).
The
H02S circuit, if open, should set a DTC 13. A
constant
low voltage in the sensor circuit should set a
DTC 44. While a constant high voltage in the circuit
should set a DTC 45. DTC(s) 44 and 45 could also be set
as a result of fuel system problems. See DTC charts for
conditions that can cause a lean or rich system.
The
H02S works in the same manner as the non-H02S
The exception is that battery positive voltage is
supplied to a heating unit that is part of the sensor
itself. This heater receives voltage
from the ECM's
main
relay circuit.
The heater
helps to heat up the H02S so the ECM can
start
controlling the fuel injection sooner for better fuel
emissions. There are no malfunction DTC(s) to detect if
the heater part of the sensor is working. To check the
heater, refer to "Functional
Check" in this section.
Fig. 6E2-52
~
\W

Park/Neutral Position (PNP) Switch (Auto Only)
The Park/Neutral position (PNP) switch indicates to the
Engine Control Module
(ECM) when the transmission
is in park, neutral
or drive. This information is used for
the exhaust gas recirculation, and the idle air control
valve operation.
NOTE:
• Vehicle
should not be driven with PNP switch
disconnected,
as idle quality will be affected and a
possible false diagnostic trouble code
(DTC) 24
(vehicle speed sensor).
DRIVEABILITY AND EMISSIONS 6E2-103
See DIAGNOSIS AND GENERAL SERVICE Section for
more information on the PNP switch. The PNP switch is
part
of the neutral/start and backup light switch
assembly mounted on the transmission.
See CHART C-
1 A for PNP switch check.
DIAGNOSIS
To read the DTC(s), use a "Scan tool" or ground the
diagnostic test terminal,
with the engine not running
and the ignition
"ON". The "Check Engine" malfunction
indicator lamp
will flash DTC 12 three times and then
flash each
DTC stored in memory three times. All
DTC(s) stored in memory will have been read when
DTC 12 is flashed again.
No new
DTC(s) can be stored when in the diagnostics
test mode (diagnostics lead grounded). This
eliminates confusion while the system is being
serviced.
To clear the
DTC(s) from memory:
• Ignition "OFF".
•
Disconnect main fuse located in the under hood
fuse/relay center near the battery.
Since the ECM can have a failure which may affect only
one circuit, following the diagnostic procedures in this
section
will determine which circuit has a problem and
where
it is.
If a diagnostic chart indicates thatthe ECM connections
or ECM is the cause of a problem, and the ECM is
replaced,
but does not correct the problem, one of the
following may be the reason.
• There is a problem with the ECM terminal
connections-The diagnostic chart will say ECM
connections or ECM. The terminals may have to
be removed from the connector in order to check
them properly.
• The ECM is not correct for the Vehicle-Ane
incorrect
ECM may cause a malfunction and may
set a DTC.
• The problem is intermittent -This means that
the problem is
not present at the time the system is
being checked.
In this case, refer to the
"Symptoms" portion of the manual and make a
careful physical inspection
of all portions of the
system involved.
• Shorted solenoid, relay coil, or harness
Solenoid and relays are turned "ON" and "OFF" by
the
ECM, using internal electronic switches called
"drivers".
Each driver is part of a group of four,
called "quad-drivers". Failure of one driver can
damage any other driver in the set. A
shorted solenoid, relay coil, or harness in a l-EFT­
SHCI
computer will not damage the ECM, but will
cause the circuit and controlled component to be
inoperative. When the circuit fault is not present or
has been repaired, the "quad-driver" will again
operate in a normal manner due to its fault
protected design. If a fault has been repaired in a
circuit controlled by a "quad-driver", the original
ECM should be reinstalled and the circuit checked
for proper operation. ECM replacement will not be
necessary if the repaired circuit or component now
operates correctly.
J 34636 or BT-8405 testers or equivalent provide a fast,
accurate means
of checking for a shorted coil or a short
to battery positive voltage.
• The replacement ECM may be faulty-After the
ECM is replaced, the system should be re-checked
for proper operation. If the diagnostic chart again
indicates the
ECM is the problem, substitute a
known good
ECM. Although this is a rare
condition,
it could happen.
ENGINE CONTROL MODULE (ECM)
A faulty ECM will be determined in the diagnostic
charts.
ELECTRONICALL V ERASABLE
PROGRAMMABLE READ
ONL V MEMORY
A faulty electrically erasable programmable read only
memory, which is part of the ECM, will set a DTC 51.
