MITSUBISHI MONTERO 1991 Service Manual

mechanism. Testing information is not available from manufacturer. See
appropriate wiring diagram in L - WIRING DIAGRAMS article in the
ENGINE PERFORMANCE Section.
INTAKE AIR TEMPERATURE SENSOR
1) Sensor is incorporated in airflow sensor assembly inside
air filter housing. Disconnect airflow sensor connector. See Fig. 1.
Fig. 1: Airflow Sensor Connector Terminal ID
Courtesy of Mitsubishi Motor Sales of America.
2) Measure resistance between terminals No. 4 and 6 of
airflow sensor connector (sensor side of connector). For
specifications, see INTAKE AIR TEMPERATURE SENSOR RESISTANCE table.
Replace airflow sensor assembly if air temperature sensor resistance
is not within specification.

INTAKE AIR TEMP SENSOR RESISTANCE TABLE








\









\









\









\




TemperatureF (C) Ohms
All Models
32 (0) ........................ 6000
68 (20) ....................... 2700
176 (80) ....................... 400









\









\









\









\




MOTOR POSITION SENSOR
NOTE: Some engines are not equipped with Motor Position Sensor
(MPS). MPS may be a separate unit mounted to throttle body
or it may be incorporated in ISC motor assembly, depending
upon vehicle application.
Pickup 2.4L & Ram-50 2.4L
1) Disconnect MPS connector. See Fig. 2. Connect ohmmeter
lead to ground. Connect other ohmmeter lead to terminal No. 3 of
sensor connector. If continuity is not present, repair wiring harness
as necessary. If continuity is present, go to next step.
Fig. 2: Motor Pos. Sensor Connector Term. ID
Courtesy of Mitsubishi Motor Sales of America.
2) Connect ohmmeter leads to terminals No. 2 and 3.
Resistance should be 4000-6000 ohms. If resistance is not within

specified range, replace MPS.
CAUTION: DO NOT apply more than 6 volts to ISC motor.
3) Operate ISC motor by connecting a 6-volt source directly
to appropriate terminals of ISC motor connector. For ISC motor
operation test procedures, see IDLE SPEED CONTROL (ISC) MOTOR
OPERATION TEST under IDLE CONTROL SYSTEM.
4) While operating ISC motor, measure resistance between MPS
connector terminals No. 3 and 5. Observe ohmmeter during ISC motor
operation. If MPS resistance does not vary within a 4000-6000 ohm
range or if resistance does not change smoothly, replace MPS (vehicles
equipped with separate MPS) or ISC motor assembly (vehicles equipped
with MPS incorporated in ISC).
OXYGEN SENSOR
1-Wire Or 2-Wire
1) On all models, warm engine until coolant temperature is
185-205
F (85-96C). Disconnect oxygen sensor connector. See Fig. 3 or
4.
2) Connect digital voltmeter between terminal No. 1 and
ground. Repeatedly race engine and observe oxygen sensor output
voltage. If output is not 0.6-1.0 volt, replace oxygen sensor.
Fig. 3: O2 Sensor Connector Terminal ID (1 Wire)
Courtesy of Mitsubishi Motor Sales of America.

Fig. 4: O2 Sensor Connector Terminal ID (2 Wire)
Courtesy of Mitsubishi Motor Sales of America.
4-Wire Heated
1) Warm engine until coolant temperature is 185-205
F (85-

