Mitsubishi Colt Ralliart. Manual — part 757

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI) <4G1>

13B-353

Standard Wave Pattern

Observation condition

Description of Wave Pattern

• The camshaft position sensor detects the com-

pression top dead center of each cylinder.
Observing this signal as well as other control sig-
nals simultaneously allows cylinder identification
to be achieved.

• The crank angle sensor detects the crank angle

of each cylinder. 72 crank angle sensor high sig-
nals (including missing tooth) are output at equal
spaces per two revolutions of the engine.

Wave Pattern Observation Points

• Check that the wave pattern becomes shorter

when the engine speed increases.

Function

Special patterns

Pattern height

Low

Pattern selector

Display

Engine

Idle

AK204111AC

(V)

5

0

5

0

No. 1TDC

No. 3TDC

No. 4TDC

No. 2TDC

time

Standard wave pattern

Crank angle
sensor output
wave pattern

Camshaft position
sensor output
wave pattern

2 engine revolutions
(1 camshaft revolution)

TDC: Top dead centre

Main

Index

Group

TOC

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI) <4G1>

13B-354

Examples of Abnormal Wave Patterns

•

Example 1

Wave pattern characteristics
Rectangular wave pattern is output even when the
engine is not started.

Cause of problem
Sensor interface malfunction

•

Example 2

Wave pattern characteristics
Wave pattern shifts left and right frequently.

Cause of problem
Loose timing belt
Abnormality in sensor disk

INJECTOR
Measurement Method

1. Disconnect the injector connector and connect the

special tool test harness (MB991658) in between
(All terminals should be connected).

2. Connect the probe of the oscilloscope to injector

connector terminal No. 2.

Alternate Method (Test harness not
available)

1. Disconnect the engine-ECU connector and

connect the special tool Power plant ECU check
harness (MB991987) in between.

2. Connect the oscilloscope special patterns pickup

to engine-ECU terminal No. 8 (When checking the
No. 1 cylinder).

3. Connect the oscilloscope special patterns pickup

to engine-ECU terminal No. 9 (When checking the
No. 2 cylinder).

4. Connect the oscilloscope special patterns pickup

to engine-ECU terminal No. 23 (When checking
the No. 3 cylinder).

5. Connect the oscilloscope special patterns pickup

to engine-ECU terminal No. 24 (When checking
the No. 4 cylinder).

AK304525

AK203244

AK101807

1

2

AC

Special
patterns
pickup

Oscilloscope

Main

Index

Group

TOC

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI) <4G1>

13B-355

Standard Wave Pattern

Observation conditions

Description of Wave Pattern

• Normally the power voltage is applied, and when

there is a signal from the engine-ECU, the volt-
age drops to near 0 V only for the drive signal
time.

• When the signal from the engine-ECU is turned

off, the peak of the voltage appears by the back
electromotive force of the coil, and the voltage
returns to the power voltage.

• Injector drive time: Fuel injection time determined

by the engine-ECU according to output values of
various sensors. Injector drive time = effective
injection time + ineffective injection time (ineffec-
tive injection time: Corrects operation delay
caused by a drop in the power voltage)

• Back electromotive force of solenoid coil: When

the signal from the engine-ECU is turned off, a
back electromotive force is generated in the
injector coil (approximately 65

− 75 V).

• Power voltage: When there is no signal from the

engine-ECU, the power voltage is applied. When
this power voltage is low, the ineffective injection
time becomes long, and the drive time also
becomes long.

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 M.U.T.-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.

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 does not appear at
all.

Short in the
injector solenoid

AKX01605AE

When idling
When racing

Main

Index

Group

TOC

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI) <4G1>

13B-356

IGNITION COIL AND POWER TRANSIS-
TOR
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 probe of the oscilloscope to ignition

coil connector terminal No. 3.

3. To check the ignition advance condition, observe

the crank angle sensor output signal
simultaneously.

Alternate Method (Test harness not
available)

1. Disconnect the engine-ECU connector and

connect the special tool Power plant ECU check
harness (MB991987) in between.

2. Connect the oscilloscope probe to engine-ECU

terminal No. 10 (When checking the number 1
cylinder.)

3. Connect the oscilloscope probe to engine-ECU

terminal No. 25 (When checking the number 2
cylinder.)

4. Connect the oscilloscope probe to engine-ECU

terminal No. 40 (When checking the number 3
cylinder.)

5. Connect the oscilloscope probe to engine-ECU

terminal No. 55 (When checking the number 4
cylinder.)

Standard Wave Pattern

Observation condition

AK000845

1 2 3

AC

Ignition coil
connector

Oscilloscope

Function

Special patterns

Pattern height

Low

Pattern selector

Display

Engine

Idle

AK204112

Standard wave pattern

Crank angle
sensor output
wave pattern

Power transistor
control signal
wave pattern

TDC: Top dead centre

AC

2 engine revolutions
(1 camshaft revolution)

Ignition timing

Dwell section

0

10

OFF

ON

5˚ BTDC

(V)

TDC

0

5

Main

Index

Group

TOC