check engine MITSUBISHI MONTERO 1991 Service Manual

* Check motor position sensor (if applicable).
* Check fuel pressure.
* Check for disconnected or damaged vacuum hoses.
* Check for PFI system malfunction.
* Check for stepper motor malfunction (if applicable).
* Check for fuel injector malfunction.
* Check for power transistor malfunction.
* Check for A/C power relay control system malfunction (if
applicable).
* Check for ECU malfunction.
* Ensure electrical harness, connectors and wires are not
broken or loose.
ENGINE SURGES
* Check coolant temperature sensor.
* Check idle position switch.
* Check EGR control solenoid valve (if applicable).
* Check fuel pressure.
* Check for fuel injector malfunction.
DETONATION OR KNOCKING
* Check airflow sensor.
* Check for cooling system problems.
* Check fuel quality.
* Check intake air temperature sensor.
* Check barometric pressure sensor.
* Check ignition coil.
* Check power transistor.
* Check for EGR system malfunction.
POOR FUEL MILEAGE
* Check intake air temperature sensor.
* Check engine coolant temperature sensor.
* Check barometric pressure sensor.
* Check ignition switch.
* Check idle position switch.
* Check throttle position sensor.
* Check TDC sensor.
* Check crank angle sensor.
* Check power steering oil pressure switch.
* Check A/C switch (if applicable).
* Check inhibitor switch (A/T).
* Check oxygen sensor.
* Check airflow sensor.
* Check motor position sensor (if applicable).
* Check fuel pressure.
* Check for PFI system malfunction.
* Check for stepper motor malfunction.
* Check for fuel injector malfunction.
* Check for power transistor malfunction.
INTERMITTENTS
INTERMITTENT PROBLEM DIAGNOSIS
Intermittent fault testing requires duplicating circuit or
component failure to identify problem. These procedures may lead to
computer setting a fault code which may help in diagnosis.
If problem vehicle does not produce fault codes, monitor

Inhibitor Switch (Automatic Transmission Only)
Inhibitor switch senses position of transmission select
lever, indicating engine load due to automatic transmission
engagement. Based on this signal, ECU commands ISC motor to increase
throttle angle, maintaining optimum idle speed.
Intake Air Temperature Sensor
Incorporated in airflow sensor assembly, this resistor-based
sensor measures temperature of incoming air and supplies air density
information to ECU.
Motor Position Sensor (MPS)
Incorporated in ISC motor (or separate unit on some models),
senses ISC motor plunger position and sends electrical signal to ECU.
Oxygen (O2) Sensor
Located in exhaust system, generates an output voltage.
Output voltage varies with oxygen content of exhaust gas stream. ECU
adjusts air/fuel mixture based on signals from oxygen sensor.
Power Steering Oil Pressure Switch
Detects increase in power steering oil pressure. When power
steering oil pressure increases, switch contacts close, signalling
ECU. ECU commands ISC motor, raising idle speed to compensate for drop
in engine RPM due to power steering load.
TDC Sensor
See CRANKSHAFT ANGLE & TDC SENSOR ASSEMBLY.
Throttle Position Sensor (TPS)
A variable resistor mounted on throttle body. ECU uses
voltage signal received from TPS to determine throttle plate angle.
Vehicle Speed Sensor
Located in speedometer in instrument cluster, uses a reed
switch to sense speedometer gear revolutions. ECU uses gear
revolutions to determine vehicle speed.
OUTPUT SIGNALS
NOTE: Vehicles are equipped with different combinations of
computer-controlled components. Not all components listed
below are used on every vehicle. For theory and operation on
each output component, refer to the system indicated in
brackets after component.
CHECK ENGINE Light
See SELF DIAGNOSTIC SYSTEM.
EGR Control Solenoid Valve
See EXHAUST GAS RECIRCULATION (EGR) CONTROL under EMISSION
SYSTEMS.
Fuel Injectors
See FUEL CONTROL under FUEL SYSTEM.
Fuel Pressure Control Solenoid Valve (Turbo Only)
See FUEL DELIVERY under FUEL SYSTEM.
Fuel Pressure Regulator
See FUEL DELIVERY under FUEL SYSTEM.
Fuel Pump Relay (MPI Control Relay)

