Oscilloscope Patterns and Waveforms

INSPECTION PROCEDURE USING AN OSCILLOSCOPE

IGNITION COIL AND IGNITION POWER TRANSISTOR

Required Special Tools:
- MB991658: Test Harness
- MB992110: Power Plant ECU Check Harness.

Measurement Method







1. Disconnect the ignition coil connector, and connect test harness special tool (MB991658) between the separated connector. (All terminals should be connected.)
2. Connect the oscilloscope probe to ignition coil connector terminal No. 2.

Alternate method







1. Disconnect all ECM connectors. Connect the check harness special tool (MB992110) between the separated connectors.







2. Connect the oscilloscope probe to each check harness connector terminal to analyze each cylinder:
- Terminal No. 4 for the number 1 cylinder.
- Terminal No. 5 for the number 2 cylinder.
- Terminal No. 20 for the number 3 cylinder.
- Terminal No. 21 for the number 4 cylinder.










Wave Pattern Observation Points
Point: The power transistor control signal (ignition timing) is advanced when the engine speed is increased.







Examples of Abnormal Wave Patterns







Example 1 (Wave pattern during engine cranking)
Cause of problem
- Open-circuit in ignition primary circuit

Wave pattern characteristics
- Voltage value is too low.