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The misfire detection monitor runs during normal engine operating and driving conditions, and is used by the PCM to determine whether the engine is malfunctioning to the point where it is releasing excess pollutants into the atmosphere.
The OBD II system detects misfires on most vehicles by monitoring variations in the speed of the crankshaft through the crankshaft position sensor.
A single misfire will cause a subtle change in the speed of the crank. The PCM tracks each misfire, adding them up and averaging them over time to determine if the rate of misfire is high enough to cause the vehicle to exceed the federal emissions limit.
Whenever crankshaft rotational velocity varies by just 2 percent, one or more misfire codes are stored in the memory of the PCM. If this happens on two consecutive trips, the check engine light will be commanded on to alert the vehicle operator that a misfire problem is occurring.
If the misfire causes the crankshaft speed to vary by more than 10 percent, the check engine light flashes two times a second to warn the vehicle operator that a severe, catalytic converter damaging misfire condition is occurring.
When the misfire detection monitor detects a misfire, the check engine light will flash as the misfire is occurring
The Global Engine misfire detection sensors market accounted for $XX Billion in 2022 and is anticipated to reach $XX Billion by 2030, registering a CAGR of XX% from 2023 to 2030.
Misfire detection with OpenECU – During a normal combustion event, the piston speed is lowest at top dead center on the compression stroke, and is the highest with the piston moving downwards during the power stroke.
The average engine speed for a single engine revolution would lie in between the lowest and the highest instantaneous values. The difference between the lowest and highest engine speeds is significant enough that any deviation from the values expected during normal combustion can be used to detect a misfire event.
If misfire occurs, the crank speed during the power stroke will be significantly lower as there is no downward force being applied on the piston head from combustion of the air fuel mixture. Figure 1 shows how the variation of instantaneous engine speed with crank angle for normal combustion and misfire conditions.
