check engine MITSUBISHI MONTERO 1991 Service Manual

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G - T E STS W /C O DES
1991 Mitsubishi Montero
1990-91 ENGINE PERFORMANCE
Chrysler Motors/Mitsubishi Self-Diagnostics
Dodge; Colt, Colt Vista, Colt Wagon
Eagle; Summit
Mitsubishi; Eclipse, Galant, Mirage, Montero, Precis (1990)
Plymouth; Colt, Colt Vista, Colt Wagon
INTRODUCTION
If no faults were found while performing F - BASIC TESTING,
proceed with self-diagnostics. If no fault codes or only pass codes
are present after entering self-diagnostics, proceed to H - TESTS W/O
CODES article for diagnosis by symptom (i.e. ROUGH IDLE, NO START,
etc.).
SELF-DIAGNOSTIC SYSTEM
Use Chrysler Motors code charts when using Chrysler's
Diagnostic Readout Box (DRB-II). If DRB-II is not available or if
working on a Mitsubishi Motors vehicle, system diagnosis can only be
accomplished using a voltmeter or appropriate scan tester. To diagnose
Chrysler Motors and Mitsubishi models using a voltmeter, see
ENTERING ON-BOARD DIAGNOSTICS (USING VOLTMETER) in this article.
SYSTEM DIAGNOSIS
SYSTEM DIAGNOSIS DESCRIPTION
NOTE: Chrysler Motors recommends using DRB-II to diagnose system.
Voltmeter usage has limited diagnostic capabilities but can
be used if DRB-II is not available or if working on a
Mitsubishi Motors vehicle.
The Engine Control Unit (ECU) monitors several different
engine control system circuits. If an abnormal input signal occurs, a
fault code is stored in ECU memory and given a fault code number. Each
circuit has its own fault number and message. A specific fault code
indicates a particular system failure, but it DOES NOT indicate that
cause of failure is necessarily within system. A fault code DOES NOT
condemn any specific component; it simply points out a probable
malfunctioning area. If a critical fault code is set, the ECU will
turn on CHECK ENGINE light. All fault codes except speed sensor are
considered critical.
Fault codes can be confirmed by using a voltmeter on Chrysler
Motors and Mitsubishi models or Chrysler's Diagnostic Readout Box
(DRB-II) on Chrysler Motors vehicles. See
ENTERING ON-BOARD DIAGNOSTICS (USING VOLTMETER) or ENTERING ON-BOARD
DIAGNOSTICS (USING DRB-II) in this article. By using the DRB-II, the
self-diagnostic capabilities of this system can simplify testing and
reduce diagnostic time.
System malfunctions encountered are identified as either hard
failures or intermittent failures as determined by the ECU.
HARD FAILURES
Hard failures cause CHECK ENGINE light to illuminate and
remain on until the malfunction is repaired. If light comes on and

