1991 MITSUBISHI MONTERO check engine

Spark control systems are designed to ensure the air/fuel
mixture is ignited at the best possible moment to provide optimum
efficiency and power and cleaner emissions.
Ensure vacuum hoses to the distributor, carburetor, spark
delay valves, thermal vacuum switches, etc., are in place and routed
properly. On Computerized Engine Controls (CEC), check for presence of\
required sensors (O2, MAP, CTS, TPS, etc.). Ensure they have not been
tampered with or modified.
Check for visible modification or replacement of the feedback
carburetor, fuel injection unit or injector(s) with a non-feedback
carburetor or fuel injection system. Check for modified emission-
related components unacceptable for use on pollution-controlled
vehicles.
AIR INJECTION SYSTEM (AIS)
Air Pump Injection System (AP)
The air pump is a belt-driven vane type pump, mounted to
engine in combination with other accessories. The air pump itself
consists of the pump housing, an inner air cavity, a rotor and a vane
assembly. As the vanes turn in the housing, filtered air is drawn in
through the intake port and pushed out through the exhaust port. See
Fig. 13 .
Check for missing or disconnected belt, check valve(s),
diverter valve(s), air distribution manifolds, etc. Check air
injection system for proper hose routing.
Fig. 13: Typical Air Pump Injection System
Courtesy of General Motors Corp.
Pulsed Secondary Air Injection (PAIR) System
PAIR eliminates the need for an air pump and most of the
associated hardware. Most systems consists of air delivery pipe(s),
pulse valve(s) and check valve(s). The check valve prevents exhaust
gases from entering the air injection system. See Fig. 14.
Ensure required check valve(s), diverter valve(s), air
distribution manifolds, etc., are present. Check air injection system
for proper hose routing.

EARLY FUEL EVAPORATION (EFE)
The EFE valve is actuated by either a vacuum actuator or a
bimetal spring (heat-riser type). The EFE valve is closed when engine
is cold. The closed valve restricts exhaust gas flow from the exhaust
manifold. This forces part of the exhaust gas to flow up through a
passage below the carburetor. As the exhaust gas quickly warms the
intake mixture, distribution is improved. This results in better cold
engine driveability, shorter choke periods and lower emissions.
Ensure EFE valve in exhaust manifold is not frozen or rusted
in a fixed position. On vacuum-actuated EFE system, check EFE thermal
vacuum valve and check valve(s). Also check for proper vacuum hose
routing. See Fig. 15.
Fig. 15: Typical Vacuum-Actuated EFE System
Courtesy of General Motors Corp.
EMISSION MAINTENANCE REMINDER LIGHT (EMR) (IF EQUIPPED)

If equipped, the EMR light (some models may use a reminder
flag) reminds vehicle operator that an emission system maintenance is
required. This indicator is activated after a predetermined
time/mileage.
When performing a smog check inspection, ensure EMR indicator
is not activated. On models using an EMR light, light should glow when
ignition switch is turned to ON position and should turn off when
engine is running.
If an EMR flag is present or an EMR light stays on with
engine running, fail vehicle and service or replace applicable
emission-related components. To reset an EMR indicator, refer to
appropriate MAINTENANCE REMINDER LIGHTS in the MAINTENANCE section.
MALFUNCTION INDICATOR LIGHT (MIL)
The Malfunction Indicator Light (MIL) is used to alert
vehicle operator that the computerized engine control system has
detected a malfunction (when it stays on all the time with engine
running). On some models, the MIL may also be used to display trouble
codes.
As a bulb and system check, malfunction indicator light will
glow when ignition switch is turned to ON position and engine is not
running. When engine is started, light should go out.

EN G IN E C O OLIN G F A N
1991 M it s u bis h i M onte ro
1991 ENGINE COOLING
Mitsubishi Engine Cooling Fans
Mitsubishi: Eclipse, Galant, Mirage,
Montero, Pickup, Precis, 3000GT
ELECTRIC COOLING FAN - COMPONENT TESTING
MOTOR
Disconnect electric cooling fan motor at junction. Using 2
jumper wires, ground one lead and apply battery voltage to other. Fan
should rotate. If fan does not rotate, replace motor.
RADIATOR FAN SWITCH
Using an ohmmeter, check switch continuity in hot water.
Switch should be open at less than 180F (82C) and continuity should
exist at more than 185F (85C). Replace radiator fan switch if it
does not test as specified.
ELECTRIC COOLING FAN RELAY
1) Remove relay from relay box in front of right suspension
tower. Using jumper wires, connect battery to indicated terminals.
2) On 3000GT, continuity should exist between terminals No. 1
and 3. With battery disconnected, continuity should exist between
terminals No. 2 and 4 and should not exist between terminals No. 1 and
3.
3) On all other models, continuity should exist between
terminals No. 3 and 4. With battery disconnected, continuity should
exist between terminals No. 1 and 2 and should not exist between
terminals No. 3 and 4. Replace relay if it does not test as specified.
Fig. 1: Testing Electric Cooling Fan Relay (except 3000GT)
Courtesy of Mitsubishi Motor Sales of America.

