Waste Spark

Waste spark systems have companion cylinders that share one ignition coil. When the ignition coil fire one cylinder will be neat top dead center of the compression stroke and the other cylinder will be at the beginning of the exhaust stroke. In a typical engine, it only requires about 2 to 3 kV (2,000 to 3,00 volts) to jump across the spark plug gap of the cylinder in the exhaust stroke. The remaining voltage available for firing the cylinder on the compression stroke is about 8 to 12 kV. This system may allow more exhaust efficiency by igniting any remaining fuel in the exhaust and saves money by achieving ignition efficiency using four coils for a V8 engine versus the eight coils that would be required for coil on plug.

Waste Spark Video

The image below is of a waste spark wiring diagram. The coils are paired. Some manufacturers separate the ignition system transistors that trigger the primary windings into an ignition control module (ICM). Others have all of the coil firing or triggering of the coils take place in the main computer (PCM). The triggering of ignition coils causes voltage spikes that create heat. Heat eventually can cause the triggering transistors to fail in either the ICM or PCM.

The voltage produced by an ignition coil produces a primary and secondary waveform. The examination of a coil waveform can help diagnose ignition system, fuel system (how rich or lean an engine is running).

Below is a normal secondary coil waveform.

Below is a parade pattern of all of the secondary waveforms. One cylinder is misfiring. There is also a lot of variation in the other cylinders. The peak voltages vary, and the spark line duration varies. The secondary waveform indicates that the car is running poorly.

Below is an image of coil current in a parade pattern. A parade pattern displays all of the cylinders. The current generated by an ignition coil is one of the best tests to determine if the coil is generating enough current to fire the spark plug. This screen capture shows normal waveforms.

The image below displays coils that are not working correctly. The total amperage is lower and the coil saturation time varies compared to the coils that are normal.