1991 MITSUBISHI MONTERO power steering

* Check airflow sensor.
* Check coolant temperature sensor.
* Check idle position switch.
* Check power supply to ECU ground.
* Check fuel pressure.
* Check for disconnected or damaged vacuum hoses.
* Check for control relay malfunction.
* Check for PFI system malfunction.
* Check for fuel pump drive control system malfunction.
* Check for ignition coil malfunction.
* Check for ignition timing malfunction.
* Check for power transistor malfunction.
* Check for fuel injector malfunction.
* Check for ECU malfunction.
* Ensure electrical harness, connectors and wires are not
broken or loose.
ROUGH OR UNSTABLE IDLE
* Check intake air temperature sensor.
* Check purge control solenoid valve (if applicable).
* Check vehicle speed 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 and power relay (if applicable).
* Check inhibitor switch.
* Check oxygen sensor.
* Check airflow sensor.
* Check motor position sensor (if equipped).
* Check fuel pressure.
* Check for disconnected or damaged vacuum hoses.
* Check PFI system malfunction.
* Check for stepper motor malfunction (if applicable).
* Check for fuel injector malfunction.
* Check for power transistor malfunction.
* Check for vehicle speed switch malfunction.
* Check for ECU malfunction.
* Ensure electrical harness, connectors and wires are not
broken or loose.
ENGINE HESITATES OR POOR ACCELERATION
* Check intake air temperature sensor.
* Check engine coolant temperature sensor.
* Check barometric pressure sensor.
* Check ignition switch.
* Check ignition coil.
* Check EGR control solenoid valve (if applicable).
* 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 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)

motor to increase idle speed. To prevent A/C compressor from switching
on before idle speed has increased, ECU momentarily opens A/C relay
circuit.
Idle Speed Control (ISC) Motor
Controls pintle-type air valve (DOHC engines) or throttle
plate angle (SOHC engines) to regulate volume of intake air at idle.
During start mode, ECU controls idle intake air volume
according to coolant temperature input. After starting, with idle
position switch activated (throttle closed), fast idle speed is
controlled by ISC motor and fast idle air control valve (if equipped).\
When idle switch is deactivated (throttle open), ISC motor
moves to a preset position in accordance with coolant temperature
input.
When automatic transmission (if equipped) is shifted from
Neutral to Drive, A/C is turned on or power steering pressure reaches
a preset value, ECU signals ISC motor to increase engine RPM.
Fast Idle Air Control Valve
Some models use a coolant temperature-sensitive fast idle air
control valve, located on throttle body, to admit additional intake
air volume during engine warm-up. Control valve closes as temperature
increases, restricting by-pass airflow rate. At engine warm-up, valve
closes completely.
IGNITION SYSTEMS
DIRECT IGNITION SYSTEM (DIS) - DOHC ENGINES
Ignition system is a 2-coil, distributorless ignition system.
Crankshaft angle and TDC sensor assembly, mounted in place of
distributor, are optically controlled.
Power Transistors & Ignition Coils
Based on crankshaft angle and TDC sensor inputs, ECU controls
timing and directly activates each power transistor to fire coils.
Power transistor "A" controls primary current of ignition coil "A" to
fire spark plugs on cylinders No. 1 and 4 at the same time. Power
transistor "B" controls primary current of ignition coil "B" to fire
spark plugs on cylinders No. 2 and 3 at the same time.
Although each coil fires 2 plugs at the same time, ignition
takes place in only one cylinder since the other cylinder is on its
exhaust stroke when plug fires.
ELECTRONIC IGNITION SYSTEM - SOHC ENGINES
Mitsubishi breakerless electronic ignition system uses a disc
and optical sensing unit to trigger power transistor.
Power Transistor & Ignition Coil
Power transistor is mounted inside distributor with disc and
optical sensing unit. When ignition is on, ignition coil primary
circuit is energized. As distributor shaft rotates, disc rotates,
triggering optical sensing unit. ECU receives signals from optical
sensing unit. Signals are converted and sent to power transistor,
interrupting primary current flow and inducing secondary voltage.
IGNITION TIMING CONTROL SYSTEM
Ignition timing is controlled by ECU. ECU adjusts timing
based upon various conditions, such as engine temperature, altitude
and detonation (turbo vehicles only).

