Mitsubishi Space Star. Manual — part 72
MPI –
Troubleshooting
13B-75
Wave Pattern Observation Points
Check that the standard wave pattern appears when the ISC servo is operating.
Point A: Presence or absence of induced electromotive force from the motor turning. (Refer to the abnormal
wave pattern.)
Contrast with standard wave pattern
Probable cause
Induced electromotive force does not appear or is extremely small.
Motor is malfunctioning
Point B: Height of coil electromotive force
Contrast with standard wave pattern
Probable cause
Coil reverse electromotive force does not appear or is extremely small.
Short in the coil
Examples of Abnormal Wave Pattern
Example 1
Cause of problem
Motor is malfunctioning. (Motor is not operating.)
Wave pattern characteristics
Induced electromotive force from the motor turning does
not appear.
Example 2
Cause of problem
Open circuit in the line between the ISC servo and the
engine-ECU.
Wave pattern characteristics
Current is not supplied to the motor coil on the open circuit
side. (Voltage does not drop to 0 V.)
Furthermore, the induced electromotive force waveform
at the normal side is slightly different from the normal
waveform.
Open
circuit
side
Normal
side
MPI –
Troubleshooting
13B-76
IGNITION COIL AND POWER TRANSISTOR
Power transistor control signal
Measurement Method
1.
Disconnect the ignition coil connector, and connect the
special tool (test harness: MB991348) in between. (All
terminals should be connected.)
2.
Connect the analyzer special patterns pickup to terminal
3 of each ignition coil connector in turn.
Alternate Method (Test harness not available)
1.
Connect the analyzer special patterns pickup to
engine-ECU terminal 10 (No. 1 – No. 4), terminal 23 (No.
2 – No. 3) respectively.
Standard Wave Pattern
Observation condition
Function
Special patterns
Pattern height
Low
Pattern selector
Display
Engine r/min
Approx. 1,200 r/min
Standard wave pattern
T: Revolution time corresponding to a crank angle of 180
Compression top dead center
(V)
6
4
2
Power transis-
tor control signal
wave pattern
0
4
2
0
OFF
ON
Dwell section
T1: Time computed by the engine-ECU
Time
T1
θ θ
: Spark
advance
angle
Ignition period
Crank angle
sensor output
wave pattern
T
75
BTDC 5
BTDC
Special
patterns
pickup
Analyzer
MPI –
Troubleshooting
13B-77
Wave Pattern Observation Points
Point: Condition of wave pattern build-up section and maximum voltage (Refer to abnormal wave pattern
examples 1 and 2.)
Condition wave pattern build-up section and maximum
voltage
Probable cause
Rises from approx. 2 V to approx. 4.5 V at the top-right
Normal
2V rectangular wave
Open-circuit in ignition primary circuit
Rectangular wave at power voltage
Power transistor malfunction
Examples of Abnormal Wave Pattern
Example 1
Wave pattern during engine cranking
Cause of problem
Open-circuit in ignition primary circuit
Wave pattern characteristics
Top-right part of the build-up section cannot be seen, and
voltage value is approximately 2 V too low.
Example 2
Wave pattern during engine cranking
Cause of problem
Malfunction in power transistor
Wave pattern characteristics
Power voltage results when the power transistor is ON.
--- Normal wave pattern
2 V
--- Normal wave pattern
V
B
MPI –
On-vehicle Service
13B-78
ON–VEHICLE SERVICE
BASIC IDLE SPEED ADJUSTMENT
NOTE
(1) The standard idling speed has been adjusted by the
speed adjusting screw (SAS) by the manufacturer,
and there should usually be no need for readjustment.
(2) If the adjustment has been changed by mistake, the
idle speed may become too high or the idle speed
may drop too low when loads from components such
as the A/C are placed on the engine. If this occurs,
adjust by the following procedure.
(3) The adjustment, if made, should be made after first
confirming that the spark plugs, the injectors, the idle
speed control servo, the compression pressure, etc.,
are all normal.
1.
Before inspection and adjustment, set the vehicle to the
pre-inspection condition.
2.
Connect the MUT-
II
to the diagnosis connector (16-pin).
NOTE
When the MUT-
II
is connected, the diagnosis control
terminal should be earthed.
3.
Start the engine and run at idle.
4.
Select the item No. 30 of the MUT-
II
Actuator test.
NOTE
This holds the ISC servo at the basic step to adjust the
basic idle speed.
5.
Check the idle speed.
Standard value: 750
±
50 r/min
NOTE
(1) The engine speed may be 20 to 100 r/min lower than
indicated above for a new vehicle [driven
approximately 500 km or less], but no adjustment is
necessary.
(2) If the engine stalls or the engine speed is low even
though the vehicle has been driven approximately 500
km or more, it is probable that deposits are adhered
to the throttle valve, so clean it.
6.
If not within the standard value range, turn the speed
adjusting screw (SAS) to make the necessary adjustment.
7.
Press the MUT-
II
clear key, and release the ISC servo
from the Actuator test mode.
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