Mitsubishi Montero (2002-2004). Manual — part 575

INSPECTION PROCEDURE USING AN OSCILLOSCOPE

TSB Revision

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

13Ab-57

Point B: Height of coil back electromotive force

.

Examples of Abnormal Wave Patterns
Example 1
Cause of problem

• Malfunction of motor. (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 EGR valve and the

PCM.

Wave pattern characteristics

• Current is not supplied to the motor coil on the open cir-

cuit side. (Voltage does not drop to 0 volt.) Furthermore,
the induced electromotive force wave pattern at the nor-
mal side is slightly different from the normal wave pat-
tern.

IGNITION COIL AND IGNITION POWER
TRANSISTOR

Required Special Tool:

• MB991348: Test Harness Set

.

Measurement Method
1. Disconnect the ignition coil connector, and connect test

harness special tool, MB991348, in between. (All terminals
should be connected.)

2. Connect the oscilloscope probe to ignition coil connector

terminal No. 3.

.

Alternate method (Test harness not available)
Connect the oscilloscope probe to PCM terminals No. 31 (for

number 1

− number 4), terminal No. 35 (for number 2 −

number 5) , terminal No. 44 (for number 3

− number 6)

respectively.

CONTRAST WITH
STANDARD WAVE
PATTERN

PROBABLE CAUSE

Coil reverse electromotive
force does not appear or is
extremely small

Short in the coil

AKX01608 AB

AKX01609

OPEN
CIRCUIT
SIDE

NORMAL
SIDE

AB

AK102984AB

1

2

3

IGNITION COIL
CONNECTOR

OSCILLOSCOPE

MB991348

INSPECTION PROCEDURE USING AN OSCILLOSCOPE

TSB Revision

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

13Ab-58

Standard Wave Pattern

Wave Pattern Observation Points
Point: Condition of wave pattern build-up section and maximum

voltage (Refer to abnormal wave pattern examples 1 and 2.

.

Observation condition

Function

Special pattern

Pattern height

Low

Pattern selector

Display

Engine r/min

Approximately 1,200 r/min

CONDITION OF WAVE
PATTERN BUILD-UP
SECTION AND MAXIMUM
VOLTAGE

PROBABLE CAUSE

Rises from approximate 2
volts to approximate 4.5 volts
at the top-right

Normal

2-volt rectangular wave

Open-circuit in ignition primary
circuit

Rectangular wave at power
voltage

Ignition power transistor
malfunction

(V)

6

4

2

0

6

4

2

0

AK201316

75˚BTDC

5˚BTDC

ON

TIME

T

AB

θ

T1

OFF

CRANKSHAFT
POSITION
SENSOR OUTPUT
WAVE PATTERN

IGNITION POWER
TRANSISTOR
CONTROL SIGNAL
WAVE PATTERN

Standard wave pattern

T: REVOLUTION TIME CORRESPONDING

TO A CRANK ANGLE OF 180˚
COMPRESSION TOP DEAD CENTER

θ

: SPARK

ADVANCE
ANGLE

IGNITION PERIOD

DWELL
SECTION

T1: TIME COMPUTED BY THE PCM

INSPECTION PROCEDURE USING AN OSCILLOSCOPE

TSB Revision

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

13Ab-59

Examples of Abnormal Wave Patterns
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 volts too low.

Example 2 (Wave pattern during engine cranking)

• Cause of problem

Malfunction in ignition power transister

• Wave pattern characteristics

Power voltage results when the ignition power transistor is
ON.

AKX01612

NORMAL WAVE
PATTERN

2V

AB

AKX01613

BATTERY
POSITION
VOLTAGE

NORMAL WAVE
PATTERN

AB

NOTES