remains on (light may flash) during vehicle operation, cause of
malfunction must be determined by using DIAGNOSTIC FAULT CHARTS (if
testing with voltmeter) or diagnostic CODE CHARTS (if testing with
DRB-II). If a sensor fails, ECU will use a substitute value in its
calculations to continue engine operation. In this condition, vehicle
is functional, but loss of good driveability may result.
INTERMITTENT FAILURES
Intermittent failures may cause CHECK ENGINE light to flicker
or illuminate and go out after the intermittent fault goes away.
However, the corresponding trouble code will be retained in ECU
memory. If related fault does not reoccur within a certain time frame,
related trouble code will be erased from ECU memory. Intermittent
failures may be caused by a sensor, connector or wiring related
problems. See INTERMITTENTS in H - TESTS W/O CODES article.
PRETEST INSPECTION
Before proceeding with diagnosis, the following precautions
must be followed:
* Vehicle must have a fully charged battery and functional
charging system.
* Visually inspect connectors and circuit wiring being worked
on.
* DO NOT disconnect battery or ECU. This will erase any fault
codes stored in ECU.
* DO NOT cause short circuits when performing electrical tests.
This will set additional fault codes, making diagnosis of original
problem more difficult.
* DO NOT use a test light in place of a voltmeter.
* When checking for spark, ensure coil wire is NO more than
1/4" from ground. If coil wire is more than 1/4" from ground,
damage to vehicle electronics and/or ECU may result.
* DO NOT prolong testing of fuel injectors. Engine may
hydrostatically (liquid) lock.
* When a vehicle has multiple fault codes, always repair lowest
number fault code first.
* If DRB-II is being used to diagnose system, always perform
verification test after repairs are made.
ENTERING ON-BOARD DIAGNOSTICS (USING VOLTMETER)
1) Before entering on-board diagnostics, refer to PRETEST
INSPECTION in this article. Turn ignition switch to OFF position.
Locate self-diagnostic connector. See SELF-DIAGNOSTIC TEST CONNECTOR
LOCATION table. Using an analog voltmeter, connect voltmeter positive
lead to self-diagnostic connector terminal No. 1 and negative lead to
terminal No. 12 (ground). See Fig. 6.
2) Turn ignition switch to ON position and disclosure of ECU
memory will begin. If 2 or more systems are non-functional, they are
indicated by order of increasing code number. Indication is made by
12-volt pulses of voltmeter pointer. A constant repetition of short
12-volt pulses indicates system is normal. If system is abnormal,
voltmeter will pulse between zero and 12 volts.
3) Signals will appear on voltmeter as long and short 12-volt
pulses. Long pulses represent tens; short pulses represent ones. For
example 4 long pulses and 3 short pulses indicates Code 43. See

Fig. 2: Diagnostic Fault Chart (2 of 2)
Courtesy of Mitsubishi Motor Sales of America.
DIAGNOSTIC PROCEDURE (USING DRB-II)
DRB-II PROCEDURE
NOTE: When using diagnostic code charts, DO NOT skip any steps in
chart or incorrect diagnosis may result. Always check related
Technical Service Bulletins (TSB's).
Refer to ENTERING ON-BOARD DIAGNOSTICS (USING DRB-II) to
retrieve fault codes. If fault codes are NOT present and/or DRB-II is
used, proceed to one of the following tests:
* Go to NO START TEST 1 (NS-1) chart if a no-start condition
exists or engine stalls after start-up. Perform indicated
VERIFICATION PROCEDURE chart after repairs. Ensure charts
apply to engine being tested.
* Go to DRIVEABILITY TEST 1 (DR-1) chart if engine runs but has
performance problems. Perform indicated VERIFICATION

44 (5) ..... Open or short in either ignition coil circuit
( 1) - Except Montero & Sigma.
( 2) - Will not turn on CHECK ENGINE light.
( 3) - 2.0L turbo only.
( 4) - California only. Except Sigma.
( 5) - Chrysler Motors models only.









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CLEARING CODES
Using DRB-II, from main menu select ADJUSTMENTS. Enter ERASE
FAULTS. Follow DRB-II instructions to accomplish this task. If DRB-II
is not available, fault codes may be cleared by disconnecting negative
battery cable for at least 10 seconds, allowing ECU to clear fault
codes.
TEST CHARTS
* PLEASE READ THIS FIRST *
NOTE: The following charts are supplied for Chrysler Motors
vehicles.
NS-1: TESTING IGNITION CIRCUIT - 1.5L
Fig. 7: Circuit Diagram NS-1 (1.5L) (1 of 2)
Fig. 8: Circuit Diagram NS-1 (1.5L) (2 of 2)

