1991 MITSUBISHI 3000GT Service Manual

iFUEL SYSTEM
- On-vehicle Inspection of MPI Components
INSPECTION
Using Oscilloscope13-71
::Normal waveform(1) Run the engine at an idle speed.
(2) Connect the probe to the oscilloscope pick-up point as
shown in the circuit diagram, and check the waveform.
7Fuo495HARNESS INSPECTION
= 7FUO496r
i2
@ Harness sideconnectorF
7FUO497
J
Measure the power supply voltagel Connector: Disconnected
l Ignition switch: ON
Voltage
(VI, OK(I:
sv
ib
02
Repair the
harness.
(@m - Con-
trol relay)
ICheck for continuity of the groundcircuit.l Connector: Disconnected
3
~,
Check the voltage of the output err-cuit.l Connector: Disconnected
l Ignition switch: ON
Voltaae
(V)4.8
- 5.2Repair the
harness.
(@El-ED
I7FUO498
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13-72FUEL SYSTEM - On-vehicle Inspection of MPI Components
CRANK ANGLE SENSOR
co.ntiector
Output characteristic
LTime
7FUO682
MllYiAC
Control relay-I-
Crank angle sensorsideA3
Crank angle sensor/\
‘=
Engine controlunft69I
1
h5v
7FUO499
OPERATIONl
The crank angle sensor senses the crank angle (piston position) of each cylinder, converts it into a pulse
signal and inputs it to the engine control unit, which then computes the engine speed and controls the fuelinjection timing and ignition timing based on the input signal.
lPower to the crank angle sensor is supplied from the control relay and is grounded to the body. The crank
angle sensor generates a pulse signal as it repeatedly connects and disconnects between 5 V voltagesupplied from the engine control unit and ground.
TROUBLESHOOTING HINTSHint 1: If unexpected shocks are felt during driving or the engine stalls suddenly during idling, shake the
crank angle sensor harness. If this causes the engine to stall, poor contact of the sensor connector is
suspected.Hint 2: If the crank angle sensor outputs a pulse signal when the ignition switch is turned ON (with the
engine not running), a faulty crank angle sensor or engine control unit is suspected.
Hint 3:
If the tachometer reads 0 rpm when the engine that has failed to start is cranked, faulty crank angleHint 4:sensor or broken timing belt is suspected.
If the tachometer reads 0 rpm when the engine that has failed to start is cranked, the primary current
of the ignition coil is not turned on and off. Therefore, troubles in the ignition circuit and ignition coil orfaulty power transistor is suspected.
Hint 5: If the engine can be run at idle even though the crank angle sensor reading is out of specification,troubles are often in other than the crank angle sensor.
[Examples](1) Faulty engine coolant temperature sensor
(2) Faulty idle speed control servo
(3) Poorly adjusted reference idle speed
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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.
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13-74FUEL SYSTEM - 0n-vehicle Inspection of MPI Components
HARNESS INSPECTION
J1@ Harness side
connector
1
7FUO496
Measure the power supply voltage.
IsvRepair the
harness.
(@I@ - Con-
trol relay)
r2
t-@ Harness side
connector
Check for continuity of the groundcbrcux.l Connector: Disconnected
7FUO497
3
‘L‘7FUO498
El3
Repair the
harness.
!?.!!ni )
Check the voltage of the output cir-cuit.l Connector: Disconnected
l lgnrtion switch: ON
Voltage
(VI4.8
- 5.2
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FUEL SYSTEM - On-vehicle Inspection of MPI Components
L
L
IGNITION SWITCH-ST
lgnitlon switch (ST)
I
Enaine control unit connector
7FUO653
Engine control unit
1 FU0638
OPERATION
lThe ignition switch-ST inputs a high signal to the engine control unit while the engine is cranking. Theengine control unit provides fuel injection control, etc., at engine startup based on this signal.
lWhen the ignition switch is set to START, the battery voltage at cranking is applied through the ignitionswitch to the engine control unit, which detects that the engine is cranking.
