1991 MITSUBISHI 3000GT display

FUEL SYSTEM - On-vehicle Inspection of MPI Components13-41
POWER SUPPLY AND IGNITION SWITCH-IG
Engine control
unit
16FO29:
Q-i=++=
iA MPI control relay
ml3Yuu
lcmition switch (IG)
@ Harness sideccmnector
62
I
Engine control unit
Engine control unit connector7FUO950
OPERATIONl
While the ignition switch is on, battery power is supplied to the engine control unit, the injector, the airflow sensor, etc.
lWhen the ignition switch is turned on, the battery voltage is applied from the ignition switch to the engine
control unit, which then turns ON the power transistor to energize the control relay coil. This turns ON thecontrol relay switch and the power is supplied from the battery to the engine control unit through the
control relay switch.
INSPECTION
Using Multi-use Tester
IFunctionItem No.Data displayICheck conditionIStandard valueI
Data reading16Engine control unit
power voltageIgnition switch: ONsv
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FUEL SYSTEM - On-vehicle Inspection of MPI Components13-55
INSPECTIONUsing Multi-use Tester

Function
Data readingtern No. Data display
12Sensor airvolume(frequency)
Check conditionEngine stateStandard value
l Engine coolant tem-
700 rpm (Idle)25-50 Hzperature: 80 to 95°C
(176 to 205°F)2,000 rpm70-IOOHzl Lights and accessories:OFFRacingFrequency increasesl Transaxle: Neutralwith racing(P range for vehiclewith AIT)l Steering wheel: Neutral
NOTEWhen the vehicle is new [within initial operation of about 500 km (300 miles)], the air flow sensor output frequency maybe about 10% higher.

Function
Data listItem No. Data displayCheck conditionsEngine conditionsStandard value
34Reset signall Engine warm up700 rpm (Idle)ON
condition2,000 rpmOFF
L;
FunctionItem No. Data display
Data list37Volumetric
efficiencyCheck conditionEngine stateStandard valuel Engine coolant tem-700 rpm (Idle)20-35%
perature: 80 to 95°C
(176 to 205°F)
l Lights, electric cooling2,000 rpm15-30%
fan and accessory opera-tion: OFFl Transaxle: NeutralRacingFrequency increases
(P range for vehiclewith racingwith &T)
l Steering wheel: Neutral
Using Oscilloscope(1) Run the engine at idle speed.
(2) Connect the probe to the oscilloscope pick-up point as
shown in the circuit diagram, and check the waveform.
Regular waveform
03A0203
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13-58FUEL SYSTEM - On-vehicle Inspection of MPI Components
INSPECTION
Using Multi-use Tester
FunctionItem No. Data displayCheck conditionIntake air temperatureStandard valued
Data reading13Sensorignition switch: ON orAt -20°C (-4°F)-20°C
temperatureengine running
At 0°C (32°F)0°C
At 20°C (68°F)20°C
At 40°C (104°F)40°C
At 80°C (176°F)80°C
HARNESS INSPECTION7FUO657
I
connector
7FUO6607FUO661
ITSB I
Check for continuity of the groundcircuit.l Connector: Disconnected
Repair the
harness.,
(@I3 - q ,
Measure the power supply voltage.l Connector: Disconnected
l Ignition switch: ON
Voltage
(V)4.5
- 4.9Repair the
harness.
@@J-@)
SENSOR INSPECTION
(1) Disconnect the air flow sensor connectors.
(2) Measure resistance between terminals @ and
@.
ITemperature [“C (“F)]IResistance (kfl)
I0 (32)I6.0
I20 (681I2.7
wisionI
d

FUEL SYSTEM - On-vehicle Inspection of MPI Components13-61
TROUBLESHOOTING HINTS
Hint 1 : If the barometric pressure sensor is faulty, poor driveability is caused at high altitude, in particular.
L
Hint 2: If the pressure indication of the barometric pressure sensor drops significantly during high speeddriving, check the air cleaner for clogging.
INSPECTIONUsing Multi-use Tester
Function
Data readingItem No.’ Data display
25
Check conditionAltitudeStandard value
Sensor
pressureIgnition switch: ON
At 0 m (0 ft.)760 mmHg
At 600 m (1,969 ft.)
710 mmHg
I/At 1,200 m (3,937 ft.)1660 mmHgI
At 1,800 m (5.906 ft.)610 mmHg
HARNESS INSPECTION
II
L
7FUO657
7FUO66:
Check for continuity of the ground
circuit.l Connector: Disconnected
Repair the
harness.
&@I - q ,
Measure the power supply voltage ofthe barometric pressure sensor.l Connector: Disconnected
l Ignition switch: ON
Voltaqe (V)4.8
- 5.2Repair theharness.
KgpJ-pJ,
Engine contraunit harnessside connects
Check for an open-circuit, or a short-circuit to ground between the enginecontrol unit and the barometric pres-,Y---,A
sure sensor.l
Air flow sensor connector: Dis-(OK) -+ kTOA
connectedlEngine control unit connector:
Disconnected
--I
Repair the
harness.

