Mitsubishi Montero (2004+). Manual - part 395

IGNITION SYSTEM

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ENGINE ELECTRICAL

16-35

WAVEFORM OBSERVATION POINTS
Point A:

The height, length and slope of the spark line (refer to
abnormal waveform examples 1, 2, 3 and 4) show the fol-
lowing trends.

Point B:

SPARK LINE

PLUG
GAP

STATUS OF
ELECT-
RODES

COMPRES-
SION
FORCE

CONCENT-
RATION OF
AIR MIXTURE

IGNITION
TIMING

SPARK PLUG
CABLE

Length

Long

Small

Normal

Low

Rich

Advanced

Leak

Length

Short

Large

Large wear

High

Lean

Retarded

High
resistance

Height

High

Large

Large wear

High

Lean

Retarded

High
resistance

Height

Low

Small

Normal

Low

Rich

Advanced

Leak

Slope

Large

Plug is
fouled

−

AKX00279

SECONDARY
IGNITION
VOLTAGE
WAVE PATTERN

TIME

NO.1 CYLINDER

NO.3 CYLINDER
IGNITION NOISE

NO.6 CYLINDER
IGNITION NOISE

NEUTRAL
SECTION

NO.4 CYLINDER
(WAVE PATTERN
IS DISTURBED)

NO.2 CYLINDER
IGNITION NOISE

NO.5 CYLINDER
IGNITION NOISE

IGNITION SYSTEM

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ENGINE ELECTRICAL

16-36

Number of vibrations in reduction vibration section (Refer to
Abnormal Waveform Example 5)

Point C:

Number of vibrations at beginning of dwell section (Refer to
Abnormal Waveform Example 5)

Point D:

Ignition voltage height (distribution per each cylinder) shows
the following trends.

ABNORMAL WAVEFORMS EXAMPLES
Example 1

• Wave characteristics

Spark line is high and short.

• Cause of problem

Spark plug gap is too large.

Example 2

• Wave characteristics

Spark line is low and long, and is sloping.
Also, the second half of the spark line is distorted. This
could be a result of misfiring.

• Cause of problem

Spark plug gap is too small.

NUMBER OF VIBRATIONS

COIL AND CAPACITOR

Three or more

Normal

Except above

Abnormal

NUMBER OF VIBRATIONS

COIL

− 6 or higher

Normal

Except above

Abnormal

IGNITION
VOLTAGE

PLUG
GAP

CONDITION
OF ELECT-
RODE

COMPRESSION
FORCE

CONCENT-
RATION OF AIR
MIXTURE

IGNITION TIMING

SPARK PLUG
CABLE

High

Large

Large wear High

Lean

Retarded

High resistance

Low

Small

Normal

Low

Rich

Advanced

Leak

AKX00280

AKX00281

IGNITION SYSTEM

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ENGINE ELECTRICAL

16-37

Example 3

• Wave characteristics

Spark line is low and long, and is sloping. However,
there is almost no spark line distortion.

• Cause of problem

Spark plug gap is fouled.

Example 4

• Wave characteristics

Spark line is high and short.
Difficult to distinguish between this and abnormal wave
pattern example 1.

• Cause of problem

Spark plug cable is not properly connected. (Causing a
dual ignition)

Example 5

• Wave characteristics

No waves in wave damping section

• Cause of problem

Layer short in ignition coil.

AKX00282

AKX00283

AKX00284

IGNITION SYSTEM

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ENGINE ELECTRICAL

16-38

IGNITION PRIMARY VOLTAGE WAVE PATTERN
CHECK USING AN OSCILLOSCOPE

M1163004600086

MEASUREMENT METHOD

Required Special Tool:
MB991348: Test Harness Set
1. Disconnect the ignition power transistor connector and

connect the test harness set of the special tool (MB991348)
in between. All terminals should be connected.

2. When observing the number 1

− 4 cylinder group, connect

the primary pickup of the oscilloscope probe to ignition
power transistor side connector terminal (13).
For the number 2

− 5 cylinder group, connect to terminal

(12) and for the number 3

− 6 cylinder group, connect to

terminal (11).

3. Ground the primary pickup ground terminal.
4. Clamp the spark plug cable with the trigger pickup.

NOTE: Clamp the spark plug cable of cylinder number 1, 3
or 5 which belongs to the same group as the cylinder to
which the primary pickup is connected.
NOTE: The wave pattern of any cylinder in the same group
appears from the left side of the screen.

STANDARD WAVE PATTERN

Observation conditions

FUNCTION

SECONDARY

Pattern height

High (or low)

Pattern selector

Raster

Engine speed

Curb idle speed

AKX00285

11 12 13

PRIMARY
PICKUP

OSCILLOSCOPE

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