ECU MITSUBISHI TRITON 1997 Owner's Manual

MPI ± Troubleshooting13A-27
INSPECTION PROCEDURE 6
Initial combustion but no complete combustion
(starting impossible)
Probable cause
In such cases as the above, the cause is probably that the spark plugs are generating
sparks but the sparks are weak, or the initial mixture for starting is not appropriate.
Malfunction of the ignition system

Malfunction of the injector system

Foreign materials in fuel

Poor compression

Malfunction of the engine-ECU
Check battery voltage when cranking.
OK:8 V or higherNGCheck the battery. (Refer to GROUP 54 ± Battery.)
OK
MUT-II: Check if uncompleted combustion occurs.
(Refer to P.13A-48, INSPECTION PROCEDURE 36.)
OK
Can any sound be heard from the injectors when cranking?NGCheck the injector system, (Refer to P.13A-19, INSPECTION PRO-
CEDURE FOR DIAGNOSIS CODE 41.)
OK
Is starting good if the engine is cranked with the accelerator pedal
slightly depressed?Ye sCheck ISC servo for op-
eration sound.
(Refer to P.13A-90.)NGCheck the ISC servo sys-
tem. (Refer to P.13A-45,
INSPECTION PROCE-
DURE 31.)
OK

Clean the throttle valve area. (Refer to P.13A-78.)

Check and adjust the fixed SAS. (Refer to P.13A-79.)
No
Check the ignition timing when cranking.
OK:Approx. 5BTDCNGCheck that the distributor is installed properly.
OK
Check the following items.

Check the ignition coil, spark plugs, spark plug cables. (Refer to GROUP 16 ± On-vehicle Service.)

Check if the injectors are clogged.

Check the compression pressure. (Refer to GROUP 11 ± On-vehicle Service.)

Check fuel lines for clogging.

Check if foreign materials (water, alcohol, etc.) got into fuel.

MPI ± Troubleshooting13A-33
INSPECTION PROCEDURE 12
When the engine is hot, it stalls at idling. (Die out)
Probable cause
In such cases as the above, the cause is probably that ignition system, air/fuel mixture,
idle speed control (ISC) or compression pressure is defective.
In addition, if the engine suddenly stalls, the cause may also be a defective connector
contact.
Malfunction of the ignition system

Malfunction of air-fuel ratio control system

Malfunction of the ISC system

Drawing air into intake system

Improper connector contact
Were the battery terminals disconnected?Ye sAfter warming-up, let the engine run at idling for 10 minutes.
No
MUT-II Self-Diag code
Are diagnosis codes displayed?Ye sRefer to P.13A-10, INSPECTION CHART FOR DIAGNOSIS
CODES.
No
Check the ISC servo for operation sound. (Refer to P.13A-90.)NGCheck the ISC servo system.
(Refer to P.13A-45, INSPECTION PROCEDURE 31.)
OK
Check the injector for operation sound.NGCheck the injector system. (Refer to P.13A-19, INSPECTION PRO-
CEDURE FOR DIAGNOSIS CODE 41.)
OK
Does the engine stall right after the accelerator pedal is released?Ye sClean the throttle valve
area. (Refer to P.13A-78.)Check and adjust the
fixed SAS.
(Refer to P.13A-79.)
No
Does the engine stall easily again?NoWhile carrying out an intermittent malfunction simulation test (Refer
to GROUP 00 ± Points to Note for Intermittent Malfunctions.), check
for sudden changes in the signals shown below.

Crank angle sensor signal

Air flow sensor signal

Injector drive signal
Primary and secondary
ignition signal

Fuel pump drive signal

Engine-ECU power supply
voltage
Ye s
MUT-II: Engine stalling inspection when the engine is warm and
idling. (Refer to P.13A-50, INSPECTION PROCEDURE 39.)
OK
Check the ignition timing.
(Refer to GROUP 11 ± On-vehicle Service.)NGCheck that the distributor is installed properly.
OK
Check the following items.

Check the ignition coil, spark plugs, spark plug cables. (Refer to GROUP 16 ± On-vehicle Service.)

Check if the injectors are clogged.

Check the compression pressure. (Refer to GROUP 11 ± On-vehicle Service.)

Check if foreign materials (water, alcohol, etc.) got into fuel.

