1991 MITSUBISHI MONTERO engine

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









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Heater Output

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









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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









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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

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

assembly.
IDLE-UP SYSTEMS
Power Steering Idle-Up System Test
1) Disconnect pressure hose from power steering pump. Connect
in-line a pressure gauge and hoses capable of handling 300 psi (21
kg/cm
). Also connect a shut-off valve in-line with pressure gauge.
See Fig. 13 .
Fig. 13: Connecting Pressure Gauge Shutoff Valve Assembly
Courtesy of Mitsubishi Motor Sales of America.
2) Bleed air from system by disabling ignition system and
cranking engine while turning steering wheel completely from left to

right several times. Start engine, and turn steering wheel back and
forth to raise fluid temperature to approximately 122-140F (50-60C).
3) With engine idling, gradually close shutoff valve of
pressure gauge to increase hydraulic pressure. If idle speed does not
increase 200-250 RPM when fluid pressure reaches 213-284 psi (15-20
kg/cm
), replace power steering idle-up switch.
4) Gradually open shutoff valve. If engine speed does not
return to curb idle speed between 100-142 psi (7-10 kg/cm
), replace
power steering idle-up switch. Remove testing equipment. Bleed air
from system as in step 2).
IGNITION SYSTEM
NOTE: For basic ignition checks, see F - BASIC TESTING article in
ENGINE PERFORMANCE Section.
TIMING CONTROL SYSTEMS
Crank Angle Sensor
Crank angle sensor is located inside distributor on SOHC
engines and is attached to cylinder head on DOHC engines. If
malfunction occurs, Code 22 will set. For testing procedure, see
appropriate G - TESTS W/CODES article in the ENGINE PERFORMANCE
Section.
EMISSION SYSTEMS & SUB-SYSTEMS
EXHAUST GAS RECIRCULATION (EGR)
System Testing (Federal)
1) Disconnect Green-striped hose from throttle body, and
connect vacuum pump to hose end. Plug nipple where hose was connected
to throttle body. When engine is cold, 122
F (50C) or less, and at
idle, apply vacuum to disconnected hose. If idle does not change and
vacuum bleeds down, system is okay.
2) When engine is hot, 205
F (95C), and at idle, apply 1.8
in. Hg. If idle does not change and vacuum holds, system is okay.
Using a vacuum pump, apply 7.7 in. Hg. If idle becomes unstable or
engine stalls (and vacuum holds), system is okay.
System Testing (California)
1) Connect vacuum "T" fitting into Green-striped hose from
EGR valve, and connect vacuum gauge to vacuum tee. When engine coolant
temperature is 68
F (20C) or less and engine is idling, snap throttle
open to race engine. If no change in vacuum reading is detected on
gauge, system is okay.
2) When engine coolant temperature is 158
F (70C) or more
and engine is idling, snap throttle open to race engine. If vacuum
increases to 3.9 in. Hg or higher, system is okay.
3) Using vacuum pump, apply specified vacuum to open EGR
valve. See EGR VALVE SPECIFICATIONS table. If idle becomes unstable or
engine stalls, system is okay.
EGR Control Solenoid Valve (Pickup & Ram-50, California)
1) EGR control solenoid valve is located near left shock
tower. Label and disconnect vacuum hoses and wiring harness from
solenoid valve.
2) Connect hand vacuum pump to vacuum nipple where Green-
striped vacuum hose was connected. Apply vacuum and ensure vacuum does
not hold. Apply battery voltage to one terminal of solenoid, and
ground other. Ensure vacuum holds.

3) Using an ohmmeter, measure resistance between terminals of
solenoid valve. At room temperature, reading should be 36-44 ohms.
Replace solenoid if not to specification.
NOTE: EGR temperature sensor only determines if EGR is operating.
An inoperative sensor will not affect driveability or
exhaust emissions.
EGR Temperature Sensor (California)
1) Remove EGR temperature sensor from EGR valve. Place EGR
temperature sensor in water. While increasing water temperature,
measure resistance between wire terminals.
2) At a temperature of 122
F (50C), resistance should be 60,
000-80,000 ohms. At 212F (100C), resistance should be 11,000-14,000
ohms. Replace EGR temperature sensor if resistance differs
significantly from specifications.
EGR Valve
1) Remove EGR valve. Check valve for sticking, carbon
deposits and damage. Clean valve with solvent if necessary. Apply 19.8
in. Hg to valve diaphragm. If valve does not hold vacuum, replace
valve.
2) Apply specified vacuum to valve diaphragm. See CLOSED IN.
HG in EGR VALVE SPECIFICATIONS table. If valve begins to open below
specification, replace valve.
3) Apply specified vacuum to valve diaphragm. See OPEN IN. HG
in EGR VALVE SPECIFICATIONS table. If valve is not completely open at
or above specification, replace valve.
EGR VALVE SPECIFICATIONS TABLE









