Misfire Algorithm Processing (2018)

The F250-F750 6.7L engine uses a misfire monitor that operates across much of the engine speed and torque range of the vehicle. The misfire monitor evaluates crankshaft angular acceleration in terms of cylinder "segments" representing the arc in which each cylinder fires. Each cylinder segment is 90° in length (720° / 8 cylinders = 90°). The monitor compares angular acceleration of the crankshaft from one cylinder event to the next. For various powertrain configurations and transmissions statuses, there are threshold maps populated of the minimum segment-to-segment response that indicates a misfire event. These maps are populated from real misfire conditions throughout an engine map. Once a threshold is reached, it is flagged a misfire event and counted. An interval is 4 complete segments of 1, 000 crankshaft revolutions. If the summation of misfires reaches 5% of the total number of combustion events in any 4 complete segment interval, a fault is then set for misfire. In the case of cold starting there is a special "no glow" function. This function evaluates the glow lamp status. In the event that an end operator does not allow for sufficient time glow, the monitor is temporarily disabled. This is to ensure no misfire detection when the engine is unstable from a non-complete or no glow. Once the proper thresholds are met after a no glow, the misfire monitor is reinstated to its normal operation.

The 3.2L diesel uses a similar algorithm to the one described above except that there are fewer cylinders.