1991 MITSUBISHI MONTERO check engine

2.0L .............................. Yellow/Red ............. (5)\
Montero
3.0L ............................. White/Yellow ............ (4)\
Pickup & Ram-50
2.4L .............................. Black/Blue ............. (6)\
3.0L ............................. White/Yellow ............ (6)\
Stealth (SOHC)
3.0L ............................. White/Yellow ............ (4)\
Stealth & 3000GT (DOHC)
3.0L (Non-Turbo) ................. Black/Green ............. (4\
)
3.0L (Turbo) ..................... White/Yellow ............ (4\
)
(1) - Remove waterproof female connector (if equipped) for access to\
wire.
(2) - Ground connector at wire end for basic timing adjustment.
(3) - On main wiring harness, near center of firewall.
(4) - On main wiring harness, near wiper motor on firewall.
(5) - On main wiring harness, near master cylinder on firewall.
(6) - Between right shock tower and firewall.
(7) - Near front of right shock tower.









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IDLE SPEED & MIXTURE
NOTE: Perform adjustments with engine at normal operating
temperature, cooling fan and accessories off, transmission
in Park or Neutral, and front wheels in straight-ahead
position.
CURB (SLOW) IDLE SPEED
NOTE: Curb idle speed is controlled by Idle Speed Control (ISC)
motor. Adjustment is usually not necessary. For curb idle
speed specifications, see IDLE SPEED SPECIFICATIONS table
under BASIC IDLE SPEED.
1) Check ignition timing and adjust if necessary. Run engine
at 2000-3000 RPM for more than 5 seconds. Allow engine to idle for 2
minutes. Check curb idle speed.
2) If curb idle speed is not within specification, check ISC
system. If ISC system is okay, adjust basic idle speed. See BASIC IDLE
SPEED.
BASIC IDLE SPEED
NOTE: ALWAYS check TPS adjustment after adjusting basic idle
speed. See THROTTLE POSITION SENSOR (TPS).
BASIC IDLE SPEED TEST APPLICATION TABLE









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Application Test
1.5L
Colt, Colt 200,
Mirage & Summit ............. TEST NO. 1
1.6L
Mirage ....................... TEST NO. 2
1.8L
Eclipse ...................... TEST NO. 1
2.0L (VIN V)
Colt Vista & Galant .......... TEST NO. 1
2.0L (VIN R & U)

Eclipse & Galant ............. TEST NO. 2
2.4L
Pickup & Ram-50 .............. TEST NO. 1
3.0L
Montero, Pickup, Ram-50,
Stealth & 3000GT ............ TEST NO. 2