95C). Disconnect oxygen sensor connector. See Fig. 5. Connect
ohmmeter between heater terminals of oxygen sensor connector as
specified in OXYGEN SENSOR 4-WIRE CONNECTOR TERMINAL IDENTIFICATION
table. This test checks resistance of oxygen sensor heater element.
Fig. 5: O2 Sensor Connector Term. ID
Courtesy of Mitsubishi Motor Sales of America.
2) When oxygen sensor is at 68
F (20C), resistance should be
approximately 12 ohms (20 ohms on 3.0L models). If resistance is not
within specification, replace oxygen sensor.
CAUTION: DO NOT apply battery voltage to oxygen sensor output
terminals. Damage to oxygen sensor could result.
3) Apply battery voltage to oxygen sensor heater terminals as
specified in OXYGEN SENSOR 4-WIRE CONNECTOR TERMINAL IDENTIFICATION
table. This heats oxygen sensor heater element.
4) Connect digital voltmeter between output terminals
specified in OXYGEN SENSOR 4-WIRE CONNECTOR TERMINAL IDENTIFICATION
table. Repeatedly race engine and observe oxygen sensor output
voltage. If oxygen sensor output voltage is not within 0.6-1.0 volt,
replace oxygen sensor.
OXYGEN SENSOR 4-WIRE CONNECTOR TERMINAL ID TABLE









\









\









\









\









\









\









\







Heater Output

Circuit Circuit
Application Terminals Terminals
Montero, Pickup 3.0L & Ram-50 3.0L ..... 2 & 4 ............. 1 & 3









\









\









\









\









\









\









\







POWER STEERING OIL PRESSURE SWITCH
1) Power steering oil pressure switch is mounted on power
steering pump. Disconnect single wire connector at switch. Start
engine.
2) Connect ohmmeter between switch terminal and ground. If
continuity is present with steering wheel in straight-ahead position,
replace switch. If continuity is not present while turning steering
wheel, perform POWER STEERING IDLE-UP SYSTEM TEST. See IDLE-UP SYSTEMS
under IDLE CONTROL SYSTEM.
THROTTLE POSITION SENSOR
1) TPS is mounted to throttle body, at end of throttle shaft.
Disconnect TPS connector. See Fig. 6. Using ohmmeter, measure total
resistance between TPS connector terminals as specified in TPS
CONNECTOR TERMINAL IDENTIFICATION table. If resistance is not 3500-
6500 ohms, replace TPS.
2) Using an analog (needle-type) ohmmeter, measure variable
resistance between TPS connector terminals as specified in TPS
CONNECTOR TERMINAL IDENTIFICATION table.
3) Operate throttle valve from closed to wide open throttle.
If rate of resistance does not change smoothly within 3500-6500 ohms
throughout range of throttle valve movement, replace TPS.
Fig. 6: TPS Sensor Connector Terminal ID
Courtesy of Mitsubishi Motor Sales of America.
TPS CONNECTOR TERMINAL IDENTIFICATION TABLE









\









\









\









\

Terminal
Application Numbers
Total Resistance .................... 1 & 4
Variable Resistance
Montero, Pickup 3.0L,
& Ram-50 3.0L .................... 1 & 3
All Others ........................ 2 & 4









\









\









\









\









VEHICLE SPEED SENSOR
1) Vehicle Speed Sensor (VSS) is located in speedometer
assembly. Connect an ohmmeter between sensor terminals on back of
instrument panel. See Fig. 7 or 8.
2) Rotate speedometer cable. For each revolution of
speedometer cable, sensor should make and break continuity 4 times. If
ohmmeter reading does not fluctuate between continuity and no
continuity or if sensor does not make and break continuity 4 times for
each revolution, replace sensor.
Fig. 7: VSS Sensor Connector Term. ID (Montero)
Courtesy of Mitsubishi Motor Sales of America.
Fig. 8: VSS Sensor Connector Term. ID (P/U & Ram 50)
Courtesy of Mitsubishi Motor Sales of America.
MOTORS, RELAYS & SOLENOIDS

