Oscilloscope Pattern Diagnostics (Spark Plug Faults)

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For evaluation of sparking period at idle, voltage peak No. 1 indicates normal ignition voltage peak. Spark plug is okay. If ignition voltage peak (voltage peak No. 2) is low, electrode gap is small. If ignition voltage peak (voltage peak No. 3) is high, electrode gap is too large. See Fig 1.
For normal combustion and spark plug, see Fig 2. If combustion period is long, electrode gap is small. See Fig 3. If spark period is short, electrode gap is large. See Fig 4.

Fig 1: Identifying Oscilloscope Patterns (Spark Period At Idle Speed)
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Fig 2: Identifying Oscilloscope Patterns (Normal Combustion & Spark Plug)
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Fig 3: Identifying Oscilloscope Patterns (Long Combustion Period)
Courtesy of BMW OF NORTH AMERICA, INC.

Fig 4: Identifying Oscilloscope Patterns (Short Spark Period)
Courtesy of BMW OF NORTH AMERICA, INC.