ENGINE CONTROL MODULE (ECM)
INPUTS
All of the sensors and input switches can be diagnosed
by the use
of "Scan tool".
Following is a short description of how the sensors and
switches can be diagnosed by the use
"Scan tool". The
"Scan tool" can also be used to compare the values for
a normal running engine with the engine you're
diagnosing.

DRIVEABILITY AND EMISSIONS 6E2-1 09
CHART C-1A
PARK/NEUTRAL POSITION (PNP) SWITCH DIAGNOSIS
(AUTO TRANSMISSION ONLY)
CD • IGNITION "ON" ENGINE NOT RUNNING.
• "SCAN TOOL" INSTALLED.
"SCAN TOOL" SHOULD DISPLAY "PARK/NEUTRAL" POSITION
(PNP} WITH TRANSMISSION
IN PARK OR NEUTRAL?
AND "R·D-L" WITH TRANSMISSION IN ALL OTHER SHIFT
POSITIONS?
DOES
IT?
@ • REMOVE THE DIODE FROM THE UNDERHOOD FUSE/RELAY CENTER. • USE A DVM PROBE THE BLU/PINK WIRE.
SHOULD HAVE 12 VOLTS.
DOES IT?
• TEST LIGHT CONNECTED TO BATTERY POSITIVE SENSOR,
PROBE THE PNK/BLU WIRE AT THE DIODE CAVITY.
• TEST LIGHT SHOULD BE "ON" WITH TRANSMISSION IN PARK.
IS IT?
OPEN IN BLU/PNK WIRE OR FAULTY ENGINE CONTROL
MODULE.
OPEN
IN PNK/BLU WIRE OR MISADJUSTED PNP SWITCH OR FAULTY PNP SWITCH.

DRIVEABILITY AND EMISSIONS 6E2-115
CHART C-1F
HEATED OXYGEN SENSOR (H02S) HEATER CHECK
CD • IGNITION "OFF"
• DISCONNECT FOUR PIN CONNECTOR TO HEATED OXYGEN SENSOR (H02S).
• IGNITION "ON" ENGINE NOT RUNNING • USING DVOM PROBE WHT /BLU WIRE OF FOUR PIN CONNECTOR
• SHOULD HAVE BATTERY POSITIVE VOLTAGE
DOES IT?
@ • IGNITION "ON" ENGINE RUNNING
• USING A TEST LIGHT TO BATTERY POSITIVE
VOLTAGE PROBE BLK WIRE OFF FOUR PIN CONNECTOR
• LIGHT SHOULD BE "ON" IS IT?
@ • USING DVOM MEASURE RESISTANCE AT THE H02S BETWEEN BLK WIRE AND WHT/RED WIRE THAT BECOMES THE BLK/YEL WIRE AFTER THE FOUR PIN CONNECTOR
• SHOULD HAVE 3.5 TO 14.3 OHMS
RESISTANCE (RESISTANCE VARIES WITH
TEMPERATURE) DOES IT?
OPEN IN BLK/YEL OR RED/GRN WIRE
CLEAR DIAGNOSTIC TROUBLE CODES AND CONFIRM "CLOSED LOOP" OPERATION AND NORMAL "CHECK ENGINE" MALFUNCTION
INDICATOR LAMP OPERATION.

1~1 Measure (If Installing a New Idle Air
Control (lAC) Valve) (Fig. 6E2-82)
• Distance between tip of idle air control (lAC)
valve pintle and mounting flange.
-
If greater than 28 mm, finger pressure to
slowly retract the pintle. The force required
to retract the pintle
of a new valve will not
cause damage to the valve.
Fig. 6E2-82
E) INSTALLATION
3. lAC valve assembly
2. lAC valve attaching screw
1. lAC valve electrical connector
MINIMUM THROTTLE BODY (TB)
POSITION CHECK
The minimum throttle body (TB) position (throttle stop
screw) adjustment
for the 3.2L should not be
considered the
"minimum idle speed", as on other fuel
injected engines. Low internal friction and provision
for slight production variations and various operation
altitudes resulted in a calibrated
minimum TB position
which is too
low to allow most engines to idle. The
adjustment is preset at the factory and no further
adjustment should be necessary.
If there is a complaint of high idle speed, vacuum leaks
should be considered the
most likely cause. Because
the Engine
Control Module (ECM) "learns" Idle lAC, it is
even less likely
that a stalling complaint would be due
to
an incorrect minimum TB position. In either case,
the
"Symptoms," Section "6E2-B" and lAC valve check
CHART C-2C should be referred to.
