Early Models

Engine Speed Sensor (CPS):

The engine speed sensor (Crankshaft Position Sensor -- CPS) provides an input signal to the Engine Control Unit (ECU) on crankshaft position and engine speed by detecting the flywheel pulse ring teeth as they pass by the sensor. The CPS is mounted to the torque converter drive plate housing and is non-adjustable.

Engine Speed Sensor And Drive Plate:

The flywheel pulse ring has three trigger notches, spaced 120° apart, with 20 small teeth between each trigger notch. Each of the large trigger notches is located 12 small teeth prior to Top Dead Center (TDC) of the corresponding pistons. From the flywheel speed and trigger notch signals, the CPS senses engine speed and crankshaft angle position.
As a tooth and notch pass the magnetic core of the speed sensor, a voltage is induced in the sensor pick-up coil winding. The induced voltage signals allow the ECU to count the teeth as they pass by the speed sensor. When the sensor reaches a trigger notch, it causes a slight delay between the voltage signals. This delay alerts the ECU that a piston will be at TDC 12 voltage signals later. The ECU uses this information to control spark and fuel injection timing for each cylinder.