MPI ± Troubleshooting13A-39
INSPECTION PROCEDURE 23
Power supply system and ignition switch-IG system
Probable cause
When an ignition switch ON signal is input to the engine-ECU, the engine-ECU turns
the control relay ON. This causes battery voltage to be supplied to the engine-ECU,
injectors and air flow sensor.
Malfunction of the ignition switch

Malfunction of the control relay

Improper connector contact, open circuit or
short-circuited harness wire

Disconnected engine-ECU earth wire

Malfunction of the engine-ECU
Check the control relay. (Refer to P.13A-86.)NG
Replace
OK
Measure at the control relay connector C-53.

Disconnect the connector, and measure at the harness side.

Voltage between 3, 4 and earth
OK:System voltageNGCheck the harness wire between battery and control relay connector,
and repair if necessary.
OK
Check the engine-ECU power supply and earth circuit.
(Refer to P.13A-53, INSPECTION PROCEDURE 42.)

MPI ± Troubleshooting13A-40
INSPECTION PROCEDURE 24
Fuel pump system
Probable cause
The engine-ECU turns the control relay ON when the engine is cranking or running,
and this supplies power to drive the fuel pump.
Malfunction of the fuel pump relay

Malfunction of the fuel pump

Improper connector contact, open circuit or
short-circuited harness wire

Malfunction of the engine-ECU
Check the fuel pump operation. (Refer to P.13A-84.)NGCheck the fuel pump circuit.
(Refer to P.13A-53, INSPECTION PROCEDURE 43.)
OK
Check the fuel pump relay. (Refer to P.13A-86.)NG
Replace
OK
Measure at the fuel pump relay connector C-54.

Connect the connector.

Voltage between 1 and earth

MUT-II Actuator test: Fuel pump drive
OK:System voltageNGCheck the fuel pump drive control circuit.
(Refer to P.13A-54, INSPECTION PROCEDURE 44.)
OK
Check the harness wire between fuel pump relay connector and
fuel pump drive terminal, and repair if necessary.
INSPECTION PROCEDURE 25
Idle position switch system
Probable cause
The idle position switch inputs the condition of the accelerator pedal, i.e. whether
it is depressed or released (HIGH/LOW), to the engine-ECU.
The engine-ECU controls the idle speed control servo based on this input.
Maladjustment of the accelerator pedal

Maladjustment of the fixed SAS

Maladjustment of the idle position switch and throttle
position sensor

Improper connector contact, open circuit or
short-circuited harness wire

Malfunction of the engine-ECU
Check the idle position switch. (Refer to P.13A-87.)NGReplace
OK
Measure at the throttle position sensor connector A-47.

Disconnect the connector, and measure at the harness side.

Voltage between 2 and earth (Ignition switch: ON)
OK:4 V or higher

Continuity between 1 and earth
OK:ContinuityNGCheck the following
connector. C-51NG
Repair
OK
Check trouble symptom.
NG
Check the harness wire between engine-ECU and throttle position
sensor connector.
OK
Replace the engine-ECU.
NG
Repair
OK
Check the following
connector. A-47NG
Repair
OK
Check trouble symptom.
NG
Replace the engine-ECU.

MPI ± Troubleshooting13A-41
INSPECTION PROCEDURE 26
Ignition switch-ST system <M/T>
Probable cause
The ignition switch-ST inputs a HIGH signal to the engine-ECU while the engine is
cranking.
The engine-ECU controls fuel injection, etc. during starting based on this input.
Malfunction of ignition switch

Improper connector contact, open circuit or
short-circuited harness wire

Malfunction of the engine-ECU
Check the harness wire between the engine-ECU connector (termi-
nal No.71) and earth, and repair if necessary.
Measure at the engine-ECU connector C-51.

Disconnect the connector, and measure at the harness side.
1. Voltage between 51 and earth (Ignition switch: START)
OK:8V or more
2. Continuity between 71 and earth
OK:Continuity1. NGCheck the following
connector. C-51NG
Repair
OK
Check trouble symptom.
NG
Check harness wire be-
tween the engine-ECU
and ignition switch con-
nector.NG
Repair
OK
Check the ignition switch.
(Refer to GROUP 54 ± Ignition Switch and Immobilizer system.)
OK
Check the following
connector. C-51NG
Repair
OK
Check trouble symptom.
NG
Replace the engine-ECU.
2. NG

MPI ± Troubleshooting13A-42
INSPECTION PROCEDURE 27
Ignition switch-ST and inhibitor switch system <A/T>
Probable cause

The ignition switch-ST inputs a HIGH signal to the engine-ECU while the engine
is cranking.
The engine-ECU controls fuel injection, etc. during starting based on this input.