If it is determined that the minimum TB position is
suspect,
be sure lAC valve is not "lost'' (not actually at
the location indicated by current
lAC "counts"). The
lAC valve could be "lost" if ECM power has been
interrupted
with the ignition "ON", or the lAC valve has
been disconnected
with the engine running since the
last reset,
as described previously in this section in the
"lAC Valve Assembly" general description.
DRIVEABILITY AND EMISSIONS 6E2-127
The minimum TB position may be checked using the
following procedure.
1. Block drive wheels, and apply parking brake.
2. Connect "Scan tool" to the data link connector.
3. Start engine and allow to reach operating
temperature (about
go•q and "Closed Loop".
4. A/T-shift to DRIVE ("D") and then back to neutral
("N").
5. Select power steering pressure switch input on
"Scan tool". With air conditioning and all electrical
accessories
"OFF", transmission in natural, "Scan
tool" should read "OFF" or "NORMAL". (If not,
refer to
CHART C-1 E to diagnose and repair faulty
power steering pressure switch circuit before
proceeding).
Allow idle to stabilize.
6. Select lAC valve display on "Scan tool", and read
lAC valve counts. If between 5-45 counts, the
minimum
TB position adjustment is acceptable. It
is important to allow idle speed to stabilize to
assure correct counts are determined.
If counts in step 6 are too low, check for intake air
(vacuum) leaks at hoses,
TB and intake manifold or
damaged throttle lever and correct as necessary.
Also, refer to
CHART C-2C facing page "Diagnostic
Aids". If no vacuum leaks or other cause of
excessive air into the intake are found, it may be
necessary
to replace the TB to correct the low idle
speed problem. Refer to
"TB Replacement" in this
section.
If counts in Step 6 are too high, check for damaged
throttle lever or airflow restriction by the
TB. If no
problem is evident, remove inlet air
duct at the TB,
and
clean residue from inside of TB bore and from
edges of TB using carburetor cleaner and a shop
towel. (Do Not use a cleaner that contains methyl
ethyl ketone.
It is an extremely strong solvent, and
not necessary for this type of deposit). Re-check
"Scan tool" lAC valve counts, per the preceding
procedure.
If counts are still too high it may be necessary to
replace the
lAC valve or the TB assembly, If no
vacuum leaks are indicated
or engine loads are
present.
Minimum Throttle Body (TB) Position
(Non-Adjustable)
\fl CAUTION:
VI • It is extremely unlikely that this adjustment will
ever be necessary on a TB that has not been
tampered
with after production! If idle
revolution per minute is low, you may need
to
replace the TB to correct the low idle speed.

6E2-128 DRIVEABILITY AND EMISSIONS
CHART C-2A
INJECTOR BALANCE TEST
The injector balance tester is a tool used to turn the injector on for a precise amount of time, thus spraying a
measured
amount of fuel into the manifold. This causes a drop in fuel rail pressure that we can record and
compare between each injector.
All injectors should have the same amount of pressure drop (± 10 kPa). Any
injector with a pressure drop that is 10 kPa (or more) greater or less than the average drop of the other injectors
should be considered faulty and replaced.
NOTE: It will be necessary to remove the intake plenum to perform this procedure. Refer to intake plenum
remove procedure in this section. It will also be necessary to install the Intake Manifold Diagnostic Plate J
39185 to enable the engine to be run with the plenum removed. Refer to Chart A-8 in Section "6E2-A" of
this service manual.
STEP 1
Engine "cool down" period (10 minutes) is necessary to avoid irregular readings due to "Hot Soak" fuel boiling.
With ignition "OFF" connect fuel gauge J 347301 or equivalent to fuel pressure tap. Wrap a shop towel around
fitting
while connecting gage to avoid fuel spillage. Refer to Chart A-7 in Section 6E2-A, Page 1 of 3.
Disconnect harness connectors at all injectors, and connect injector tester J 34730-3, or equivalent, to one injector.
Follow manufacturers instructions for use of adaptor harness. Ignition must be "OFF" at least 10 seconds to
complete engine control module shutdown cycle. Fuel pump should run about 2 seconds after ignition is turned
"ON". At this point, insert clear tubing attached to vent valve into a operation. Repeat this step until all air is bled
from gauge.
