Oscillograms of ignition coils from different manufacturers

Evaluation Of Ignition Voltage Peaks And Decay Characteristics At Idle Speed 

Make: Bremi

1. 1.  Normal ignition voltage spikes (6000-9000 V)
2. 2.  Normal start of attenuation processes

Make: Beru

1. 3.  Normal ignition voltage peak
2. 4.  High initial level of attenuation processes

Make: May & Christe

1. 5.  Normal ignition voltage peak
2. 6.  Low initial level of attenuation processes

Make: Bosch

1. 7.  Low ignition voltage peak
2. 8.  Normal start of attenuation processes

Note:  At high speeds, the ignition voltage peak falls very markedly relative to the peaks on units from other ignition coil manufacturers.

Evaluation Of Combustion Voltage Characteristics At Raised Engine Speed Of Approx. 2500 RPM 

Make: Bremi

Fig 2: Evaluation Of Different Ignition Coils At 2500 RPM (Bremi)
Courtesy of BMW OF NORTH AMERICA, INC.
1. 1.  Normal oscillation of the combustion voltage curve
2. 2.  Normal combustion period
3. 3.  3 to 4 attenuations

Make: Beru

Fig 3: Evaluation Of Different Ignition Coils At 2500 RPM (Beru)
Courtesy of BMW OF NORTH AMERICA, INC.
1. 1.  Normal oscillation of the combustion voltage curve
2. 2.  Normal combustion period
3. 3.  At least 3 decay oscillations

Make: May & Christe

Fig 4: Evaluation Of Different Ignition Coils At 2500 RPM (May & Cristie)
Courtesy of BMW OF NORTH AMERICA, INC.
1. 1.  No oscillation on combustion voltage curve
2. 2.  Normal combustion period
3. 3.  At least 5 decay oscillations

Make: Bosch

Fig 5: Evaluation Of Different Ignition Coils At 2500 RPM (Bosch)
Courtesy of BMW OF NORTH AMERICA, INC.
1. 1.  Normal oscillation of the combustion voltage curve
2. 2.  Long combustion period
3. 3.  At least 3 decay oscillations