See FUEL DELIVERY under FUEL SYSTEM.
Idle Speed Control Servo
See IDLE SPEED under FUEL SYSTEM.
Power Transistor(s) & Ignition Coils
See IGNITION SYSTEMS.
Purge Control Solenoid Valve
See EVAPORATIVE CONTROL under EMISSION SYSTEMS.
Self-Diagnostic Connector
See SELF-DIAGNOSTIC SYSTEM.
Wastegate Control Solenoid Valve
See TURBOCHARGED ENGINES under AIR INDUCTION SYSTEM.
FUEL SYSTEM
FUEL DELIVERY
Electric fuel pump (located in gas tank) feeds fuel through
in-tank fuel filter, external fuel filter (located in engine
compartment) and fuel injector rail.
Fuel Pump
Consists of an impeller driven by a motor. Pump has an
internal check valve to maintain system pressure and a relief valve to
protect the fuel pressure circuit. Pump receives voltage supply from
Multi-Point Injection (MPI) control relay.
Fuel Pressure Control Solenoid Valve (Turbo Only)
Prevents rough idle due to fuel percolation. On engine
restart, if engine coolant or intake air temperatures reach a preset
value, ECU applies voltage to fuel pressure control solenoid valve for
2 minutes after engine re-start. Valve opens, allowing atmospheric
pressure to be applied to fuel pressure regulator diaphragm. This
allows maximum available fuel pressure at injectors, enriching fuel
mixture and maintaining stable idle at high engine temperatures.
Fuel Pressure Regulator
Located on fuel injector rail, this diaphragm-operated relief
valve adjusts fuel pressure according to engine manifold vacuum.
As engine manifold vacuum increases (closed throttle), fuel
pressure regulator diaphragm opens relief valve, allowing pressure to
bleed off through fuel return line, reducing fuel pressure.
As engine manifold vacuum decreases (open throttle), fuel
pressure regulator diaphragm closes valve, preventing pressure from
bleeding off through fuel return line, increasing fuel pressure.
FUEL CONTROL
Fuel Injectors
Fuel is supplied to engine through electronically pulsed
(timed) injector valves located on fuel rail(s). ECU controls amount\
of fuel metered through injectors based upon information received from
sensors.
IDLE SPEED
Air Conditioner Relay
When A/C is turned on with engine at idle, ECU signals ISC

EMISSION SYSTEMS
EXHAUST GAS RECIRCULATION (EGR) CONTROL
Federal (Non-Turbocharged)
To lower oxides of nitrogen (NOx) exhaust emissions, a non-
computer controlled exhaust gas recirculation system is used. EGR
operation is controlled by throttle body ported vacuum. Vacuum is
routed through thermovalve to prevent EGR operation at low engine
temperatures.
Spring pressure holds EGR valve closed during low vacuum
conditions (engine idling or wide open throttle). When vacuum pressure\
increases and overcomes EGR spring pressure, EGR valve is lifted and
allows exhaust gases to flow into intake manifold for combustion.
California & Turbocharged
ECU controls EGR operation by activating EGR control solenoid
valve according to engine load. When engine is cold, ECU signals EGR
control solenoid valve to deactivate EGR.
California models are equipped with an EGR temperature
sensor. When EGR malfunction occurs, EGR temperature decreases and ECU
illuminates CHECK ENGINE (malfunction indicator) light.
EGR Control Solenoid Valve
Denies or allows vacuum supply to EGR valve, based upon ECU
commands.
Thermovalve
Denies or allows vacuum supply to EGR valve based on coolant
temperature.
EVAPORATIVE CONTROL
Fuel evaporation system prevents fuel vapor from entering
atmosphere. System consists of a special fuel tank with vapor
separator tanks (if equipped), vacuum relief filler cap, overfill
limiter (2-way valve), fuel check valve, thermovalve (if equipped),
charcoal canister, purge control valve, purge control solenoid valve
and connecting lines and hoses.
Purge Control Solenoid Valve
When engine is off, fuel vapors are vented into charcoal
canister. When engine is warmed to normal operating temperature and
running above idle, ECU energizes purge control solenoid valve,
allowing vacuum to purge valve.
Canister vapors are then drawn through purge valve into
intake manifold for burning. Purge control solenoid valve remains
closed during idle and engine warm-up to reduce HC and CO emissions.
HIGH ALTITUDE CONTROL (HAC)
This system compensates for variations in altitude. When
atmospheric (barometric) pressure sensor determines vehicle is above
preset altitude, ECU compensates by adjusting air/fuel mixture and
ignition timing. If HAC system is inoperative, there will be an
increase in emissions.
PCV VALVE
Positive Crankcase Ventilation (PCV) valve operates in the
closed crankcase ventilation system. Closed crankcase ventilation