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Test No. 1
1) Loosen throttle cable. Turn ignition on for more than 15
seconds. DO NOT start engine. Turn ignition off. This should fully
retract ISC motor plunger.
2) On 2.0L Galant (VIN V), connect jumper wire between
ignition timing adjustment connector and ground. See IGNITION TIMING
ADJUSTMENT CONNECTOR LOCATION table under IGNITION TIMING.
3) On all models, disconnect harness connector(s) from Idle
Speed Control (ISC) motor. Ensure ISC plunger is in fully retracted
position. Unscrew fixed Speed Adjusting Screw (SAS) until throttle
valve is fully closed. See Fig. 1.
CAUTION: When cleaning throttle body, plug air by-pass hole in
throttle body to prevent solvent from entering passage.
4) Start engine. Check basic idle speed. See IDLE SPEED
SPECIFICATIONS table. If basic idle speed is within specification, go
to step 7). If basic idle speed is not within specification, remove
air intake hose and clean throttle body. Reconnect air intake hose.
Recheck basic idle speed.
5) If basic idle speed is still not within specification
after cleaning throttle body, adjust basic idle speed by turning idle
speed adjusting screw. See Fig. 1. After adjusting basic idle speed,
turn fixed SAS screw clockwise until engine speed begins to increase.
6) Turn fixed SAS screw counterclockwise until engine speed
decreases. Turn fixed SAS screw counterclockwise an additional 1/2
turn from point at which engine speed no longer decreases. Turn off
engine.
7) Adjust throttle cable. Reconnect harness connector(s) at
ISC motor. Start engine. Operate engine for about 5 minutes. Ensure
engine idles within curb idle speed specification. See IDLE SPEED
SPECIFICATIONS table.
8) Turn ignition off. Disconnect negative battery cable for
at least 10 seconds to clear diagnostic trouble code. Reconnect
negative battery cable. Operate engine at idle for about 5 minutes to
ensure engine idles smoothly.
Test No. 2
1) Locate ignition timing adjustment connector. See IGNITION
TIMING ADJUSTMENT CONNECTOR LOCATION table under IGNITION TIMING.
Connect jumper wire between ignition timing adjustment connector and
ground.
2) Locate diagnostic connector under instrument panel.
Connect jumper wire between diagnostic connector terminal No. 10
(White wire) and ground. See Fig. 3. Start engine. Check basic idle
speed. See IDLE SPEED SPECIFICATIONS table. If basic idle speed is
within specification, go to step 9). If basic idle speed is not within
specification, go to step 3).
3) Remove air intake hose. Check throttle body. If throttle
body contains deposits, go to next step. If throttle body is clean,
disconnect jumper wires connected in steps 1) and 2). On all models
except Eclipse, Galant and Mirage, go to step 6). On Eclipse, Galant
and Mirage, go to step 5).
CAUTION: When cleaning throttle body, plug air by-pass hole in

throttle body to prevent solvent from entering passage.
4) Clean throttle body with solvent. Replace air intake hose.
Recheck basic idle speed. If basic idle speed is within specification
after cleaning throttle body, go to step 9). If basic idle speed is
still not within specification after cleaning throttle body,
disconnect jumper wires connected in steps 1) and 2). On all models
except Eclipse, Galant and Mirage, go to step 6). On Eclipse, Galant
and Mirage, go to step 5).
5) Adjust idle position switch and go to step 7). See IDLE
POSITION SWITCH under THROTTLE POSITION SENSOR (TPS).
6) Adjust fixed Speed Adjusting Screw (SAS) and go to next
step. See FIXED SPEED ADJUSTING SCREW under IDLE SPEED & MIXTURE.
7) Reconnect jumper wires as indicated in steps 1) and 2).
Check basic idle speed. If basic idle speed is within specification,
go to step 9). If basic idle speed is not within specification, adjust
by turning idle speed adjusting screw on throttle body. See Fig. 2. Go
to next step.
8) If basic idle speed is within specification after turning
idle speed adjusting screw, go to step 9). If basic idle speed cannot
be adjusted to specification by turning idle speed adjusting screw,
check for leaking fast idle air valve. Replace throttle body if fast
idle air valve leaks.
9) Turn ignition off. Disconnect jumper wires from ignition
timing adjustment connector and diagnostic connector. Operate engine
at idle for about 5 minutes. Ensure engine idles smoothly and within
curb idle specification. See IDLE SPEED SPECIFICATIONS table.
IDLE SPEED SPECIFICATIONS TABLE









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Application Curb Idle Basic Idle
1.5L
Colt, Colt 200,
Mirage & Summit .... 650-850 ...... 700-800
1.6L
Mirage .............. 650-850 ...... 700-800
1.8L
Eclipse ............. 600-800 ...... 650-750
2.0L (VIN V)
Colt Vista .......... 600-800 ...... 650-750
Galant .............. 650-850 ...... 700-800
2.0L (VIN R & U)
Eclipse ............. 650-850 ...... 650-750
Galant .............. 650-850 ...... 700-800
2.4L
Pickup & Ram-50 ..... 650-850 ...... 700-800
3.0L
Montero, Pickup, Ram-50,
Stealth & 3000GT . 600-800 ...... 650-750









