1991 MITSUBISHI 3000GT Service Manual

FUEL SYSTEM - On-vehicle .lnspection of MPI Components13-111
INSPECTIONUsing Multi-use Tester
FunctionItem No. Data display
Data reading 45
Stepper
1
motor steps
~
Check condition
l Engine coolant tem-
perature: 80 to 95°C
(176 to 205°F)
0 Lamps, electric cooling
fan, accessory units:
All OFFl Transaxle: Neutral(P range for vehiclewith AA>l Steering wheel: Neutrall Idle position switch: ON(compressor clutch
to be ON if air condi-
tioner switch is ON)l Engine: idling
Load stateStandard value
;;rnditioner switch:2 - 12 stp&conditioner switch:
25 - 65 stp
l $irNconditioner switch:15 - 63 stp0 Selector lever:Shift to D range
NOTEWhen the vehicle is new [within initial operation of about 500 km (300 miles)], the stepper motor steps may be about 30steps more than standard.
CautionWhen the selector lever is shifted to the “D”range, the brakes must be used to prevent the vehicle frommovingforward.
03A020
Using Oscilloscope(1) Connect the probe to each oscilloscope pick-up point as
shown in the circuit diagram.
(2) Start the engine.
(3) When the air conditioner switch is turned on, the idling
speed increases to operate the idle speed control. Check
the instantaneous waveform.
NOTEKeep in mind that the waveform can be observed only
when idle speed control is in operation.
1 TSB Revision

13-112FUEL SYSTEM - 0
n-vehicleInspection of MPI Components
HARNESS INSPECTION
Measure the power supply voltage ofidle speed control servo.l
Idle speed control servo connec-tor: Disconnectedl Ignition switch: ON
Connector
connector
OlLO395- WI)
Engine control
Check for an open-circuit, or a short-circuit to ground between the enginecontrol unit and the idle speed control
servo.l
Engine control unit connector:
Disconnectedl
Idle speed control servo connec-tar: Disconnected
ACTUATOR I’NSPECTIONChecking the Operation Sound
(1)Check that the operation sound of the stepper motor can be
heard after the ignition is switched ON (but without starting
the motor).
(2) If the operation sound cannot be heard, check the stepper
motor’s activation circuit.
If the circuit is normal, it is probable that there is a
malfunction of the stepper motor or of the engine control
unit.
TSB Revision

idFUEL SYSTEM
- On-vehicle Inspection of MPI Components13-113
‘El
‘a
~
63
7FUOOlO(stepper motor)
7FUO98CIdle speed
MD998463
7FUOO78
Checking the Coil Resistance(1) Disconnect the idle speed control servo connector and
connect the special tool (test harness).
(2) Measure the resistance between terminal @ (white clip of
the special tool) and either terminal @ (red clip) or terminal@ (blue clip) of the connector at the idle speed control
servo side.
Standard value: 28
- 33 !2 at 20°C (68°F)
(3) Measure the resistance between terminal @ (green clip of
the special tool) and either terminal @ (yellow clip) or
terminal @ (black clip) of the connector at the idle speed
control servo side.
Standard value: 28
- 33 CR at 20°C (68°F)
Operational Check(1) Remove the throttle body.
(2) Remove the stepper motor.
(3) Connect the special tool (test harness) to the idle speed
control servo connector.
(4) Connect the positive
0 terminal of a power supply (approx
6 V) to the white clip and the green clip.
TSB Revision

13-114FUEL SYSTEM - On-vehicle Inspection of MPI Components
(5) With the idle speed control servo as shown in the
illustration, connect the negative
0 terminal of the power
supply to each clip as described in the following steps, and
check whether or not a vibrating feeling (a feeling of very
(slight vibration of the stepper motor) is generated as aJresult of the activation of the stepper motor.@Connect the negative
0 terminal of the power supply to
the red and black clip.@Connect the negative
0 terminal of the power supply to
the blue and black clip.@Connect the negative
0 terminal of the power supply to@the blue and yellow clip.
Connect the negative
0 terminal of the power supply to
the red and yellow clip.@Connect the negative
0 terminal of the power supply to
the red and black clip.@ Repeat the tests in sequence from @ to
0.(6) If, as a result of these tests, vibration is detected, the
stepper motor can be considered to be normal.
TSB Revision