system consists of PCV valve, oil separator, breather and ventilation
hoses.
PCV valve is a one-way check valve, located in valve cover.
When engine is running, manifold vacuum pulls PCV valve open, allowing
crankcase fumes to enter intake manifold. If engine backfires through
intake manifold, PCV valve closes to prevent crankcase combustion.
SELF-DIAGNOSTIC SYSTEM
Self-diagnostic system monitors input and output signals. On
all models, codes can be read using analog voltmeter. On some models,
scan tool can be used to read codes. For additional information, see G
- TESTS W/ CODES article.
CHECK ENGINE Light
Also called Malfunction Indicator Light by manufacturer,
comes on when ignition is turned on. Light remains on for several
seconds after engine has started. If an abnormal input signal occurs,
light comes on and code is stored in memory. If an abnormal input
signal returns to normal, ECU turns light off but code remains stored
in memory until cleared. If ignition is turned on again, light will
not come on until ECU detects malfunction during system operation.
NOTE: ECU diagnostic memory is retained by direct power supply
from the battery. Memory is not erased by turning off
ignition but is erased if battery or ECU is disconnected.

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TR AN SM IS SIO N S ER VIC IN G - A /T

1991 M it s u bis h i M onte ro
1991 TRANSMISSION SERVICING
Automatic Transmission
Mitsubishi: Eclipse, Galant, Mirage,
Montero, Pickup, Precis, 3000GT
IDENTIFICATION
MITSUBISHI AUTOMATIC TRANSMISSION APPLICATIONS








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Model Transmission/Transaxle
Eclipse
1.8 & 2.0L ........................... Model F4A22 Transaxle
2.0L Turbo ........................... Model F4A33 Transaxle
All-Wheel Drive (AWD) ................ Model W4A33 Transaxle
Galant
AWD .................................. Model W4A32 Transaxle
DOHC ................................. Model F4A22 Transaxle
SOHC ........................ Model KM175 or F4A22 Transaxle
Mirage
1.5L ................................. Model F3A21 Transaxle
1.6L ................................. Model F4A21 Transaxle
Montero ............................ Model V4AW2 Transmission
Pickup ............................. Model R4AC1 Transmission
Precis ................................ Model KM176 Transaxle
3000GT ................................ Model F4A33 Transaxle









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LUBRICATION
TRANSAXLE/TRANSMISSION SERVICE INTERVALS
Check fluid level every 12 months or 15,000 miles. Change
fluid and filter every 30,000 miles. If vehicle is operated under
severe condition, change fluid more often. If severe darkening of
fluid and strong odor are noted, bands should also be adjusted (if
equipped).
TRANSFER CASE SERVICE INTERVALS
On 4WD and AWD models, change transfer case fluid every 30,
000 miles.
CHECKING FLUID LEVEL
TRANSAXLE/TRANSMISSION
1) Park vehicle on level area. Ensure oil is at normal
operating temperature, parking brake is engaged, and engine is at
idle. Move gear selector through each position, stopping briefly in
each position.
2) Place gear selector in Neutral, and clean area around
dipstick tube. Ensure fluid level is between lower and upper marks,
but never over upper mark, in HOT range. Add or drain fluid if
necessary.