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Fig. 1: Idle & Fixed Speed Adj. Screws (1.5L, 1.8L, 2.0L (VIN V)
& 2.4L)

cable. Using digital voltmeter, backprobe terminal No. 19 (Green/White
wire) and terminal No. 24 (Black or Green/Black wire) at Engine
Control Unit (ECU) wiring harness connector. Check TPS output voltage.\
2) If output voltage is .48-.52 volt, go to step 3). If
output voltage is not .48-.52 volt, remove throttle body. Loosen TPS
mounting screws and rotate TPS clockwise, or counterclockwise, until
output voltage is within specification. Tighten TPS mounting screws.
3) Turn ignition off. Disconnect voltmeter from ECU harness
connector. Adjust throttle cable. Disconnect negative battery cable
for at least 10 seconds to clear diagnostic code. Reconnect negative
battery cable. Operate engine at idle for about 5 minutes to ensure
engine idles smoothly.
Test No. 3
1) Turn ignition on for more than 15 seconds. DO NOT start
engine. Turn ignition off. This should fully retract ISC plunger.
2) Ensure ISC plunger is fully retracted. Disconnect TPS
harness connectors. Connect Test Harness (MD998474) between
connectors. Connect digital voltmeter between Red and Blue wires of
test harness.
3) Turn ignition on. DO NOT start engine. TPS voltage should
be .48-.52 volt. If TPS voltage is .48-.52 volt, go to step 4). If TPS
voltage is not .48-.52 volt, loosen TPS mounting screws and rotate TPS
clockwise, or counterclockwise, until correct voltage is obtained.
Tighten TPS mounting screws.
4) Turn ignition off. Disconnect voltmeter and remove test
harness. Reconnect TPS harness connectors. Adjust throttle cable.
Start engine and check idle speed.
5) Turn ignition off. Disconnect negative battery cable for
at least 10 seconds to clear diagnostic trouble code. Reconnect
negative battery cable. Operate engine at idle for about 5 minutes to
ensure engine idles smoothly.
Test No. 4
1) Loosen throttle cable. Disconnect electrical connector
from TPS. Connect digital ohmmeter between Green/White and
Green/Yellow wire terminals of TPS electrical connector (on TPS side
of harness).
2) Insert .026" (.66 mm) feeler gauge between fixed Speed
Adjusting Screw (SAS) and throttle lever. See Fig. 4. Loosen TPS
mounting screws. Rotate TPS fully clockwise. Check for continuity
between Green/White wire and Green/Yellow wire terminals of TPS
electrical connector.
3) Rotate TPS counterclockwise until ohmmeter registers no
continuity. Tighten TPS mounting screws and reconnect TPS electrical
connector.
4) Using digital voltmeter, backprobe terminal No. 19
(Green/White wire) and terminal No. 24 (Black or Green/Black wire) a\
t
Engine Control Unit (ECU) wiring harness connector. Turn ignition on.
DO NOT start engine. Check TPS output voltage.
5) If TPS output voltage is 0.4-1.0 volt, go to step 6). If
TPS output voltage is not 0.4-1.0 volt, check TPS and wiring harness
for damage or malfunction. Replace TPS or repair wiring harness if
necessary and go to next step.
6) Remove feeler gauge. Turn ignition off. Disconnect
voltmeter from ECU connector. Adjust throttle cable. Operate engine at
idle for about 5 minutes to ensure engine idles smoothly and within
specification.
Test No. 5
1) Disconnect electrical connector from TPS. Connect digital
ohmmeter between Yellow/Red wire and Black wire terminals of TPS.
2) Insert .026" (.66 mm) feeler gauge between fixed Speed

