Mitsubishi Eclipse / Eclipse Spyder (2000-2002). Service and repair manual - part 191

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI) <2.4L ENGINE>

13A-463

Measurement Method
1. Disconnect the idle air control motor connector, and connect 

the test harness special tool (MB991709) in between. (All 
terminals should be connected.)

2. Connect the oscilloscope probe to the idle air control motor 

connector terminal 1, terminal 3, terminal 4 and terminal 6, 
respectively.

Alternate method (Test harness not available)

1. Connect the oscilloscope probe to ECM <M/T> or PCM <A/

T> terminals 14, 15, 28 and 29.

Standard Wave Pattern

Wave Pattern Observation Points

1. Check that the standard wave pattern appears when the 

idle air control motor is operating. 
Point A:

Presence or absence of induced electromotive force from the 

motor turning. (Refer to abnormal wave pattern.)

Observation conditions

Function

Special pattern

Pattern height

High

Pattern selector

Display

Engine condition

Turn the ignition switch from 
"OFF" to "ON" (without 
starting the engine).

While the engine is idling, 
turn the A/C switch to "ON."

Immediately after starting the 
warm the engine 
(approximately one minute).

AKX01606

6

3

1 2
4 5

OSCILLOSCOPE

OSCILLOSCOPE PLOBE

AKX01606AB

AKX01607 AB

(V)

30

20

10

0

IAC
MOTOR
CONTROL
SIGNAL
WAVE
PATTERN

THE WAVE PATTERN
APPEARS FOR AN
INSTANT, BUT SOON
DISAPPEARS.

POINT B COIL RE-
VERSE ELECTRO-
MOTIVE FORCE
(APPROXIMATELY
3 x10 V)

POINT AN INDUCED
ELECTROMOTIVE
FORCE FROM THE
MOTOR TURNING

TIME

Standard wave pattern

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI) <2.4L ENGINE>

13A-464

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 idle air control motor 
and the ECM <M/T> or PCM <A/T>.

•

Wave pattern characteristics
Current is not supplied to the motor coil on the open circuit 
side. (Voltage does not drop to 0 volt.) Furthermore, the 
induced electromotive force wave pattern at the normal side 
is slightly different from the normal wave pattern.

IGNITION COIL AND IGNITION POWER 
TRANSISTOR

Required Special Tool:
MB991348: Test Harness Set

CONTRAST WITH 
STANDARD WAVE 
PATTERN

PROBABLE CAUSE

Induced electromotive force 
does not appear or is 
extremely small

Malfunction of motor

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

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI) <2.4L ENGINE>

13A-465

Measurement Method
1. Disconnect the 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 3.

Alternate method (Test harness not available)

1. Connect the oscilloscope probe to ECM <M/T> or PCM <A/

T> terminal 11.

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 conditions

Function

Special pattern

Pattern height

Low

Pattern selector

Display

Engine r/min

Approximately 1,200 r/min

AK000067

1 2 3 4 5 6 7

OSCILLOSCOPE

DISTRIBUTOR 
CONNECTOR

OSCILLO

SCOPE

PLOBE

AB

AK000069

CRANKSHAFT

POSITION

SENSOR OUTPUT

WAVE PATTERN

(REFERENCE)

IGNITION POWER

TRANSISTOR

CONTROL SIGNAL

WAVE PATTERN

POINT:

WAVE BUILD-UP

SECTION

Standard wave pattern

θ

θ 

: SPARK ADVANCE ANGLE

ON

DWELL SECTION

TIME

OFF

T

T : CRANKSHAFT ANGLE (120˚)

COMPRESSION
TOP DEAD CENTER

0

2

4

6

0

2

4

6

(V)

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI) <2.4L ENGINE>

13A-466

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 transistor

•

Wave pattern characteristics
Power voltage results when the ignition power transistor is 
ON.

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

AKX01612

NORMAL WAVE
PATTERN

2V

AB

AKX01613

BATTERY
POSITION
VOLTAGE

NORMAL WAVE
PATTERN

AB