Mitsubishi Space Star. Manual - part 72

 

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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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