The inhibitor switch inputs the condition of the select lever, i.e. whether it is in
P or N range or in some other range, to the engine-ECU.
The engine-ECU controls the idle speed control (ISC) servo based on this input.
Malfunction of ignition switch

Malfunction of inhibitor switch

Improper connector contact, open circuit or
short-circuited harness wire

Malfunction of the engine-ECU.
Check the following
connector. B-01
OK
Measure at the inhibitor switch connector B-01.

Disconnect the connector, and measure at the harness side.
1. Voltage between 6 and earth (Ignition switch: ON)
OK:System voltage
2. Continuity between 5 and earth
OK:Continuity
3. Voltage between 6 and earth

Ignition switch: START

Disconnect engine-ECU connector.
OK:System voltage1. NGCheck the following
connectors.
C-01, C-51, C-57NG
Repair
OK
Check trouble symptom. 2. NG
3. NG
Check the following
connector.
C-01, C-57, C-70NG
Repair
OK
Check trouble symptom.
NG
NG
Repair
Check harness wire be-
tween inhibitor switch and
ignition switch connector.
OK
Check the ignition switch.
(Refer to GROUP 54 ± Ignition Switch and Immobilizer system.)
OK
NG
Repair
OK
Check trouble symptom.
NG
Check harness wire be-
tween engine-ECU and
inhibitor switch connector.NG
Repair
OK
Replace the engine-ECU.
NG
ReplaceCheck the inhibitor switch.
(Refer to GROUP 23 ± On-vehicle Service.)
NG
Check the harness wire
between the engine-ECU
connector and inhibitor
switch connector.NG
Repair
OK
Replace the engine-ECU.
OK
Check trouble symptom.
NG
Check the harness wire between the inhibitor switch connector
and earth, and repair if necessary.
Check the following
connectors.
A-52X, C-19, C-57NG
Repair

MPI ± Troubleshooting13A-43
INSPECTION PROCEDURE 28
Power steering fluid pressure switch system
Probable cause
The presence or absence of power steering load is input to the engine-ECU.
The engine-ECU controls the idle speed control (ISC) servo based on this input.
Malfunction of power steering fluid pressure switch

Improper connector contact, open circuit or
short-circuited harness wire

Malfunction of the engine-ECU
Check the power steering fluid pressure switch.
(Refer to GROUP 37A ± On-vehicle Service.)NG
Replace
OK
Measure at the power steering fluid pressure switch connector
A-74.

Disconnect the connector, and measure at the harness side.

Voltage between 1 and earth (Ignition switch: ON)
OK:System voltageNGCheck the following
connector. C-50NG
Repair
OK
Check trouble symptom.
NG
Check harness wire be-
tween engine-ECU and
power steering fluid pres-
sure switch connector.NG
Repair
OK
Replace the engine-ECU.
OK
Check the following
connector. A-74NG
Repair
OK
Check trouble symptom.
NG
Replace the engine-ECU.
INSPECTION PROCEDURE 29
A/C switch and A/C relay system
Probable cause
When an A/C ON signal is input to the engine-ECU, the engine-ECU carries out
control of the idle speed control (ISC) servo, and also operates the A/C compressor
magnetic clutch.
Malfunction of A/C control system

Malfunction of A/C switch

Improper connector contact, open circuit or
short-circuited harness wire

Malfunction of the engine-ECU
Check the A/C compressor relay.
(Refer to GROUP 55 ± On-vehicle Service.)NG
Replace
OK
Measure at the engine-ECU connectors C-49, C-50.

Disconnect the connector, and measure at the harness side.
<Vehicles without immobilizer system>

Voltage between 22 and earth, and 45 and earth
(Ignition switch: ON, A/C switch: ON)
OK:System voltage

Short circuit between 22 and earth
(Ignition switch: ON, A/C switch: ON)
OK:A/C compressor clutch turns on.
<Vehicles with immobilizer system>

Voltage between 8 and earth, and 45 and earth
(Ignition switch: ON, A/C switch: ON)
OK:System voltage

Short circuit between 8 and earth
(Ignition switch: ON, A/C switch: ON)
OK:A/C compressor clutch turns on.NGCheck the A/C system. (Refer to GROUP 55 ± On-vehicle Service.)
OKCheck the following
connectors. C-49, C-50NG
Replace
OK
Check trouble symptom.
NG
Replace the engine-ECU.

MPI ± Troubleshooting13A-44
INSPECTION PROCEDURE 30
Ignition circuit system
Probable cause
The engine-ECU interrupts the ignition coil primary current by turning the power transistor
inside the engine-ECU ON and OFF.
Malfunction of ignition switch.