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Application Closed Open
In. Hg In. Hg
Montero ....................... 2.4 ........... 6.7
Pickup & Ram-50 ............... 1.2 ........... 9.4









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FUEL EVAPORATION
System Test
1) Disconnect Red-striped purge hose from throttle body, and
connect to hand vacuum pump. Plug nipple on throttle body where purge
hose was removed.
2) With engine coolant temperature at 140
F (60C) or less
and engine idling, apply 14.8 in. Hg. Vacuum should hold. Raise engine
speed to 3000 RPM and again apply 14.8 in. Hg. Vacuum should hold.
3) With engine coolant temperature at 158
F (70C) or more
and engine idling, apply 14.8 in. Hg. Vacuum should hold. Turn engine
off. Start engine and within 3 minutes of starting engine, apply
vacuum. Vacuum should bleed down.
4) With engine running for more than 3 minutes after
starting, raise engine speed to 3000 RPM and apply 14.8 in. Hg. Vacuum
should hold momentarily and then bleed down.
NOTE: In step 4), vacuum should bleed down continuously if vehicle
is at an altitude of 7200 ft. (2200 m) or higher or if
intake air temperature is 122
F (50C) or higher.
Purge Control Solenoid Valve
1) Purge control solenoid valve is located near left shock
tower. Label and disconnect both vacuum hoses from solenoid valve.
Disconnect electrical connector. Connect hand vacuum pump to solenoid

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G - T E STS W /C O DES
1991 Mitsubishi Montero
1990-91 ENGINE PERFORMANCE
Chrysler Motors/Mitsubishi Self-Diagnostics
Dodge; Colt, Colt Vista, Colt Wagon
Eagle; Summit
Mitsubishi; Eclipse, Galant, Mirage, Montero, Precis (1990)
Plymouth; Colt, Colt Vista, Colt Wagon
INTRODUCTION
If no faults were found while performing F - BASIC TESTING,
proceed with self-diagnostics. If no fault codes or only pass codes
are present after entering self-diagnostics, proceed to H - TESTS W/O
CODES article for diagnosis by symptom (i.e. ROUGH IDLE, NO START,
etc.).
SELF-DIAGNOSTIC SYSTEM
Use Chrysler Motors code charts when using Chrysler's
Diagnostic Readout Box (DRB-II). If DRB-II is not available or if
working on a Mitsubishi Motors vehicle, system diagnosis can only be
accomplished using a voltmeter or appropriate scan tester. To diagnose
Chrysler Motors and Mitsubishi models using a voltmeter, see
ENTERING ON-BOARD DIAGNOSTICS (USING VOLTMETER) in this article.
SYSTEM DIAGNOSIS
SYSTEM DIAGNOSIS DESCRIPTION
NOTE: Chrysler Motors recommends using DRB-II to diagnose system.
Voltmeter usage has limited diagnostic capabilities but can
be used if DRB-II is not available or if working on a
Mitsubishi Motors vehicle.
The Engine Control Unit (ECU) monitors several different
engine control system circuits. If an abnormal input signal occurs, a
fault code is stored in ECU memory and given a fault code number. Each
circuit has its own fault number and message. A specific fault code
indicates a particular system failure, but it DOES NOT indicate that
cause of failure is necessarily within system. A fault code DOES NOT
condemn any specific component; it simply points out a probable
malfunctioning area. If a critical fault code is set, the ECU will
turn on CHECK ENGINE light. All fault codes except speed sensor are
considered critical.
Fault codes can be confirmed by using a voltmeter on Chrysler
Motors and Mitsubishi models or Chrysler's Diagnostic Readout Box
(DRB-II) on Chrysler Motors vehicles. See
ENTERING ON-BOARD DIAGNOSTICS (USING VOLTMETER) or ENTERING ON-BOARD
DIAGNOSTICS (USING DRB-II) in this article. By using the DRB-II, the
self-diagnostic capabilities of this system can simplify testing and
reduce diagnostic time.
System malfunctions encountered are identified as either hard
failures or intermittent failures as determined by the ECU.
HARD FAILURES
Hard failures cause CHECK ENGINE light to illuminate and
remain on until the malfunction is repaired. If light comes on and