oil filter/screen, note length and location of all bolts.
TRANSAXLE (EXCEPT MONTERO, PICKUP & RAM-50)
1) Remove drain plug(s), and drain fluid. See Fig. 1. Some
applications may contain a drain plug located in housing below drive
axle shaft, in oil pan. Remove oil pan. Remove oil filter/screen if
necessary.
2) If oil filter/screen is replaced, tighten bolts to
specification. See TORQUE SPECIFICATIONS table at end of article.
Clean oil pan, replace gasket, and install oil pan. Tighten oil pan
bolts and drain plug to specification. See TORQUE SPECIFICATIONS
table. Ensure dipstick hole area is clean, and pour approximately 4.2
qts. (4.0L) of Dexron-II fluid into dipstick hole.
3) Operate engine at idle for 2 minutes. Shift transaxle to
each position, ending in Neutral. Add sufficient fluid to reach lower
mark. After reaching normal operating temperature, fluid should be
between upper and lower marks of HOT range on dipstick.
Fig. 1: Locating Drain Plugs
Courtesy of Mitsubishi Motor Sales of America.
TRANSMISSION (MONTERO & PICKUP)
1) Remove drain plug (if equipped) from transmission pan, an\
d
allow fluid to drain. On models without drain plug, remove oil pan
must to drain fluid. Remove oil filter/screen if necessary.
2) If oil filter/screen is replaced, tighten bolts to
specification. See TORQUE SPECIFICATIONS table at end of article.
Clean oil pan, replace gasket, and install oil pan. Tighten oil pan
bolts and drain plug to specification. See TORQUE SPECIFICATIONS
table. Fill transmission, through filler tube, with 5.3 qts. (5.0L) of\
Dexron-II ATF on Montero, or 2.0 qts. (1.9L) on all others. Start
engine, and allow to idle for 2 minutes.
3) Shift transmission into each position, ending in Neutral.
Check fluid level with engine running at idle, and add sufficient

fluid to bring level to lower mark of dipstick if necessary. Recheck
fluid level after transmission is at normal operating temperature.
TRANSFER CASE
Drain plug is located on bottom of transfer case. Change
drain plug gasket whenever fluid is changed. On 3000GT, lubricant
level should be approximately .5" (13 mm) below fill hole on side of
transfer case. On all others models, lubricant level should be to
bottom of fill hole on side of transfer case.
HYDRAULIC CONTROL PRESSURE ADJUSTMENTS
LINE PRESSURE CHECK (EXCEPT MONTERO & PICKUP)
1) Set parking brake. Place shift lever in Neutral position.
Attach engine tachometer. Remove line pressure port plug located above
front transaxle shaft, forward of governor pressure port plug. On
Precis, line pressure port is located below bell housing, at front of
transaxle oil pan. Using appropriate adapter, attach pressure gauge.
2) Start engine, and bring to operating temperature. With
gear selector in Drive position, bring engine speed to 2500 RPM. Pull
throttle control cable (if equipped) wide open at transaxle side.
3) Line pressure should be 98-100 psi (6.9-7.0 kg/cm
) on
Mirage, or 124-127 psi (8.7-8.9 kg/cm) on all others. If line
pressure is not to specification, proceed to LINE PRESSURE ADJUSTMENT.
LINE PRESSURE ADJUSTMENT (EXCEPT MONTERO & PICKUP)
1) Drain transaxle fluid. Remove oil pan. Disconnect throttle
control cable from throttle cam. Remove oil temperature sensor (if
equipped). Disconnect solenoid connector. On some models, it may be
necessary to push solenoid wire harness connector and grommet into
transaxle case.
2) Remove oil filter screen and plate. Noting location and
length of bolts, remove valve body. DO NOT drop internal parts. Adjust
line pressure by turning regulator valve adjusting screw.
3) Turn adjusting screw counterclockwise to increase pressure
or clockwise to decrease pressure. One complete turn of adjusting
screw changes line pressure as follows.
* 3.7 psi (.26 kg/cm
) on Mirage with F3A21 Transaxle
* 5.4 psi (.39 kg/cm) on Precis
* 54 psi (3.8 kg/cm) on all others
4) After adjustment, reverse removal procedure to install.
Refill transaxle.
LINE PRESSURE (MONTERO)
1) Remove plug from line pressure take-off port located
behind transmission shift control lever. Install Hydraulic Pressure
Meter (MD998330) with Adapter (MD998206).
2) Place vehicle on dynamometer. Apply parking brake and
start engine. With brake applied, place transmission in Drive. Note
pressure at idle. Pressure should be 74-85 psi (5.2-6.0 kg/cm
).
3) Raise engine RPM to stall speed (2100-2400 RPM). Note lin\
e
pressure. Pressure should be 156-185 psi (11.0-13.0 kg/cm
).
4) Shift transmission into Reverse with brake applied. At
idle, pressure should be 112-130 psi (7.9-9.1 kg/cm
). Raise engine
RPM to stall speed (2100-2400 RPM). Note line pressure. Pressure
should be 227-285 psi (16.0-20.0 kg/cm
). If readings are not to

