Misfire Detection Monitor - Transit

The engine uses a Hall effect crankshaft position (CKP) sensor that processes the edges of a stamped target wheel mounted on the crankshaft. The software gets an edge every set number of degrees and these edges are used for fuel injection timing, fuel quantity control and the calculation of engine speed. A software algorithm corrects for irregularities of the teeth of the target wheel to improve crankshaft signal resolution. A second Hall effect sensor processes the edges of the lobed camshaft target. The camshaft position signal and the window of missing teeth on the crankshaft target wheel indicate correct camshaft to crankshaft position for correct cylinder timing.

The misfire monitor collects blocks of data consisting of a set of crankshaft rotations. Upon achieving the correct entry conditions for the misfire monitor, the first block of rotations is discarded to ensure stable idle operation. All subsequent blocks of data are counted unless vehicle conditions change such that the entry conditions are no longer satisfied. In this case, any data in the current partial block are discarded, along with the data from the block immediately prior, as stable idle cannot be ensured for these data. The misfire monitor completes once a set number of blocks have been collected and a concern is reported if the number of misfire events for a specific cylinder is greater than a calibrated threshold. Certain engine operating parameters are monitored to ensure misfire operates in a region that yields accurate misfire results.