Malfunction of power transistor unit

Improper connector contact, open circuit or
short-circuited harness wire

Malfunction of the engine-ECU
NGCheck the following
connector. C-88NG
Repair
OK
Check trouble symptom.
NG
Check the harness wire
between ignition coil and
ignition switch connector.NG
Repair
OK
Check the ignition switch.
(Refer to GROUP 54 ± Ignition Switch and Immobilizer System.)
OK
Check the following
connectors. A-65, A-70NG
Repair
OK
Check trouble symptom.NGCheck ignition coil and power transistor unit system. (Refer to
P.13A-56, INSPECTION PROCEDURE 48.)
OK
Measure at the power transistor unit connector A-70.

Disconnect the connector and measure at the harness side.

Continuity between 2 and earth
OK: ContinuityNG
Check the harness wire between power transistor unit connector
and earth, and repair if necessary.
Measure at the ignition coil connector A-65.

Disconnect the connector and measure at the harness side.

Voltage between 2 and earth (Ignition switch: ON)
OK: System voltage

MPI ± Troubleshooting13A-45
INSPECTION PROCEDURE 31
Idle speed control (ISC) servo (Stepper motor) system
Probable cause
The engine-ECU controls the intake air volume during idling by opening and closing
the servo valve located in the bypass air passage.
Malfunction of ISC servo

Improper connector contact, open circuit or
short-circuited harness wire

Malfunction of the engine-ECU
Check the ISC servo
(Refer to P.13A-90.)NG
Replace
OK
Measure at the ISC servo connector A-50.

Disconnect the connector and measure at the harness side.

Voltage between 2 and earth, and 5 and earth (Ignition switch:
ON)
OK:System voltageNGCheck the harness wire between control relay and ISC servo con-
nector, and repair if necessary.
OK
Measure at the engine-ECU connector C-49.

Disconnect the connector, measure at the harness side.

Voltage between each of 4, 5, 17, 18 and earth (Ignition switch:
ON)
OK:System voltageNGCheck the following
connector. A-50NG
Repair
OK
Check trouble symptom.
NG
Check harness wire between engine-ECU and ISC servo connector,
and repair if necessary.
OK
Check the following
connector. C-49NG
Repair
OK
Check trouble symptom.NGReplace the engine-ECU.
INSPECTION PROCEDURE 32
Purge control solenoid valve system
Probable cause
The purge control solenoid valve controls the purging of air from the canister located
inside the intake manifold.
Malfunction of solenoid valve

Improper connector contact, open circuit or
short-circuited harness wire.

Malfunction of the engine-ECU
Check the purge control solenoid valve.
(Refer to GROUP 17 ± Emission Control System.)NG
Replace
OK
Measure at the purge control solenoid valve connector A-48.

Disconnect the connector and measure at the harness side.

Voltage between 2 and earth (Ignition switch: ON)
OK:System voltageNGCheck the harness wire between control relay and solenoid valve
connector, and repair if necessary.
OK
Measure at the engine-ECU connector B-49.

Disconnect the connector and measure at the harness side.

Voltage between 9 and earth (Ignition switch: ON)
OK:System voltageNGCheck the following
connector. A-48NG
Repair
OK
Check trouble symptom.
NG
Check the harness wire between engine-ECU and solenoid valve
connector, and repair if necessary.
OK
Check the following
connector. B-49NG
Repair
OK
Check trouble symptom.
NG
Replace the engine-ECU.

MPI ± Troubleshooting13A-46
INSPECTION PROCEDURE 33
EGR control solenoid valve system
Probable cause
The EGR control solenoid valve is controlled by the negative pressure resulting from
EGR operation leaking to port ªAº of the throttle body.
Malfunction of solenoid valve

Improper connector contact, open circuit or
short-circuited harness wire.

Malfunction of the engine-ECU
Check the EGR control solenoid valve.
(Refer to GROUP 17 ± Emission Control System.)NG
Replace
OK
Measure at the EGR control solenoid valve connector A-49.

Disconnect the connector and measure at the harness side.

Voltage between 1 and earth (Ignition switch: ON)
OK:System voltageNGCheck the harness wire between control relay and solenoid valve
connector, and repair if necessary.
OK
Measure at the engine-ECU connector C-49.

Disconnect the connector and measure at the harness side.

Voltage between 6 and earth (Ignition switch: ON)
OK:System voltageNGCheck the following
connector. A-49NG
Repair
OK
Check trouble symptom.
NG
Check the harness wire between engine-ECU and solenoid valve
connector, and repair if necessary.
OK
OK
Check trouble symptom.
NG
Replace the engine-ECU.
Check the following
connector. C-49NG
Repair