Oscilloscope Pattern Diagnostics

Evaluate sparking period and ignition voltage peaks at idle. Voltage peak No. 1 indicates normal combustion period. Voltage peak No. 2 indicates normal ignition voltage peak. Ignition system is okay. See Fig 1.
If scope indicates a long sparking period (voltage peak No. 1) with ignition voltage (voltage peak No. 2), low compression is present. If sparking period is fluctuating, spark plug is fouled. See Fig 2.
A short sparking period (voltage peak No. 1) with high ignition voltage peak (voltage peak No. 2) or a constant but short sparking period, indicates a defective ignition lead. See Fig 3.
During evaluation of ignition voltage peaks and attenuation process at idle, if scope indicates a beginning of attenuation process with normal peaks upwards and downwards (voltage peak No. 1), or attenuation process is greatly shortened (voltage peak No. 2), ignition coil is defective. If there is an absence of initial downwards attenuation (voltage peak No. 3), ignition coil is defective. See Fig 4.
During evaluation of sparking voltage at idle, normal combustion period is indicated by voltage peak No. 1. Normal attenuations to sparking voltage line is indicated by voltage peak No. 2. Ignition coil is okay. See Fig 5. If shorter sparking period is indicated (voltage peak No. 1) or attenuation to sparking voltage line is only slight (voltage peak No. 2), ignition coil is defective. See Fig 6. If sparking period is much shorter (voltage peak No. 1) or attenuation to sparking voltage line is absent (voltage peak No. 2), ignition coil is defective. See Fig 7. If there is no sparking voltage line, ignition coil is defective. See Fig 8.
During evaluation of combustion voltage line at a raised engine speed, voltage peak No. 1 indicates normal combustion period. Voltage peak No. 2 indicates normal attenuations to sparking voltage line. Ignition coil is okay. See Fig 9. A shorter sparking period (voltage peak No. 1) and if attenuations to sparking voltage line is only slight (voltage peak No. 2), then ignition coil is defective. See Fig 10. If combustion period (voltage peak No. 1) is normal or attenuations to sparking voltage line are absent (voltage peak No. 2), ignition coil is defective. See Fig 11.

Fig 1: Identifying Oscilloscope Pattern (Normal Pattern)

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Fig 2: Identifying Oscilloscope Pattern (Low Compression Or Fouled Spark Plug)

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Fig 3: Identifying Oscilloscope Pattern (Defective Ignition Lead)

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Fig 4: Identifying Oscilloscope Pattern (Ignition Coil Defective)

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Fig 5: Identifying Oscilloscope Pattern (Voltage Line At Idle - Ignition Coil Okay)

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Fig 6: Identifying Oscilloscope Pattern (Voltage Line At Idle - Ignition Coil Defective)

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Fig 7: Identifying Oscilloscope Pattern (Short Spark Period - Ignition Coil Defective)

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Fig 8: Identifying Oscilloscope Pattern (No Spark Voltage - Ignition Coil Defective)

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Fig 9: Identifying Oscilloscope Pattern (Engine Speed Above Idle - Ignition Coil Okay)

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Fig 10: Identifying Oscilloscope Pattern (Engine Speed Above Idle - Ignition Coil Defective - 1 Of 2)

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Fig 11: Identifying Oscilloscope Pattern (Engine Speed Above Idle - Ignition Coil Defective - 2 Of 2)

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