Adjusting Screw (SAS) and throttle lever. See Fig. 4. Loosen TPS
mounting screws. Rotate TPS fully counterclockwise. Check for
continuity between Yellow/Red wire and Black wire terminals of TPS.
3) Rotate TPS clockwise until ohmmeter registers no
continuity. Tighten TPS mounting screws. Reconnect TPS electrical
connector.
4) Use a digital voltmeter to backprobe terminal No. 19
(Brown/Red wire) and terminal No. 24 (Brown wire) at Engine Control
Unit (ECU) wiring harness on SOHC vehicles, or terminal No. 64
(Brown/Red wire) and terminal No. 72 (Black wire) on DOHC vehicles.
Turn ignition on. DO NOT start engine. Check TPS output voltage.
5) If TPS output voltage is 0.4-1.0 volt, go to step 6). If
TPS output voltage is not 0.4-1.0 volt, check TPS and wiring harness
for damage or malfunction. Replace TPS or repair wiring harness if
necessary and go to step 6).
6) Remove feeler gauge. Turn ignition off. Disconnect
voltmeter from ECU connector. Operate engine at idle for about 5
minutes to ensure engine idles smoothly and within specification.
IDLE POSITION SWITCH
NOTE: Idle position switch is preset by manufacturer. Adjustment
is usually not necessary. If other procedures in this
article require adjustment of idle position switch or if
switch setting has been changed, adjust switch as follows.
1.6L Mirage, 2.0L Eclipse & 2.0L Galant (DOHC)
1) Loosen throttle cable. Disconnect electrical connector
from idle position switch. See Fig. 5. Loosen lock nut at base of
switch. Turn switch counterclockwise until throttle valve is fully
closed.
2) Connect ohmmeter between switch terminal and switch body
(ground). Turn idle position switch clockwise until ohmmeter registers\
continuity. At this point, throttle valve should begin to open.
3) Turn switch 15/16 of a turn beyond contact point. Tighten
lock nut at base of idle position switch, holding switch to prevent it
from turning while tightening.
4) Adjust throttle cable. Adjust basic idle speed. See BASIC
IDLE SPEED. Adjust TPS. See TPS ADJUSTMENT.
All Other Models
Idle position switch is incorporated in ISC motor and is
automatically adjusted when TPS is adjusted. See TPS ADJUSTMENT.
Fig. 5: Idle Position Switch Location (1.6L & 2.0L (VIN R &U))
Courtesy of Mitsubishi Motor Sales of America.

terminal "B" and negative lead to positive battery terminal. Reconnect
negative battery cable.
3) Start engine. Turn accessories on and adjust engine speed
until ammeter indicates 20 amps, and note voltmeter reading. If
voltmeter indicates .2 volt or less, system is okay.
4) If voltage is greater than .2 volt, wiring is defective
between alternator terminal "B", fusible link and battery positive
terminal. Disconnect negative battery cable, and remove test
equipment.
ALTERNATOR OUTPUT TEST
NOTE: During alternator output test, a slightly discharged battery
should be used as a fully charged battery may not allow full
alternator output.
1) Turn ignition switch to OFF position. Disconnect negative
battery cable. Disconnect alternator output wire from terminal "B".
Install positive lead of 100-amp ammeter to terminal "B" and negative
lead to disconnected output lead.
CAUTION: Tighten each connection securely as heavy current flow will
exist. DO NOT use clips on ammeter.
2) Connect positive voltmeter lead (0-20 volts) to alternato\
r
terminal "B" and negative lead to ground. Install tachometer, and
reconnect negative battery cable.
3) Ensure voltmeter indicates battery voltage. If no voltage
exists, an open circuit is present in wire between alternator terminal
"B" and battery negative terminal. Check grounds and fusible link.
4) Turn headlights on, and start engine. Set headlights at
high beam and heater switch on HIGH. Quickly accelerate engine speed
to 2500 RPM and note alternator output current registered on the
ammeter. Minimum output should be within specification. Refer to the
ALTERNATOR MINIMUM OUTPUT SPECIFICATIONS table.
NOTE: Output voltage changes with electrical load and temperature.
Ensure proper electrical load is applied while checking
output. Nominal output may not be obtained if alternator or
ambient temperature is excessive. Allow to cool, and recheck
output. Alternator output is stamped on metal plate attached
to alternator case.
5) If minimum output is not obtained and alternator wiring is
okay, repair alternator. Disconnect negative battery cable, and remove
test equipment.
REGULATED VOLTAGE TEST
NOTE: Ensure battery is fully charged and proper drive belt
tension exists.
1) Turn ignition switch to OFF position. Disconnect negative
battery cable. Install a digital voltmeter between alternator terminal
"S" and ground. See Fig. 10. Connect positive voltmeter lead to
terminal "S" of alternator. Connect negative voltmeter lead to ground.
2) Disconnect alternator output wire from terminal "B".
Install a 100-amp ammeter in series to terminal "B" and disconnected
output lead. Install positive lead of ammeter to terminal "B" and
negative lead to disconnected output wire. Install a tachometer, and
reconnect negative battery cable.
3) Turn ignition switch to ON position and ensure voltmeter
indicates battery voltage. If no voltage exists, an open circuit