INSPECTION
Using Multi-use Tester
FunctionItem No. Data displayCheck conditionEngineNormal indication
Data reading18Switch stateIgnition switch: ONstopOFF
CrankingON
HARNESS INSPECTION
1
L6FU1258
2
1
Engine control
side connector
IY-6FU1259
Measure the input voltage to theengine control unit.nlEngine control unit connector:Disconnectedl Ignition switch: START
Check for continuity of the groundcircuit.
lEngine control unit connector:Disconnected
Repair the
harness.
(m - Ground)
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13-76FUEL SYSTEM - On-vehicle Inspection of MPI Components
IGNITION SWITCH-ST AND INHIBITOR SWITCH
lqnition switch (ST)
@ Equipment side
connectorStarter S Control
terminalrelay
f,BL
Engine control unit connector7FUO625
Engine control unit
@ Harness side
connector
7FUO653
OPERATIONl
The ignition switch-ST inputs a high signal to the engine control unit while the engine is cranking. Theengine control unit provides fuel injection control, etc., at engine startup based on this signal.
l
When the ignition switch is set to START, the battery voltage at cranking is applied through the ignitionswitch and inhibitor switch to the engine control unit, which detects that the engine is cranking.
In case the selector lever is in a position other than the P/N range, the battery voltage is not applied to theengine control unit.
l
The inhibitor switch converts the selector lever position (whether it is at the P/N range or at others) into
high/low voltage and inputs it to the engine control unit, which then controls the idle speed control servobased on this signal.
l
The battery voltage in the engine control unit is applied through a resistor to the inhibitor switch. When the
selector lever is set to the P/N range, continuity is produced between the inhibitor switch terminal of the
engine control unit and ground through the starter motor, thereby making the terminal voltage go low.
TROUBLESHOOTING HINTS
If the inhibitor switch harness and individual part check have resulted normal but the inhibitor switch output isabnormal, poorly adjusted control cable is suspected.
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FUEL SYSTEM - On-vehicle Inspection of MPI Components13-77INSPECTION
Using Multi-use Tester
LIGNITION SWITCH-ST
FunctionItem No. Data displayCheck conditionEngineNormal rndrcation
Data reading18Switch stateIgnition switch: ON
stopOFF
CrankingONINHIBITOR SWITCH
FunctionItem No. Data displayCheck conditionSelect lever positionNormal indicationData reading 29
Shift
Ignition switch: ONP or NP or Nposition
D.2,L or RD.2.L or RHARNESS INSPECTION
@ Harness sideconnector
OlA0206
2
@ Harness srdeconnectorl
Engine control unit connector:
Connectedl
InhibItor switch connector: Dis-6a
L-J
cl3
connectedl Ignition switch: ON
Repair the
harness.Voltage
(VI@El - El)
OlA0206LII
Engine control
unit harness
side connector
Measure the power supply voltage of
the inhibitor switch.
-lEngine control unit connector:
Disconnectedl
lnhibrtor switch connector: Dis-
connectedl Ignition switch: START
Voltage
(V)
rLlltXK IlIt:Lpower supplycircuit.
Measure the inhibitor switch terminalinput voltage.
Measure the input voltage of enginecontrol unit.lEngine control unrt connector:DisconnectedlFer;it;r switch connector: Con-
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13-78FUEL SYSTEM - 0n-vehicleInspection of MPI Components
VEHICLE SPEED SENSORMIBYPM
Vehrcle speed sensor
(reed switch\)Speedometer
Terminal voltage
(V)
@ Equipment side
Vehicle speed [km/h (mph)]
162461
Engine control unit
7FUO925
Engine control unit connector7FUO653
OPERATION
lThe vehicle speed sensor which is located in the speedometer converts the vehicle speed into a pulse
signal and inputs it to the engine control unit, which then provides the idle speed control, etc. based on
this signal.
lThe vehicle speed sensor generates the vehicle speed signal by repeatedly opening and closing betweenthe voltage of about 5 V applied from the engine control unit and ground using a reed switch.
TROUBLESHOOTING HINTS
If there is an open or short circuit in the vehicle speed sensor signal circuit, the engine may stall when thevehicle is decelerated to stop.
HARNESS INSPECTION
unit harness
side connectorCheck the vehicle speed sensor out-
put circuit for continuity.
lEngine control unit connector:
Disconnected
lMove the vehicle.
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d