MOTORS
ISC Motor
See IDLE CONTROL SYSTEM.
RELAYS
NOTE: For internal wiring diagram of MPI control relay, see
appropriate L - WIRING DIAGRAMS article in the ENGINE
PERFORMANCE Section.
MPI Control Relay (Montero, Pickup 3.0L & Ram-50 3.0L)
1) MPI control relay is located near right kick panel. Check
for battery voltage at terminal No. 10 of relay connector. See Fig. 9.
If battery voltage is present, go to step 3). If battery voltage is
not present, check circuit between relay and battery, including
fusible link No. 1.
Fig. 9: MPI Control Relay Connector Term. ID (10 Pin)
Courtesy of Mitsubishi Motor Sales of America.
2) Apply battery voltage to terminal No. 10. Battery voltage
should not be present at terminals No. 4 and 5. Apply battery voltage
to terminal No. 10, and ground terminal No. 8. Battery voltage should
now be present at terminals No. 4 and 5.
3) Apply battery voltage to terminal No. 3. Battery voltage
should not be present at terminal No. 2. Apply battery voltage to
terminal No. 3, and ground terminal No. 7. Battery voltage should now
be present at terminal No. 2.
4) Apply battery voltage to terminal No. 9. Battery voltage
should not be present at terminal No. 2. Apply battery voltage to
terminal No. 9, and ground terminal No. 6. Battery voltage should now
be present at terminal No. 2. Replace relay if it does not test as
specified.
MPI Control Relay (Pickup 2.4L & Ram-50)
1) MPI control relay is located near right kick panel. Check
for battery voltage at terminal No. 4 of relay connector. See Fig. 10.
If battery voltage is present, go to step 3). If battery voltage is

not present, check circuit between relay and battery, including
fusible link No. 1.
Fig. 10: MPI Control Relay Connector Term. ID (8 Pin)
Courtesy of Mitsubishi Motor Sales of America.
2) Disconnect wiring harness connector at relay. Remove
relay. Check continuity between terminals No. 1 and 4, terminals No. 2
and 4 and terminals No. 3 and 4. If there is no continuity, go to next

step. If there is continuity, replace relay.
3) Check diode operation between terminals No. 6 and 8. If
there is continuity in only one direction, go to next step. If there
is no continuity in either direction or if there is continuity in both
directions, replace relay.
4) Measure resistance between terminals No. 6 and 7. If
resistance is approximately 35 ohms, go to next step. If resistance is
not approximately 35 ohms, replace relay.
5) Measure resistance between terminals No. 2 and 5 and
between terminals No. 3 and 5. In both tests, if resistance is
approximately 95 ohms, go to next step. If resistance is not
approximately 95 ohms, replace relay.
6) Connect positive lead of 12-volt source to terminal No. 7
and negative lead to terminal No. 6. If there is continuity between
terminals No. 1 and 4, go to next step. If there is no continuity,
replace relay.
7) Connect positive lead of 12-volt source to terminal No. 5
and negative lead to terminal No. 2. If there is continuity between
terminals No. 1 and 4, go to next step. If there is no continuity,
replace relay.
8) Connect positive lead of 12-volt source to terminal No. 5
and negative lead to terminal No. 3. If there is continuity between
terminals No. 1 and 4, go to next step. If there is no continuity,
replace relay.
9) Connect positive lead of 12-volt source to terminal No. 8
and negative lead to terminal No. 6. If there is continuity between
terminals No. 3 and 4 and between terminals No. 2 and 4, relay is
okay. If there is no continuity, replace relay.
SOLENOIDS
Fuel Pressure Control Solenoid Valve
See FUEL DELIVERY under FUEL SYSTEM.
Fuel Injector Solenoids
See FUEL CONTROL under FUEL SYSTEM.
FUEL SYSTEM
FUEL DELIVERY
NOTE: For fuel system pressure testing, see F - BASIC TESTING
article in the ENGINE PERFORMANCE Section.
FUEL CONTROL
Fuel Injectors
1) Using a stethoscope, check operating sound of injector(s)\
during engine cranking or idling. If clicking sound is heard,
injectors are okay. If clicking sound is not heard at each injector,
go to step 2).
2) Disconnect injector electrical connector. Measure
resistance between injector connector terminals. At 68
F (20C), if
resistance is not 13-16 ohms, replace injector.
3) If resistance is within specification, check injector
wiring circuit for open or short to ground. If wiring circuit tests
okay, replace injector.
IDLE CONTROL SYSTEM
NOTE: ISC motor adjusts throttle plate angle to regulate idle air