Mitsubishi Grandis. Manual - part 782

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI)

13A-379

Wave Pattern Observation Points

Check that cycle time T becomes shorter when the 
engine speed increases.

Examples of Abnormal Wave Patterns

•

Example 1

Cause of problem
Sensor interface malfunction
Wave pattern characteristics
Rectangular wave pattern is output even when 

the engine is not started.

•

Example 2

Cause of problem
Loose timing belt
Abnormality in sensor disk
Wave pattern characteristics
Wave pattern is displaced to the left or right.

INJECTOR
Measurement Method

1. Disconnect the injector connector, and then 

connect the special tool Test harness set 
(MB991658) in between (All terminals should be 
connected).

2. Connect the oscilloscope special patterns pickup 

to terminal No. 2 of the injector connector.

Alternate Method (Test harness not 
available)

1. Connect the oscilloscope special patterns pickup 

to engine-ECU <M/T> or engine-A/T-ECU <A/T> 
terminal No. 1 (When checking the No. 1 
cylinder).

AK305868

40

20

0

(V)

Stepper
motor
control
signal
wave
pattern

The wave pattern
appears for an
instant, but soon
disappears.

Point B
Coil reverse electromotive
force (Approximately 40 V)

Standard wave pattern

Point A
Induced electromotive force
from the motor turning

Time

AB

AK304525

AK203244

AK101807

1

2

AC

Special
patterns
pickup

Oscilloscope

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI)

13A-380

2. Connect the oscilloscope special patterns pickup 

to engine-ECU <M/T> or engine-A/T-ECU <A/T> 
terminal No. 5 (When checking the No. 2 
cylinder).

3. Connect the oscilloscope special patterns pickup 

to engine-ECU <M/T> or engine-A/T-ECU <A/T> 
terminal No. 14 (When checking the No. 3 
cylinder).

4. Connect the oscilloscope special patterns pickup 

to engine-ECU <M/T> or engine-A/T-ECU <A/T> 
terminal No. 21 (When checking the No. 4 
cylinder).

Standard Wave Pattern

Observation conditions

Wave Pattern Observation Points

Point A: Height of solenoid back electromotive force

Point B: Injector drive time

•

The injector drive time will be synchronized with the 

MUT-III tester display.

• When the engine is suddenly raced, the drive 

time will be greatly extended at first, but the drive 
time will soon match the engine speed.

IGNITION COIL AND POWER 
TRANSISTOR
Measurement Method

1. Disconnect the ignition coil connector, and 

connect the special tool Test harness (MB991658) 
in between (All terminals should be connected).

2. Connect the oscilloscope special patterns pickup 

to terminal No. 3 of each ignition coil connector in 
turn.

Function

Special patterns

Pattern height

Variable

Variable knob

Adjust while viewing the 
wave pattern

Pattern selector

Display

Engine

Idle

AK305803

(V)

50

0

Power 
voltage

Solenoid back 
electromotive force
(Approximately 7×10V)

Drive signal: ON

Drive signal: OFF

Point B
Injector drive
time

Point A.

Standard wave pattern

Time

AB

Contrast with standard wave 
pattern

Probable 
cause

Solenoid coil back electromotive 
force is low or doesn’t appear at 
all.

Short in the 
injector solenoid

AKX01605AE

When idling
When racing

AK300345

1 2 3

AB

Special
patterns
pickup

Oscilloscope

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI)

13A-381

Alternate Method (Test harness not 
available)

1. Connect the oscilloscope probe to engine-ECU 

<M/T> or engine-A/T-ECU <A/T> terminal No. 31. 
(When checking the number 1 cylinder.)

2. Connect the oscilloscope probe to engine-ECU 

<M/T> or engine-A/T-ECU <A/T> terminal No. 32. 
(When checking the number 2 cylinder.)

3. Connect the oscilloscope probe to engine-ECU 

<M/T> or engine-A/T-ECU <A/T> terminal No. 35. 
(When checking the number 3 cylinder.)

4. Connect the oscilloscope probe to engine-ECU 

<M/T> or engine-A/T-ECU <A/T> terminal No. 52. 
(When checking the number 4 cylinder.)

Standard Wave Pattern

Observation condition

Wave Pattern Observation Points

Point: When the engine speed increases, verify that 
the power transistor control signal (ignition timing) 
advances.

Examples of Abnormal Wave Patterns

•

Example
Wave pattern during engine cranking

Cause of problem
Open-circuit in ignition primary circuit

Function

Special patterns

Pattern height

Low

Pattern selector

Display

Engine

Approximately. 1,200 
r/min

AK305797

10

0

0

5

(V)

Crank angle
sensor output
wave pattern

Power transistor
control signal
wave pattern

5˚ BTDC

TDC

Ignition timing

OFF

ON

Dwell section

Standard wave pattern

TDC: Top dead centre

2 engine revolutions
(1 camshaft revolution)

AB

AK203246

Normal wave pattern

AD

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI)

13A-382

Wave pattern characteristics
Top-right part of the build-up section cannot be 

seen, and voltage value is approximately 2 V 
too low.

EGR VALVE (STEPPER MOTOR)
Measurement Method

1. Disconnect the EGR valve connector, and 

connect the special tool test harness (MB991658) 
in between.

2. Connect the oscilloscope probe to the EGR 

valve-side connector terminal 1, terminal 3, 
terminal 4 and terminal 6 respectively.

Alternate Method (Test Harness not 
Available)

1. Connect the oscilloscope probe to engine-ECU 

<M/T> or engine-A/T-ECU <A/T> terminal No. 3, 
connection terminal No. 12, connection terminal 
No. 19, and connection terminal No. 26 
respectively.

Standard Wave Pattern

Observation condition

Wave pattern Observation Points

Check that the standard wave pattern appears when 
the EGR control servo is operating.
Point A: Presence or absence of induced 
electromotive force from the motor turning. (Refer to 
the abnormal wave pattern.)

Point B: Height of coil reverse electromotive force

AK303311

1 2 3
4 5 6

AB

Special
patterns
pickup

Oscilloscope

Function

Special patterns

Pattern height

High

Pattern selector

Display

Engine

Ignition switch: OFF 

→ 

ON

AK301251

AK301251

40

20

0

(V)

Stepper
motor
control
signal
wave
pattern

The wave pattern
appears for an
instant, but soon
disappears.

Point B
Coil reverse electromotive
force (Approximately. 40V)

Standard wave pattern

Point A
Induced electromotive force
from the motor turning

Time

AB

Contrast with standard wave 
pattern

Probable 
cause

Induced electromotive force does 
not appear or is extremely small.

Motor is 
malfunctioning

Contrast with standard wave 
pattern

Probable 
cause

Coil reverse electromotive force 
does not appear or is extremely 
small.

Short in the 
coil