that all of the engine control systems are operating as they were
designed to. Therefore, they are not the cause of the driveability
problem.
The following additional items can not be overlooked as possible
causes of a driveability problem.
1. THROTTLE VALVE AREA - Dirt or ice buildup causing rough idle and
stalling.
2. ENGINE IGNITION TIMING - Must be set with timing terminal
grounded.
3. ENGINE VACUUM - Must be normal for your altitude.
4. ENGINE VALVE TIMING - To specifications.
5. ENGINE COMPRESSION - To specifications.
6. ENGINE P.C.V. SYSTEM - Must flow freely.
7. ENGINE EXHAUST SYSTEM - Must be free of any restrictions.
8. POWER BRAKE BOOSTER - No internal vacuum leaks.
9. TORQUE CONVERTER CONDITION - May cause very low power at breakaway
or high speed (Only 1 condition at a time).
10. FUEL CONTAMINATION - High alcohol or water content.
11. FUEL INJECTORS - Rough idle may be caused by injector wiring not
connected to correct injector.
12. ENGINE SECONDARY IGNITION CHECK - Abnormal scope patterns.
13. TECHNICAL SERVICE BULLETINS - Any that apply to vehicle.
14. All air intake piping and vacuum hoses must be in place and
secure. The proper air filter element must be used.
15. FUEL PRESSURE - Must be correct.
Specification: With no vacuum at the regulator:
48 PSI on V6 & non-turbo 4 Cyl. engines
36 PSI on turbo engines
NS-1: TESTING IGNITION CIRCUIT - 1.6L
Fig. 75: Circuit Diagram NS-1 (1.6L)

The following additional items can not be overlooked as
possible causes of a driveability problem.
1. ENGINE IGNITION TIMING - Must be set with timing terminal
grounded.
2. ENGINE VACUUM - Must be normal for your altitude.
3. ENGINE VALVE TIMING - To specifications.
4. ENGINE COMPRESSION - To specifications.
5. ENGINE P.C.V. SYSTEM - Must flow freely.
6. ENGINE EXHAUST SYSTEM - Must be free of any restrictions.
7. POWER BRAKE BOOSTER - No internal vacuum leaks.
8. TORQUE CONVERTER CONDITION - May cause very low power at breakaway
or high speed (Only 1 condition at a time).
9. FUEL CONTAMINATION - High alcohol or water content.
10. FUEL INJECTORS - Rough idle may be caused by injector wiring not
connected to correct injector.
11. ENGINE SECONDARY IGNITION CHECK - Abnormal scope patterns.
12. TECHNICAL SERVICE BULLETINS - Any that apply to vehicle.
13. All air intake piping and vacuum hoses must be in place and
secure. The proper air filter element must be used.
14. FUEL PRESSURE - Must be correct.
Specification: With no vacuum at the regulator:
48 PSI on V6 & non-turbo 4 Cyl. engines
36 PSI on turbo engines
NS-VER: NO START VERIFICATION PROCEDURE - 1.6L
Fig. 168: Flow Chart NS-VER (1.6L)
DR-VER: DRIVEABILITY VERIFICATION PROCEDURE - 1.6L

2. ENGINE IGNITION TIMING - Must be set with timing terminal
grounded.
3. ENGINE VACUUM - Must be normal for your altitude.
4. ENGINE VALVE TIMING - To specifications.
5. ENGINE COMPRESSION - To specifications.
6. ENGINE P.C.V. SYSTEM - Must flow freely.
7. ENGINE EXHAUST SYSTEM - Must be free of any restrictions.
8. POWER BRAKE BOOSTER - No internal vacuum leaks.
9. TORQUE CONVERTER CONDITION - May cause very low power at breakaway
or high speed (Only 1 condition at a time).
10. FUEL CONTAMINATION - High alcohol or water content.
11. FUEL INJECTORS - Rough idle may be caused by injector wiring not
connected to correct injector.
12. ENGINE SECONDARY IGNITION CHECK - Abnormal scope patterns.
13. TECHNICAL SERVICE BULLETINS - Any that apply to vehicle.
14. All air intake piping and vacuum hoses must be in place and
secure. The proper air filter element must be used.
15. FUEL PRESSURE - Must be correct.
Specification: With no vacuum at the regulator:
48 PSI on V6 & non-turbo 4 Cyl. engines
36 PSI on turbo engines
NS-1: IGNITION CHECK FLOW CHARTS - 2.0L
Fig. 235: NS-1 Flow Chart & Circuit Diagram (2.0L) (1 of 5)