Brakes dragging See BRAKES article








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Instability Low or uneven tire Inflate to proper
pressure pressure
Loose or worn wheel See FRONT SUSPENSION
bearings article
Loose or worn idler arm See FRONT SUSPENSION
bushing article
Loose or worn strut See FRONT SUSPENSION
bushings article
Incorrect front wheel See WHEEL ALIGNMENT
alignment article
Steering gear not See MANUAL STEERING
centered GEARS article
Springs or shock Check and replace if
necessary
Improper cross shaft See MANUAL STEERING
GEARS article









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POWER STEERING 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 POWER STEERING TROUBLE SHOOTING CHART









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CONDITION POSSIBLE CAUSE CORRECTION








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Rattle or Pressure hoses touching Adjust to proper
Chucking Noise engine parts clearance
Loose Pitman shaft Adjust or replace if
necessary
Tie rods ends or Pitman Tighten and check system
arm loose
Rack and pinion mounts Tighten all mounting
loose bolts
Free play in worm and See POWER STEERING GEAR
article
Loose sector shaft or See POWER STEERING GEAR
thrust bearing adjustment
Free play in pot coupling See STEERING COLUMN
article

Worn shaft serrations See STEERING COLUMN
article









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Growl in Excessive pressure in Restricted hoses, see
Steering Pump hoses POWER STEERING GEAR
article
Scored pressure plates See POWER STEERING GEAR
article
Scored thrust plates or See POWER STEERING GEAR
rotor article
Extreme wear of cam ring See POWER STEERING GEAR
article









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Rattle in Vanes not installed See POWER STEERING PUMP
Steering Pump article
Vanes sticking in rotor See POWER STEERING PUMP
article









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Swish noise in Defective flow control See POWER STEERING PUMP
Pump valve article









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Groan in Air in fluid See POWER STEERING PUMP
Steering Pump article
Poor pressure hose Tighten and check,
connection replace if necessary









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Squawk When Damper "O" ring on valve See POWER STEERING PUMP
Turning spool cut article









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Moan or Whine Pump shaft bearing scored Replace bearing and
in Pump fluid
Air in fluid or fluid See POWER STEERING PUMP
level low article
Hose or column grounded Check and replace if
necessary
Cover "O" ring missing See POWER STEERING PUMP
or damaged article
Valve cover baffle See POWER STEERING PUMP
missing or damaged article
Interference of See POWER STEERING PUMP
components in pump article
Loose or poor bracket Correct or replace if
alignment necessary









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Hissing When Internal leakage in Check valved assembly
Parking steering gear first









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Chirp in Loose or worn power Adjust or replace if
Steering Pump steering belt necessary









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Buzzing When Noisy pump See POWER STEERING PUMP
Not Steering article

Free play in steering See STEERING COLUMN
shaft bearing article
Bearing loose on shaft See STEERING COLUMN
serrations article









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Clicking Noise Pump slippers too long See POWER STEERING PUMP
in Pump article
Broken slipper springs See POWER STEERING PUMP
article
Excessive wear or nicked See POWER STEERING PUMP
rotors article
Damaged cam contour See POWER STEERING PUMP
article









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Poor Return of Wheel rubbing against See STEERING COLUMN
Wheel turn signal SWITCHES article
Flange rubbing steering See STEERING COLUMN
gear adjuster article
Tight or frozen steering See STEERING COLUMN
shaft bearing article
Steering gear out of See POWER STEERING GEAR
adjustment article
Sticking or plugged See POWER STEERING PUMP
spool valve article
Improper front end See WHEEL ALIGNMENT
alignment article
Wheel bearings worn or See FRONT SUSPENSION
loose article
Ties rods or ball joints Check and replace if
binding necessary
Intermediate shaft joints See STEERING COLUMN
binding article
Kinked pressure hoses Correct or replace if
necessary
Loose housing head See POWER STEERING GEAR
spanner nut article
Damaged valve lever See POWER STEERING GEAR
article
Sector shaft adjusted See ADJUSTMENTS in POWER
too tight STEERING GEAR article
Worm thrust bearing See ADJUSTMENTS in POWER
adjusted too tight STEERING GEAR article
Reaction ring sticking See POWER STEERING GEAR
in cylinder article

Reaction ring sticking See POWER STEERING GEAR
in housing head article
Steering pump internal See POWER STEERING PUMP
leakage article
Steering gear-to-column See STEERING COLUMN
misalignment article
Lack of lubrication in Service front suspension
linkage
Lack of lubrication in Service front suspension
ball joints









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Increased Effort High internal pump leakage See POWER STEERING PUMP
When Turning article
Wheel Fast Power steering pump belt Adjust or replace if
Foaming, Milky slipping necessary
Power Steering
Fluid, Low Fluid Low fluid level Check and fill to
Level or Low proper level
Pressure
Engine idle speed to low Adjust to correct
setting
Air in pump fluid system See POWER STEERING PUMP
article
Pump output low See POWER STEERING PUMP
article
Steering gear See POWER STEERING GEAR
malfunctioning article









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Wheel Surges Low fluid level Check and fill to proper
or Jerks level
Loose fan belt Adjust or replace if
necessary
Insufficient pump See POWER STEERING PUMP
pressure article
Sticky flow control valve See POWER STEERING PUMP
article
Linkage hitting oil pan Replace bent components
at full turn









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Kick Back or Air in pump fluid system See POWER STEERING PUMP
Free Play article
Worn poppet valve in See POWER STEERING PUMP
steering gear article
Excessive over center See POWER STEERING GEAR
lash article
Thrust bearing out of See POWER STEERING GEAR
adjustment article