1991 MITSUBISHI 3000GT check engine

13-50FUEL SYSTEM - 0
n-vehicle Inspection of MPI Components
OPERATIONControl Relay Operation
l Drives the fuel pump during cranking and engine operation.
l
When the ignition switch is set to START, current flows from the ignition switch through the control relay
coil to ground. This turns on the control relay switch and drive power is supplied from the battery throughthe control relay switch to the fuel pump.
lWhile the engine is running, the engine control unit keeps the power transistor on and energizes the
control relay coil so that drive power is supplied to the fuel pump.
Fuel Pump Relay No. 2 Operation
lChange the fuel pump discharge in two stages by ON-OFF operation of the relay switch for fuel pumprelay No. 2.
lIf the amount of inlet air is small (the engine load is low), the engine control unit turns on the power
transistor to energize the coil of fuel pump relay No. 2, sending drive power to the fuel pump through the
resistor. If the amount of inlet air is large (the engine load is high), the engine control unit turns off thepower transistor to send drive power directly to the fuel pump without passing through the resistor.
INSPECTIONUsing Multi-use Tester
Function
ActuatortestItem No.
Operation
Check conditionCheck itemNormal condition
07Fuel pump isdriven to cir-l Engine crankingHold return hose withl Forced drive of fuelPulsation is felt
culate fuelfingers to feel pulsationpump
Check is made for aboveindicating fuel flow
two conditionsListen to pump operating
sound near fuel tankOperating sound isheard 2>
I/IIII
cFunctionItem No.Operation
Check conditionNormal condition
Actuatortest
13Turn the fuel pump relayNo. 2 from OFF to ONIgnition switch: ONOperating soundis heard.
HARNESS INSPECTION
k
J------ 7FUO953
lApply battery voltage to thecheckingterminal and operate the
Check the ground circuit of the fuel
pump.
l Connector: Disconnected
@I Harness side
connectorL-J
7FUO554
Repair the
harness.
@pJ-Ground)
J
1 TSB Revision

FUEL SYSTEM- On-vehicle Inspection of MPI Components13-51
Check for continuity between the fuelpump and the checking terminal.-I
l Connector: Disconnected
@N+ 14
Repair the
harness.
(@lig-@g)
@ Harness srdeconnector7FUO95:
Check for continuity between thechecking terminal and the control re-
lay (for fuel pump), and between the
resistor (for fuel pump).
0Control relay (for fuel pump) con-nector: DisconnectedlResistor (for fuel pump) connec-tor: DisconnectedlFuel pump connector: Discon-
nected
Harness side
connector
7FUO960
0
OK
Repair the
harness.
(Cm- Da)!~m-- E@J)8 8
Enaine controlCheck for an open-circuit, or a short-circuitto ground, between the controlrelay (for fuel pump) and the enginecontrol unit.
0Control relay (for fuel pump) con-nector: Disconnected
un? harness
side connector
lEngine control unit connector:
DisconnectedRepair the
harness.
(@J-m@ Harness side
connector
Check for continuity between thecontrol relay (for fuel pump) and the
resistor (for fuel pump).
0Control relay (for fuel pump) con-nectar: Disconnectedl Resistor (for fuel pump) connec-tor: DisconnectedRepair the
harness.
(@pJ-@iJ)
7FUO962
Measure the power supply voltage ofthe control relay.
@I Harness side
connector
rl Connector: DisconnectedlIgnition switch: START (when
checking
@@IlIgnition switch: ON (when check-
ing
@@IVoltage
(VI8 or higher
1 ‘7FUO47fITSB Revision

13-52FUEL SYSTEM - 0
n-vehicle Inspection of MPI Components
-i8
@ Harness side
connector
Check for an open-circuit, or a short-circuit to ground, between the controlrelay and the engine control unit.l
Control relay connector: Discon-
nectedl
Engine control unit connector:
Disconnected
Engine controlunit harness
side connector
7FUO475g
/Check for continuity between thecontrol relay and the control relay (for
fuel pump).l
Control relay connector: Discon-
nectedl
Control relay (for fuel pump) con-nector: Disconnected
zonnector8 Harness side
connector
/
7FUO96:
T
Check for continuity of the ground
circuit.l Connector: Disconnected
!
Repair the
harness.
@pJ-Ground)
7FUO476
Check for an open-circuit, or a short-circuit to ground, between the controlrelay (for fuel pump) and the fuel
pump.l
Control relay (for fuel pump)connector: DisconnectedlFuel pump connector: Discon-nectedRepair the
harness.
(@@-@lTJ)
@I Harness sidtconnector@Harness side
connector
I7FUO964
CONTROL RELAY INSPECTIONRefer to
P.13-43.TSB Revision
1

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
TSB Revision

13-56FUEL SYSTEM - 0
n-vehicle Inspection of MPI Components
HARNESS INSPECTION
--barness side
connector
*7FUO656
connector
7FUO6574
?
@ Harness sideEngine c&lconnector
unit harness
side connector
I -
1
m
!h 4.7Fuo745u
Measure the power supply voltage.l Connector: Disconnected
l Ignition switch: ON
Voltage
(V)
eoair the
check the
control relay.
Measure the terminal voltage.l Connector: Disconnected
l Ignition switch: ON
Check for continuity of the ground
circuit.l Connector: Disconnected
Repair the
harness.
@El - I@)
Check for continuity between the air
flow sensor and the engine control
unit.l Air flow sensor connector: Dis-f
connected10l Engine control unit connector:
‘L-/Disconnected. .Rr.annir th(
t
I ‘“yu’3harness.
TSB Revision

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