Jg
7FUO666
1 TSB Revision

id
LFUEL SYSTEM
- On-vehicle Inspection of MPI Components13-63
INSPECTIONUsing Multi-use Tester
LFunctionItem No. Data displayCheck condition
Coolant temperatureStandard valueData reading 21
SensorIgnition switch: ON or
At -20°C (-4°F)-20°C
temperatureengine operatingAt 0°C (32°F)0°C
HARNESS INSPECTION
Check for continuity of the groundcircuit.l Connector: Disconnected
Repair the---+ harness.

7FUO6682
Measure the power supply voltage.l Connector: Disconnected
@ Harness sidel Ignition switch: ON
7FUO669TSB Revision

13-66FUEL SYSTEM - 0n-vehicle Inspection of MPI Components
INSPECTIONUsing Multi-use Tester
FunctionItem No. Data displayCheck conditionThrottle valveStandard value‘d
Data reading14SensorIgnition switch: left ONvoltagefor 15 seconds or moreAt idle position300-1.000 mV
Open slowly
Increases withvalve opening
Open widely4.500-5.500 mV
HARNESS INSPECTIONl Connector: Disconnected
l
lgnrtion switch: ON
l Connector: Disconnected
connector
I
Engine controlCheck for an open-circuit, or a short-
unit harnesscircuit to ground between the engine
side connectorcontrol unit and the throttle positionsensor.
Throttle position sensor connec-
tor: Disconnected
Engine control unit connector:
DisconnectedRepair theB-3 harness.
km-8)
-z =6FU1243
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13-68FUEL SYSTEM - On-vehicle Inspection of MPI Components
IDLE POSITION SWITCHMlBYKAD
Throttle positionse(Idle position switch
2
/bz----;-p
b+i
Throttle shaft turning angle D’20g2
i
Engine control unitI
@ Harness side
connectorIdle position,
@ Equipment side switchconnector
Throttle position
sensor connector
5EL1400
7FUO674
OPERATIONl The idle position switch senses whether the accelerator pedal is depressed or not, converts it into
high/low voltage and inputs the voltage to the engine control unit, which then controls the idle speed
control servo based on the input signal.
lThe voltage in the engine control unit is applied to the idle position switch through a resistor. When the
accelerator pedal is released, the idle position switch is turned on to conduct the voltage to ground. Thiscauses the idle position switch terminal voltage to go low from high.
TROUBLESHOOTING HINTS
If the idle position switch harness and individual part check results are normal but the idle position switchoutput is abnormal, the following troubles are suspected.
’(1) Poorly adjusted accelerator cable or auto-cruise control cable
(2) Poorly adjusted idle position switch (fixed SAS)
INSPECTIONUsing Multi-use Tester
FunctionItem No. Data displayCheck conditionThrottle valveNormal indicationData reading 26
Switch state
Ignition switch: ONON(check by operatingAt idle position
accelerator pedalOpen a littleOFF-J
repeatedly)TSB Revision

FUEL SYSTEM - On-vehicle Inspection of MPI Components13-73
INSPECTION
Using Multi-use Tester
FunctionItem No. Data displayCheck conditionCheck content
Normal stateData reading 22
Crankingl Engine cranking
Compare cranking speedIndicated speed
speedl Tachometer connectedand multi-use tester(check on and off ofto agree
reading
primary current of
ignition coil bytachometer)
NOTE(1)The tachometer indicates a third of the actual engine speed. Therefore, 3 times the tachometer indication is theactual engine speed.(2)When the tachometer is set to the 2-cylinder range, it indicates actual engine speed.
FunctionItem No. Data displayCheck conditionCoolant temperatureStandard value
Data reading22Idle speedl Engine: Running atAt -20°C (-4°F)1,300 - 1,500 rpm
idle
l Idle position switch:ONAt 0°C (32°F)At 20°C (68°F)
At 40°C (104°F)
At 80°C (176°F)1,250
- 1,450 rpm
1
,I 00 - 1,300 rpm
950-1,150rpm
600 - 800 rpm
-m-2,-5v
f-lov
---Normal waveform
Using Oscilloscope
(1) Run the engine at idle speed.
(2) Connect the probe to the oscilloscope pick-up point as
shown in the circuit diagram, and check the waveform.
1 TSB Revision