Calais L4-151 2.5L VIN U TBI (1989)
Crankshaft Position Sensor: Description and Operation
Typical DIS Crankshaft Sensor
This crankshaft sensor is mounted remotely on the bottom side of the ignition module. This sensor protrudes into the block, within approximately 0.050"
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.
Based on the crank pulses, the DIS module sends reference signals to the ECM which are used to indicate crankshaft position and engine speed. The
ignition module will continue to send these reference pulses to the ECM at a rate of one for each 180° or crankshaft rotation. The ECM will activate the
fuel injector based on the recognition of every other reference pulse beginning at a crankshaft position of 120° after top dead center.
By comparing the time between pulses, the DIS module can recognize the pulse representing the seventh slot or "sync pulse," which starts the calculation
of the ignition coil sequence. The second crank pulse following the "sync pulse" signals the "DIS" module to fire the #2/3 ignition coil and the fifth crank
pulse signals the module to fire the #1/4 ignition coil.