1991 MITSUBISHI MONTERO fuel pressure

Air in fuel system Bleed air from system
Incorrect or contaminated Replace fuel
fuel
Injector nozzle malfunction Check nozzles, see
FUEL SYSTEMS









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Engines Starts Injection pump timing Reset pump timing, see
and Idles Rough incorrect FUEL SYSTEMS
W/out Smoke or Engine not fully broken in Put more miles on
Noise, But Clears engine
After Warm-Up Air in system Bleed air from system
Injector nozzle malfunction Check nozzles, see
FUEL SYSTEMS









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Engine Idles Blocked fuel filter Replace fuel filter
Correctly, Injection pump timing Reset pump timing, see
Misfires Above incorrect FUEL SYSTEMS
Idle Incorrect or contaminated Replace fuel
fuel









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Engine Won't Fast idle adjustment Reset fast idle, see
Return To Idle incorrect TUNE-UP
Internal injection pump Replace injection pump,
malfunction see FUEL SYSTEMS
External linkage binding Check linkage and
remove binding









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Fuel Leaks On Loose or broken fuel line Check lines and
Ground connections
Internal injection pump Replace injection pump,
seal leak see FUEL SYSTEMS









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Cylinder Injector nozzles sticking Test injectors, see
Knocking Noise open FUEL SYSTEMS
Very low nozzle opening Test injectors and/or
pressure replace









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Loss of Engine Restricted air intake Remove restriction
Power EGR valve malfunction Replace EGR valve
Blocked or damaged exhaust Remove restriction
system and/or replace
components
Blocked fuel tank filter Replace filter
Restricted fuel filter Remove restriction
and/or replace filter
Block vent in gas cap Remove restriction
and/or replace cap
Tank-to-injection pump fuel Check fuel lines and
supply blocked connections
Blocked fuel return system Remove restriction
Incorrect or contaminated Replace fuel
fuel
Blocked injector nozzles Check nozzle for
blockage, see FUEL
SYSTEMS
Low compression Check valves, rings,
pistons, see ENGINES









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Loud Engine Basic timing incorrect Reset timing, see
Noise With Black FUEL SYSTEMS
Smoke EGR valve malfunction Replace EGR valve
Internal injection pump Replace injection pump,
malfunction see FUEL SYSTEMS

Incorrect injector pump Check pressure, see
housing pressure FUEL SYSTEMS









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Engine Cooling system leaks Check cooling system
Overheating and repair leaks
Belt slipping or damaged Check tension and/or
replace belt
Thermostat stuck closed Remove and replace
thermostat, see
ENGINE COOLING
Head gasket leaking Replace head gasket









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Oil Light on at Low oil pump pressure Check oil pump
Idle operation, see ENGINES
Oil cooler or line Remove restriction
restricted and/or replace cooler









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Engine Won't Injector pump fuel solenoid Remove and check
Shut Off does not return fuel valve solenoid and replace
to OFF position if needed









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VACUUM PUMP DIAGNOSIS
Excessive Noise Loose pump-to-drive Tighten screws
assembly screws
Loose tube on pump assembly Tighten tube
Valves not functioning Replace valves
properly
Oil Leakage Loose end plug Tighten end plug
Bad seal crimp Remove and re-crimp
seal









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FUEL INJECTION 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 FUEL INJECTION TROUBLE SHOOTING CHART









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CONDITION POSSIBLE CAUSE CORRECTION








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Engine Won't Cold start valve inoperative Test valve and
Start (Cranks circuit
Normally)
Poor connection;vacuum or Check vacuum and
wiring electrical
connections
Contaminated fuel Test fuel for water
or alcohol
Defective fuel pump relay Test relay and
or circuit wiring
Battery too low Charge and test
battery

Low fuel pressure Test pressure regul-
ator and fuel pump,
check for restricted
lines and filters
No distributor reference Repair ignition
pulses system as necessary
Open coolant temperature Test sensor and
sensor circuit wiring
Shorted W.O.T. switch in Disconnect W.O.T.
T.P.S. switch, engine
should start
Defective ECM Replace ECM
Fuel tank residual pressure Test for fuel
valve leaks pressure drop after
shut down









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Hard Starting Disconnected hot air tube Reconnect tube and
to air cleaner test control valve
Defective Idle Air Control Test valve operation
(IAC) valve and circuit
Shorted, open or misadjusted Test and adjust or
T.P.S. replace T.P.S.
EGR valve open Test EGR valve and
control circuit
Poor Oxygen sensor signal Test for shorted or
circuit
Incorrect mixture from PCV Test PCV for flow,
system check sealing of oil
filter cap









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Poor High Speed Low fuel pump volume Faulty pump or
Operation restricted fuel
lines or filters
Poor MAP sensor signal Test MAP sensor,
vacuum hose and
wiring
Poor Oxygen sensor signal Test for shorted or
open sensor or
circuit
Open coolant temperature Test sensor and
sensor circuit wiring
Faulty ignition operation Check wires for
cracks or poor con-
nections, test
secondary voltage
with oscilloscope
Contaminated fuel Test fuel for water

or alcohol
Intermittent ECM ground Test ECM ground
connection for
resistance
Restricted air cleaner Replace air cleaner
Restricted exhaust system Test for exhaust
manifold back
pressure
Poor MAF sensor signal Check leakage
between sensor and
manifold
Poor VSS signal If tester for ALCL
hook-up is available
check that VSS
reading matches
speedometer









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Ping or Knock on Poor Knock sensor signal Test for shorted or
Acceleration open sensor or
circuit
Poor Baro sensor signal Test for shorted or
open sensor or
circuit
Improper ignition timing See VEHICLE EMISSION
CONTROL LABEL (where
applicable)
Check for engine Low coolant, loose
overheating problems belts or electric
cooling fan
inoperative









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NOTE: For additional electronic fuel injection trouble shooting
information, see the appropriate article in the ENGINE
PERFORMANCE section (not all vehicles have Computer Engine
Control articles). Information is provided there for
diagnosing fuel system problems on vehicles with electronic
fuel injection.
IGNITION 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.
Ignition Secondary Trouble Shooting Chart








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START: Visually inspect Spark Plug Wires, Coil Wires, 

Plug Wire Boots, Rotor, and Distributor Cap for 

signs of damage.