FUEL SYSTEM - On-vehicle Inspection of MPI Components
IGNITION COIL AND POWER TRANSISTOR
MlBYVABEquipment side
connector@ Harness side
connector@ Harness side connector
Tachometer
-1Battery
/gnition coil1 3
Engine control unit
\/\/\IAL“8 “6.,,523No. 2No. 3
No 5No. 6
* transistor
5Y
lgnltlontamingadjust-
mentconnectof
11104
d
w5V
7FU1059Engine control unitconnector
7FUO453
OPERATION
lWhen the power transistor unit A is turned on by the signal from the engine control unit, primary current
flows to the ignition coil A. When the power transistor unit A is turned off, the primaty current is shut off
and a high voltage is induced in the secondary coil A, causing the ignition plugs of No. 1 and No. 4
cylinders to spark. When the
power transistor unit B is turned off, the ignition plugs of No. 2 and No. 3
cylinders spark.
L
lWhen the engine control unit turns off the transistor in the unit, the battery voltage in the unit is applied to
the power transistor unit to turn it on. When the engine control unit turns on the transistor in the unit, the
power transistor unit is turned off.
TSB Revision

13-116FUEL SYSTEM - 0
n-vehicle Inspection of MPI Components
INSPECTION
Using Multi-use Tester
(d
FunctionItem No. Data displayCheck condition
Engine state
Standard valueData reading 44
Ignitionadvancel Engine: Warming up
750 rpm (Idle)7 - 23”BTDCl Timing light: Set (settiming light to check2,000 rpm30 - 40”BTDC actual ignition timing)28 - 35”BTDC

‘
Function
Data listItem No.Data displayCheckTerminalStandard value
condition
condition
36Continuity present or
not present betweenl Engine:
IdlingIgnition timing ad-ON
ignition timing adjustmentjustment terminal isterminal and groundgrounded
Ignition timing ad-OFFjustment terminal is
disconnected from
ground
Function
Actuator testItem No.
DriveCheck conditionNormal condition
17Set to ignition timingl Engine: idling5”BTDCadjustment model Timing light: set\
($Gizi)
IJ
\LIOV _
ovep~,. ..~_~.~ fA t---.-
I
Normal waveform03AO207
(
j /’ II
IOV _I ’/
/ 1ovIJ
Normal waveform
Using Oscilloscope1. Primary signal of ignition coil
(I) Run the engine at an idle revolution speed.
(2) Connect the probe to oscilloscope pick-up point 1 as
shown in the circuit diagram, and check the primary
signal of the ignition coil.
2. Control signal of power transistor
Connect the probe to oscilloscope pick-up point
2 as shown
in the circuit diagram, and check the control signal of the
power transistor.
TSB Revision

FUEL SYSTEM - On-vehicle Inspection of MPI Components13-117
HARNESS INSPECTION
connectorl Connector: Disconnected
l Ignition switch: ON
Check for an open-circuit, or a short-
P
circuit to ground between the engine
control unit and the power transistor.l
Engine control unit connector:
Disconnectedl
Power transistor connector: Dis-connectedEngineRepair thecontrolunit-+ harness.harness(@@J-1101/)stdeconnector
T6FU1251
Check for an open-circuit, or a short-circuit to ground between the power
transistor and the ignition coil.l
Ignition coil connector: Discon-netted
l
Power transistor connector: Dis-
connected
Repair the
7FUO699
TSB Revision

13-118FUEL SYSTEM- On-vehicle Inspection of MPI Components
connector
7FUO700
7FUO701
Check for continuity of the ground
circuit.
(1Il Connector: Disconnected
Repair the
harness.@pJ
-Ground)
Measure the voltage of the controlslgnal circuit of the power transistor.l Connector: Disconnected
l
lgnrtion switch: START
Voltage
(VI0.5
- 4.0
f
q7
Repair the
harness.
Measure the voltage of the ignition
timinq adiustment terminal.
- _l Ignition switch: ON
Voltage
(V)4.0
- 5.2
ACTUATOR INSPECTIONRefer to GROUP 16
- Ignition System.
TSB Revision