determined that all of the engine controls systems are operating as
they were designed to. Therefore, they are not the cause of the
driveability problem. The following additional items should be checked
as possible causes:
1) ENGINE VACUUM - Must be at least 13 inches in neutral.
2) ENGINE VALVE TIMING - Set to specifications.
3) ENGINE COMPRESSION - To specifications.
4) EXHAUST SYSTEM - Free from any restrictions.
5) PCV SYSTEM - Must flow freely.
6) DRIVE SPROCKETS - Camshaft and crank shaft.
7) TORQUE CONVERTER STALL SPEED - To specifications.
8) POWER BRAKE BOOSTER - No internal vacuum leak.
9) FUEL CONTAMINATION - High alcohol and water content.
10) FUEL INJECTORS - Rough idle may be caused by injector
control wire not connected to correct injector.
11) TECHNICAL SERVICE BULLETINS - Any that may apply to
vehicle.
12) ENGINE SECONDARY IGNITION CHECK - Any abnormal scope
pattern.
13) TECHNICAL SERVICE BULLETINS - Any that apply to vehicle.
14) All air intake piping and vacuum hoses must be in place
and secure. The proper air filter element must be used.
15) FUEL PRESSURE - Must be correct.
Specification: With no vacuum at the regulator:
48 PSI on V6 & non-turbo 4 Cyl. engines
36 PSI on turbo engines
DR-VER: DRIVEABILITY VERIFICATION TEST - 2.0L
Fig. 300: DR-VER Flow Chart (2.0L)
SUMMARY

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H - T E STS W /O C O DES

1991 M it s u bis h i M onte ro
1991 ENGINE PERFORMANCE
Trouble Shooting - No Codes
Chrysler Motors: Colt, Colt 200, Colt Vista, Ram-50, Stealth,
Summit,
Mitsubishi: Eclipse, Galant, Mirage, Montero, Pickup, 3000GT
INTRODUCTION
Before diagnosing symptoms or intermittent faults, perform
steps in F - BASIC TESTING and G - TESTS W/ CODES articles in the
ENGINE PERFORMANCE Section. Use this article to diagnose driveability
problems that exist when a hard fault code is NOT found, or on vehicle
NOT equipped with a self-diagnostic system.
NOTE: Computer control unit has been revised to correct certain
driveability problems. Check with manufacturer for latest
computer application.
Symptom checks are intended to direct technician to
malfunctioning component(s) so further diagnosis may be performed. A
symptom should lead to specific component or system testing, or an
adjustment specification.
Use intermittent test procedures to locate driveability
problems that DO NOT occur when vehicle is being tested. These test
procedures should also be used if a soft (intermittent) trouble code
was present, but no problem was found during self-diagnostic testing.
NOTE: For specific testing procedures, see I - SYS/COMP TESTS
article in the ENGINE PERFORMANCE Section. For
specifications, see C - SPECIFICATIONS or D - ADJUSTMENTS
article in the ENGINE PERFORMANCE Section.
SYMPTOMS
SYMPTOM DIAGNOSIS
Symptom checks cannot be used unless problem occurs while
vehicle is being tested. Symptoms available for diagnosis include the
following:
* Difficult to start/no start (cranks okay)
* Rough or unstable idle
* Engine hesitates or poor acceleration
* Engine surges
* Detonation or knocking
* Poor fuel mileage
SYMPTOMS (PFI)
DIFFICULT TO START/NO START (CRANKS OKAY)
* Check idle speed control servo (if applicable).
* Check stepper motor (if applicable).
* Check ignition switch.
* Check TDC sensor.
* Check crank angle sensor.
* Check inhibitor switch (A/T).

* 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.