Circuit Description

Crankshaft Position (CKP) sensor sends pulses to the PCM as reluctor teeth rotate past the sensor. These pulses are used to synchronize ignition and fuel injector operation. PCM times the interval between each pulse and compares each new time interval with the previous one in order to determine when an excessive change in crankshaft speed has occurred. If crankshaft speed changes are greater than an expected amount, PCM will interpret this as a misfire. If 12 percent or more of the cylinder firing events are misfires, emission levels may exceed standards. PCM monitors blocks of 200 engine revolutions and counts the number of misfires that occur in each block.