PICKUP
1) Ensure engine idle is adjusted correctly. Ensure throttle
lever and throttle cable bracket are not bent. Pull lightly on inner
throttle cable.
2) While in closed throttle position, measure gap between
inner cable stopper and outer cable housing. Adjust cable as necessary
to obtain a gap of .031-.059" (.79-1.50 mm). See Fig. 4 (STEP 1).
Fig. 4: Adjusting Throttle Cable (Pickup)
Courtesy of Mitsubishi Motor Sales of America.
3) While holding throttle in wide open position, pull on
inner throttle cable. Adjust bell crank as necessary to obtain a gap
of 1.46-1.50" (37.08-38.10 mm) between inner cable stopper and outer
cable. See Fig. 4 (STEP 2).
4) With throttle fully closed, recheck gap between inner
cable stopper and outer cable housing. Gap should be .031-.059" (.79-
1.50 mm). See Fig. 4 (STEP 3). While holding throttle in wide open
position, pull on inner throttle cable. Check for a gap of 1.30-1.38"
(33.02-35.05 mm).
Montero Ensure throttle lever and throttle cable bracket
are not bent. Ensure distance between inner cable stopper end and dust
cover is 0-.04" (0-1.0 mm). See Fig. 5.
Fig. 5: Adjusting Throttle Cable (Montero)
Courtesy of Mitsubishi Motor Sales of America.
SHIFT LINKAGE

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TR O UBLE S H O OTIN G - B ASIC P R O CED URES

1991 M it s u bis h i M onte ro
GENERAL TROUBLE SHOOTING
* PLEASE READ THIS FIRST *
NOTE: This is GENERAL information. This article is not intended
to be specific to any unique situation or individual vehicle
configuration. The purpose of this Trouble Shooting
information is to provide a list of common causes to
problem symptoms. For model-specific Trouble Shooting,
refer to SUBJECT, DIAGNOSTIC, or TESTING articles available
in the section(s) you are accessing.
ACCESSORIES & ELECTRICAL
CHARGING SYSTEM TROUBLE SHOOTING
NOTE: This is GENERAL information. This article is not intended
to be specific to any unique situation or individual vehicle
configuration. The purpose of this Trouble Shooting
information is to provide a list of common causes to
problem symptoms. For model-specific Trouble Shooting,
refer to SUBJECT, DIAGNOSTIC, or TESTING articles available
in the section(s) you are accessing.
BASIC CHARGING SYSTEM TROUBLE SHOOTING CHART









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CONDITION POSSIBLE CAUSE CORRECTION








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Vehicle Will Not Dead battery Check battery cells,
Start alternator belt
tension and alternator
output
Loose or corroded battery Check all charging
connections system connections
Ignition circuit or switch Check and replace as
malfunction necessary









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Alternator Light Loose or worn alternator Check alternator drive
Stays On With drive belt tension and
Engine Running condition, See Belt
Adjustment in TUNE-UP
article in the
TUNE-UP section
Loose alternator wiring Check all charging
connections system connections
Short in alternator light See Indicator Warning
wiring Lights in STANDARD
INSTRUMENTS in the
ACCESSORIES &
EQUIPMENT section
Defective alternator stator See Bench Tests in
or diodes ALTERNATOR article
Defective regulator See Regulator Check in