12 13 ... Normal oscillogram (M, S, W engines only)

start of ignition voltage peak
Level of ignition voltage
Level of combustion voltage
Period of combustion
Combustion curve characteristics
Start of decay process
Termination oscillations

Fig 1: Terminal Voltage Normal Oscillogram Chart
Courtesy of BMW OF NORTH AMERICA, INC.

Secondary voltage patterns, beside one another:

Evaluation of ignition voltage peaks at idle speed (this example shows an engine with 4 cylinders).

NOTE: The display of ignition voltage spikes is approx. 20-25% lower than the real value.

The uniformity of all cylinders to each other is more important than the height of ignition voltage peaks.

Differences of 3000 ... 4000 V are permitted.

Fig 2: Secondary Voltage Patterns Graph - Ignition Voltage Peaks At Idle Speed

Courtesy of BMW OF NORTH AMERICA, INC.

Evaluation of ignition voltage peaks at increased speed of approx. 2000 RPM (this example shows an engine with 4 cylinders).

Fig 3: Secondary Voltage Patterns Graph - Ignition Voltage Peaks At Increased Speed

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Secondary voltage diagrams, superimposed:

Evaluation of combustion characteristics curve and decay characteristics at idle speed (this example shows a 4-cylinder engine).

Fig 4: Secondary Voltage Diagrams - Superimposed

Courtesy of BMW OF NORTH AMERICA, INC.

Secondary voltage diagrams, consecutive:

NOTE: Only the major differences in the ignition voltage patterns are revealed by this method of comparison.

The identified fault must be allocated to the relevant cylinder using the secondary voltage representation forms next to/on top of each other.

Fig 5: Secondary Voltage Diagrams - Consecutive

Courtesy of BMW OF NORTH AMERICA, INC.