Mitsubishi 380. Manual — part 628
MULTIPORT FUEL INJECTION (MPI) DIAGNOSIS
MULTIPORT FUEL INJECTION (MPI) <3.8L ENGINE>
13A-604
INSPECTION PROCEDURE 24: Power supply system and ignition switch - IG system.
.
CIRCUIT OPERATION
• Battery positive voltage is applied to the MPI
relay (terminals No. 1, No. 2).
• When the ignition switch is turned to the "ON"
position, the battery positive voltage is applied to
the ECU (terminal No. 43). When the battery pos-
itive voltage is applied, the ECU turns the power
transistor in the ECU "ON" and grounds the MPI
relay coil. With this, the MPI relay turns "ON" and
the battery positive voltage is supplied to the
ECU (terminals No. 51, No. 64) from the MPI
relay (terminal No. 4).
• A battery positive voltage is constantly supplied
to the ECU (terminal No. 42) as the backup
power.
• The ECU (terminals No. 25, No. 29) is grounded
to the vehicle body.
.
TROUBLESHOOTING HINTS (The most
likely causes for this code to be set are:)
• Malfunction of the ignition switch.
• Malfunction of the MPI relay.
• Improper connector contact, open circuit or
short-circuit harness wire.
• Disconnected ECU ground wire.
• Malfunction of the ECU.
• Refer to component locations GROUP-
• Refer to configuration diagrams GROUP-
• Refer to circuit diagrams GROUP-
DIAGNOSIS
STEP 1. Check harness connector B-17X at MPI relay for
damage.
Q: Is the connector in good condition?
YES : Go to Step 2.
NO : Repair or replace it. Refer to GROUP 00E, Harness
Connector Inspection
. Then confirm that the
malfunction symptom is eliminated.
1
2
3
4
AK303017
CONNECTOR: B-17X
FRONT OF VEHICLE
B-17X
AB
HARNESS
CONNECTOR:
COMPONENT SIDE
RELAY BOX
MULTIPORT FUEL INJECTION (MPI) DIAGNOSIS
MULTIPORT FUEL INJECTION (MPI) <3.8L ENGINE>
13A-605
STEP 2. Check the MPI relay.
CAUTION
Because it is not possible to distinguish the top and the
bottom of the MPI relay, inspect it with the triangle mark
printed on the relay facing upward.
(1) Remove the MPI relay.
(2) Check for continuity between the MPI relay terminals No. 2
and No. 3.
• There should be continuity. (approximately 70 ohms)
(3) Use jumper wires to connect MPI relay terminal No. 2 to the
positive battery terminal and terminal No. 3 to the negative
battery terminal.
(4) Check for continuity between the MPI relay terminals No. 1
and No. 4 while connecting and disconnecting the jumper
wire at the negative battery terminal.
• Should be less than 2 ohms. (Negative battery terminal
connected)
• Should be open loop. (Negative battery terminal discon-
nected)
(5) Install the MPI relay.
Q: Is the measured resistance within the specified range?
YES : Go to Step 3.
NO : Replace the MPI relay. Then confirm that the
malfunction symptom is eliminated.
1
2
3
4
AK303017
CONNECTOR: B-17X
FRONT OF VEHICLE
B-17X
AB
HARNESS
CONNECTOR:
COMPONENT SIDE
RELAY BOX
AK204164
1 2
3 4
MFI RERAY
SIDE
CONNECTOR
AB
1 2
3 4
AK203257
MFI RELAY SIDE
CONNECTOR
AB
MULTIPORT FUEL INJECTION (MPI) DIAGNOSIS
MULTIPORT FUEL INJECTION (MPI) <3.8L ENGINE>
13A-606
STEP 3. Measure the power supply voltage at MPI relay
harness side connector B-17X.
CAUTION
Because it is difficult to distinguish the top and bottom of
the MPI relay connector at the wiring harness, inspect it by
using triangle mark on the junction block as reference.
(1) Disconnect the connector B-17X and measure at the
harness side.
(2) Measure the voltage between terminals No. 1, No. 2 and
ground.
• Voltage should be battery positive voltage.
Q: Is battery positive voltage (approximately 12 volts)
present?
YES : Go to Step 4.
NO : Check harness connector A-13 at intermediate
connector for damage, and repair or replace as
required. Refer to, GROUP 00E, Harness Connector
Inspection
. If intermediate connector is in
good condition, repair harness wire between relay
box (9) and MPI relay connector B-17X (terminals No.
1, No. 2) because of open circuit. Then confirm that
the malfunction symptom is eliminated.
1
2
3
4
AK303017
CONNECTOR: B-17X
FRONT OF VEHICLE
B-17X
AB
HARNESS
CONNECTOR:
COMPONENT SIDE
RELAY BOX
2 1
3
4
AK303247
B-17X HARNESS
CONNECTOR:
COMPONENT SIDE
AB
MULTIPORT FUEL INJECTION (MPI) DIAGNOSIS
MULTIPORT FUEL INJECTION (MPI) <3.8L ENGINE>
13A-607
STEP 4. Check harness connector B-20 and B-21 at ECU
for damage.
Q: Is the harness connector in good condition?
YES : Go to Step 5.
NO : Repair or replace it. Refer to GROUP 00E, Harness
Connector Inspection
. Then confirm that the
malfunction symptom is eliminated.
16DB400A
COVER
ENGINE
CONTROL
UNIT
AIR
CLEANER
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