IGNITION SECONDARY VOLTAGE WAVEFORM CHECK USING AN OSCILLOSCOPE <4G6-SOHC, 4G6-DOHC>

[16] ENGINE ELECTRICAL - - IGNITION SYSTEM - ON-VEHICLE SERVICE - IGNITION SECONDARY VOLTAGE WAVEFORM CHECK USING AN OSCILLOSCOPE <4G6-SOHC, 4G6-DOHC>

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MEASUREMENT METHOD

Clamp the secondary pickup around the spark plug cable.

NOTE:

The peak ignition voltage will be reversed when the spark plug cables No. 2 and No. 4, or No. 1 and No. 3 cylinders are clamped.

Because of the two-cylinder simultaneous ignition system, the waveforms for two cylinders in each group appear during waveform observation (No. 1 cylinder - No. 4 cylinder, No. 2 cylinder - No. 3 cylinder). However, waveform observation is only applicable for the cylinder with the spark plug cable clamped by the secondary pickup.

Identifying which cylinder waveform is displayed can be difficult. For reference, remember that the waveform of the cylinder attached to the secondary pickup will be displayed as stable.

Clamp the spark plug cable with the trigger pickup.

NOTE: Clamp the trigger pickup to the same spark plug cable clamped by the secondary pickup.

STANDARD WAVEFORM

Observation Conditions
Function	Secondary
Pattern height	High (or Low)
Pattern selector	Raster
Engine revolutions	Curb idle speed

Observation Conditions (The only change from above condition is the pattern selector.)
Pattern selector	Display

WAVEFORM OBSERVATION POINTS

Point A: The height, length and slope of the spark line show the following trends (Refer to abnormal waveform examples, 1, 2, 3 and 4).
Spark line		Plug gap	Condition of electrode	Compression force	Concentration 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	-	-	-	-

Point B: Number of vibration in reduction vibration section (Refer to abnormal waveform example 5)
Number of vibrations	Coil and condenser
3 or more	Normal
Except above	Abnormal

Point C: Number of vibrations at beginning of dwell section (Refer to abnormal waveform example 5)
Number of vibrations	Coil
5 - 6 or higher	Normal
Except above	Abnormal

Point D: Ignition voltage height (distribution per each cylinder) shows the following trends.
Ignition voltage	Plug gap	Condition of electrode	Compression force	Concentration of air mixture	Ignition timing	Spark plug cable
High	Large	Large wear	High	Lean	Retarded	High resistance
Low	Small	Normal	Low	Rich	Advanced	Leak

EXAMPLES OF ABNORMAL WAVEFORMS

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.

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 waveform example 1.

Cause of problem

Spark plug cable is nearly falling off (Causing a dual ignition).

Example 5

Wave characteristics

No waves in wave damping section.

Cause of problem

Layer short in ignition coil.

[16] ENGINE ELECTRICAL - - IGNITION SYSTEM - ON-VEHICLE SERVICE - IGNITION SECONDARY VOLTAGE WAVEFORM CHECK USING AN OSCILLOSCOPE <4G6-SOHC, 4G6-DOHC>

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