STEP 2
Turn ignition "OFF" for 10 seconds and then "ON" again to get fuel pressure to its maximum. Record this initial
pressure reading. Energize tester one time and note pressure drop at its lowest point (Disregard any slight
pressure increase after drop hits low point). By subtracting this second pressure reading from the initial pressure, ~
we have the actual amount of injector pressure drop.
STEP 3
Repeat step 2 on each injector and compare the amount of drop. Usually, good injectors will have virtually the
same drop. Retest any injector
that has a pressure difference of 10 kPa, either more or less than the average of the
other injectors on the engine.
Replace any injector that also fails the retest. If the pressure drop of all injectors is
within 10 kPa of this average, the injectors appear to be following properly.
Reconnect them and review "Symptoms", Section "6E3-B".
NOTE: The entire test should NOT be repeated more than once without running the engine to prevent flooding.
(This includes any retest on faulty injectors). To run the engine with the intake plenum removed use the
Intake Manifold Diagnostic Plate.
•

6E2-130 DRIVEABILITY AND EMISSIONS
CHART C-2C
IDLE AIR CONTROL (lAC) SYSTEM CHECK
Circuit Description:
The engine control module (ECM) controls engine idle speed with idler air control (lAC) valve. To increase idle
speed, the ECM retracts the lAC valve pintle away from its seat, allowing more air to bypass the throttle bore. To
decrease
idle speed, it extends the lAC valve pintle towards its seat, reducing bypass air flow. A "Scan tool" will
read the ECM commands to the lAC valve in counts. Higher counts indicate more air bypass (higher idle). Lower
counts indicate
less air is allowed to bypass (lower idle).
Test Description:
Number below re{er to circled numbers on the diagnostic chart.
1. The lAC tester is used to extend and retract the lAC valve. Valve movement is verified by an engine speed
change.
If no change in engine speed occurs, the valve can be retested when removed from the throttle body.
2. This step checks the quality of the lAC movement in step 1. Between 700 revolution per minute (rpm) and
about
1500 rpm, the engine speed should change smoothly with each flash of the tester light in both extend
and retract.
If the lAC valve is retracted beyond the control range (about 1500 rpm), it may take many flashes
in the extend position before engine speed will begin to drop. This is normal on certain engines, fully
extending lAC may cause engine stall. This may be normal.
3. Steps 1 and 2 verified proper lAC valve operation. This step checks the lAC circuits. Each lamp on the node
light should flash red and green while the lAC valve is cycled. While the sequence of color is not important if
either light "OFF" or does not flash red and green, check the circuits for faults, beginning with poor terminal
contacts.
Diagnostic Aids:
A slow, unstable, or fast idle may be caused by a non-lAC system problem that cannot overcome by the lAC valve.
Out
of control range lAC "Scan tool" counts will be above 60 if idle is too low, and zero counts if idle is too high. The ..-...
following checks should be made to repair a non-lAC system problem. _......._
• Vacuum Leak (High Idle)
If idle
is too high, stop the engine. Fully extend (low) lAC with tester.
Start engine.
If idle speed is above 800 rpm, locate and correct vacuum leak including PCV system. Also check
for binding of throttle blade or linkage.
•
Lean heated oxygen sensor signal (High Air/Fuel Ratio)
The
idle speed may be too high or too low. Engine speed may vary up and down and disconnecting the lAC
valve
does not help. Diagnostic trouble code 44 may be set. "Scan tool" oxygen (02) voltage will be less than
100 mV (.1 volt). Check for low regulated fuel pressure, water in fuel, or a restricted injector.
• Rich heated oxygen sensor signal (Low Air/Fuel Ratio)
The
idle speed will be too low. "Scan tool" lAC counts will usually be above 80. System is obviously rich and
may exhibit
black smoke in exhaust.
"Scan tool" 02 voltage will be fixed about 750 mV (.75 volt).
Check
for high fuel pressure, leaking or sticking injector. Silicon contaminated heated oxygen sensor will
"Scan
tool" an 02 voltage slow to respond.
• Throttle Body
Remove
lAC valve and inspect bore for foreign material.
• lAC Valve
Electrical Connections
lAC valve
connections should be carefully checked for proper contact.
• PCV Valve
An incorrect or faulty PCV valve may result in an incorrect idle speed.
• Refer to "Rough, Unstable, Incorrect Idle or Stalling" in "Symptoms," Section "6E2-B".
• If
intermittent poor driveability or idle symptoms are resolved by disconnecting the lAC, carefully recheck
connections,
valve terminal resistance, or replace lAC.