exists in wire between alternator terminal "S" and positive battery
terminal or fusible link is blown.
4) Start engine. Ensure all lights and accessories are off.
Operate engine at 2500 RPM and read voltmeter when alternator output
current drops to 10 amps or less. Voltage regulator is okay if voltage
output is within specification. See REGULATOR VOLTAGE SPECIFICATIONS
table.
BENCH TESTING
RECTIFIER ASSEMBLY
1) Using ohmmeter, check for continuity between both diodes
and stator coil lead connection. See Fig. 11. Reverse leads. If
continuity exists in both directions, diode is shorted. Replace
rectifier assembly.
2) To check entire diode assembly, use an ohmmeter to check
for continuity between both ends of each diode. See Fig. 11. Switch
ohmmeter leads. Continuity should exist in one direction, but not
other. If no continuity exists or continuity exists in both
directions, diode is defective. Replace rectifier assembly.
Fig. 11: Testing Rectifier Assembly
Courtesy of Mitsubishi Motor Sales of America.
ROTOR

\003
F - B ASIC T E STIN G

1991 M it s u bis h i M onte ro
1991 ENGINE PERFORMANCE
Basic Diagnostic Procedures
Chrysler; Colt, Colt 200, Colt Vista, Ram-50, Stealth,
Summit
Mitsubishi; Eclipse, Galant, Mirage, Montero, Pickup, 3000GT
INTRODUCTION
The following diagnostic steps will help prevent overlooking
a simple problem. This is also where to begin diagnosis for a no start
condition. First step in diagnosing any driveability problem is
verifying customer's complaint with a test drive under conditions
problem reportedly occurred.
Before entering self-diagnostics, perform a careful and
complete visual inspection. Most engine control problems result from
mechanical breakdowns, poor electrical connections or
damaged/misrouted vacuum hoses. Before condemning computerized system,
perform each test listed in article.
NOTE: Perform all voltage tests with a Digital Volt-Ohmmeter (DVOM)\
with a minimum 10-megohm input impedance, unless stated
otherwise in test procedure.
PRELIMINARY INSPECTION & ADJUSTMENTS
VISUAL INSPECTION
Visually inspect all electrical wiring, looking for chafed,
stretched, cut or pinched wiring. Ensure electrical connectors fit
tightly and are not corroded. Ensure distributor cap and rotor are
free of cracks, carbon trails or contamination. Ensure vacuum hoses
are properly routed and not pinched or cut. See M - VACUUM DIAGRAMS
article in the ENGINE PERFORMANCE Section to verify routing and
connections (if necessary). Inspect air induction system for possible
vacuum leaks.
MECHANICAL INSPECTION
Compression
Check engine mechanical condition with a compression gauge,
vacuum gauge, or an engine analyzer. See engine analyzer manual for
specific instructions.
WARNING: DO NOT use ignition switch during compression tests. Use a
remote starter to crank engine. Fuel injectors on many models
are triggered by ignition switch during cranking mode, which
can create a fire hazard or contaminate engine's oiling
system.
COMPRESSION SPECIFICATIONS TABLE (1)









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Application Specification
psi (kg/cm)
1.5L (VIN X) .............................. 137 (9.6)
1.6L (VIN Y) ............................. 171 (12.0)
1.8L (VIN T) .............................. 131 (9.2)