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EN G IN E O VER HAU L P R O CED URES - G EN ER AL IN FO RM ATIO N

1991 M it s u bis h i M onte ro
Engine Overhaul Procedures - General Information
ALL PISTON ENGINES
* PLEASE READ THIS FIRST *
Examples used in this article are general in nature and do
not necessarily relate to a specific engine or system. Illustrations
and procedures have been chosen to guide mechanic through engine
overhaul process. Descriptions of processes of cleaning, inspection,
assembly and machine shop practice are included.
Always refer to appropriate engine overhaul article in the
ENGINES section for complete overhaul procedures and specifications
for the vehicle being repaired.
ENGINE IDENTIFICATION
The engine may be identified from its Vehicle Identification
Number (VIN) stamped on a metal tab. Metal tab may be located in
different locations depending on manufacturer. Engine identification
number or serial number is located on cylinder block. Location varies
with manufacturer.
INSPECTION PROCEDURES
* PLEASE READ THIS FIRST *
NOTE: Always refer to appropriate engine overhaul article in the
ENGINES section for complete overhaul procedures and
specifications for the vehicle being repaired.
GENERAL
Engine components must be inspected to meet manufacturer's
specifications and tolerances during overhaul. Proper dimensions and
tolerances must be met to obtain proper performance and maximum engine
life.
Micrometers, depth gauges and dial indicator are used for
checking tolerances during engine overhaul. Magnaflux, Magnaglo, dye-
check, ultrasonic and x-ray inspection procedures are used for parts
inspection.
MAGNETIC PARTICLE INSPECTION
Magnaflux & Magnaglo
Magnaflux is an inspection technique used to locate material
flaws and stress cracks. The part in question is subjected to a strong
magnetic field. The entire part, or a localized area, can be
magnetized. The part is coated with either a wet or dry material that
contains fine magnetic particles.
Cracks which are outlined by the particles cause an
interruption in the magnetic field. The dry powder method of Magnaflux
can be used in normal light. A crack will appear as an obvious bright
line.
Fluorescent liquid is used in conjunction with a blacklight
in a second Magnaflux system called Magnaglo. This type of inspection
demands a darkened room. The crack will appear as a glowing line in
this process. Both systems require complete demagnetizing upon

completion of the inspection. Magnetic particle inspection applies to
ferrous materials only.
PENETRANT INSPECTION
Zyglo
The Zyglo process coats the material with a fluorescent dye
penetrant. The part is often warmed to expand cracks that will be
penetrated by the dye. When the coated part is subjected to inspection
with a blacklight, a crack will glow brightly. Developing solution
is often used to enhance results. Parts made of any material, such as
aluminum cylinder heads or plastics, may be tested using this process.
Dye Check
Penetrating dye is sprayed on the previously cleaned
component. Dye is left on component for 5-45 minutes, depending upon
material density. Component is then wiped clean and sprayed with a
developing solution. Surface cracks will show up as a bright line.
ULTRASONIC INSPECTION
If an expensive part is suspected of internal cracking,
Ultrasonic testing is used. Sound waves are used for component
inspection.
X-RAY INSPECTION
This form of inspection is used on highly stressed
components. X-ray inspection maybe used to detect internal and
external flaws in any material.
PRESSURE TESTING
Cylinder heads can be tested for cracks using a pressure
tester. Pressure testing is performed by plugging all but one of the
holes in the head and injecting air or water into the open passage.
Leaks are indicated by the appearance of wet or damp areas when using
water. When air is used, it is necessary to spray the head surface
with a soap solution. Bubbles will indicate a leak. Cylinder head may
also be submerged in water heated to specified temperature to check
for cracks created during heat expansion.
CLEANING PROCEDURES
* PLEASE READ THIS FIRST *
NOTE: Always refer to appropriate engine overhaul article in the
ENGINES section for complete overhaul procedures and
specifications for the vehicle being repaired.
GENERAL
All components of an engine do not have the same cleaning
requirements. Physical methods include bead blasting and manual
removal. Chemical methods include solvent blast, solvent tank, hot
tank, cold tank and steam cleaning of components.
BEAD BLASTING
Manual removal of deposits may be required prior to bead
blasting, followed by some other cleaning method. Carbon, paint and

