Crankshaft Position Sensor: Description and Operation

Crankshaft Sensor IDI:

PURPOSE
The crankshaft sensor provides a signal through the Integrated Direct Ignition (IDI), which the ECM/PCM uses as reference to calculate rpm and crankshaft position.

OPERATION
Based on the crank sensor pulses, the ignition module sends 2X reference signals to the ECM/PCM which are used to indicate crankshaft position and engine speed. The ignition module continues to send these reference pulses at a rate of one per each 180° of crankshaft rotation. This signal is called the 2X reference because it occurs 2 times per crankshaft revolution.

The ignition also sends a second, 1X reference signal to the ECM/PCM which occurs at the same time as the "sync pulse" from the crankshaft sensor. This signal is called the 1X reference because it occurs 1 time per crankshaft revolution. The 1X reference and the 2X reference signals are necessary for the ECM/PCM to determine when to activate the fuel injectors.

By comparing the time between pulses, the ignition module can recognize the pulse representing the seventh slot or "sync pulse" which starts the calculation of the ignition coil sequencing. The second crank pulse following the "sync pulse" signals the ignition module to fire the #2-3 ignition coil, and the fifth crank pulse signals the ignition module to fire the #1-4 ignition coil.

LOCATION AND CONSTRUCTION
This crankshaft sensor is mounted remotely from the ignition module. This sensor protrudes into the block, within approximately .050" of the engine crankshaft reluctor. The reluctor is a special wheel cast into the crankshaft with seven slots cast into it, six of which are evenly spaced 60° apart. A seventh slot is spaced 10° from one of the other slots and serves to generate a "sync pulse." As the reluctor rotates as part of the crankshaft, the slots change the magnetic field of the sensor, creating an induced voltage pulse.