Misfire Detection Method

Misfire caused by spark failure or combustion failure can be distinct. Spark failures are detected by measuring the time immediate after ignition until the remaining coil energy yields into an oscillation current. Spark failures are caused due insufficient short sparks or no sparks at all. A to short spark is typically caused by short-circuit on the spark plug or an insufficient charged ignition coil. The short spark does not ignite the fuel-air mixture. Hence, no further ionization is produced after the oscillation current from the remaining coil energy.

Fig 1: Insufficient Short Sparks Waveform Characteristic

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In case no spark is produced at all, there is whether the high negative current during the spark neither any further ionization caused by the flame front or combustion process.

Fig 2: Expected Spark Time Chart

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In order to detect misfire caused by combustion failure, the ion current is integrated over the misfire window. The misfire window covers the area of ionization caused by the combustion process and partly the ionization cause by the flame front. If the calculated integral not fulfills a sufficient value according engine load and revs, a combustion failure misfire is detected.

Fig 3: Combustion Failure Waveform

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