rust may be removed using bead blasting method. Components must be
free of oil and grease prior to bead blasting. Beads will stick to
grease or oil soaked areas causing area not to be cleaned.
Use air pressure to remove all trapped residual beads from
components after cleaning. After cleaning internal engine parts made
of aluminum, wash thoroughly with hot soapy water. Component must be
thoroughly cleaned as glass beads will enter engine oil resulting in
bearing damage.
CHEMICAL CLEANING
Solvent tank is used for cleaning oily residue from
components. Solvent blasting sprays solvent through a siphon gun using
compressed air.
The hot tank, using heated caustic solvents, is used for
cleaning ferrous materials only. DO NOT clean aluminum parts such as
cylinder heads, bearings or other soft metals using the hot tank.
After cleaning, flush parts with hot water.
A non-ferrous part will be ruined and caustic solution will
be diluted if placed in the hot tank. Always use eye protection and
gloves when using the hot tank.
Use of a cold tank is for cleaning of aluminum cylinder
heads, carburetors and other soft metals. A less caustic and unheated
solution is used. Parts may be lift in the tank for several hours
without damage. After cleaning, flush parts with hot water.
Steam cleaning, with boiling hot water sprayed at high
pressure, is recommended as the final cleaning process when using
either hot or cold tank cleaning.
COMPONENT CLEANING
* PLEASE READ THIS FIRST *
NOTE: Always refer to appropriate engine overhaul article in the
ENGINES section for complete overhaul procedures and
specifications for the vehicle being repaired.
SHEET METAL PARTS
Examples of sheet metal parts are the rocker covers, front
and side covers, oil pan and bellhousing dust cover. Glass bead
blasting or hot tank may be used for cleaning.
Ensure all mating surfaces are flat. Deformed surfaces should
be straightened. Check all sheet metal parts for cracks and dents.
INTAKE & EXHAUST MANIFOLDS
Using solvent cleaning or bead blasting, clean manifolds for
inspection. If the intake manifold has an exhaust crossover, all
carbon deposits must be removed. Inspect manifolds for cracks, burned
or eroded areas, corrosion and damage to fasteners.
Exhaust heat and products of combustion cause threads of
fasteners to corrode. Replace studs and bolts as necessary. On "V"
type intake manifolds, the sheet metal oil shield must be removed for
proper cleaning and inspection. Ensure that all manifold parting
surfaces are flat and free of burrs.
CYLINDER HEAD REPLACEMENT
* PLEASE READ THIS FIRST *

NOTE: Always refer to appropriate engine overhaul article in the
ENGINES section for complete overhaul procedures and
specifications for the vehicle being repaired.
REMOVAL
Remove intake and exhaust manifolds and valve cover. Cylinder
head and camshaft carrier bolts (if equipped), should be removed only
when the engine is cold. On many aluminum cylinder heads, removal
while hot will cause cylinder head warpage. Mark rocker arm or
overhead cam components for location.
Remove rocker arm components or overhead cam components.
Components must be installed in original location. Individual design
rocker arms may utilize shafts, ball-type pedestal mounts or no rocker
arms. For all design types, wire components together and identify
according to the corresponding valve. Remove cylinder head bolts.
Note length and location. Some applications require cylinder head
bolts be removed in proper sequence to prevent cylinder head damage.
See Fig. 1 . Remove cylinder head.
Fig. 1: Typical Cylinder Head Tightening or Loosening Sequence
This Graphic For General Information Only
INSTALLATION
Ensure all surfaces and head bolts are clean. Check that head
bolt holes of cylinder block are clean and dry to prevent block damage
when bolts are tightened. Clean threads with tap to ensure accurate
bolt torque.
Install head gasket on cylinder block. Some manufacturer's
may recommend sealant be applied to head gasket prior to installation.
Note that all holes are aligned. Some gasket applications may be
marked so certain area faces upward. Install cylinder head using care
not to damage head gasket. Ensure cylinder head is fully seated on
cylinder block.
Some applications require head bolts be coated with sealant
prior to installation. This is done if head bolts are exposed to water
passages. Some applications require head bolts be coated with light
coat of engine oil.