Crankshaft Position Sensor: Description and Operation

Crankshaft Position Sensor - Location View:

The M5.2 continues to utilize two inductive pulse sensors for crankshaft speed and reference position input signals, What has changed is the installed location and the type of trigger wheel.

The new incremental wheel is incorporated on the flex plate at the rear of the engine. The trigger wheel teeth are larger for better detection purposes. However, the wheel continues to have 58 teeth with a gap of two missing teeth, for the TDC reference point.

The sensors are mounted in the bell housing at a 60 degree angle offset. Each DME control module monitors its respective sensor input for speed (RPM) and reference position.

Due to the new EPA requirements for emission control monitoring (OBD-II), the speed/reference sensors also serve as the input signal for misfire detection.

MISFIRE DETECTION OPERATION
The DME control modules are programmed to monitor the frequency of the AC sine wave pattern produced by the sensors. Each ignition pulse produces a corresponding power (or torque) thrust on the crankshaft.

The DME monitors these power strokes based on the speed and regularity of the wave pattern. If a cylinder misfires, the wave pattern changes, and the DME registers this as a misfire.

The misfiring cylinder is identified based on the camshaft cylinder ID and crankshaft position sensor inputs.

With engine speeds over 3,000 RPM the crankshaft speed is too fast for the control modules to reliably detect a misfire by crankshaft monitoring alone. Each DME control module also monitors a secondary shunt resistor to recognize secondary ignition failure.




INCREMENTAL GEAR WHEEL GENERATED SIGNAL ADAPTATION
Though the incremental gear wheel is a precisely machined component of the engine, slight tolerance differences between each gear tooth are learned by the DME and memorized.

This self learned adaptation period occurs when the engine is decelerating and the DME is in deceleration cutoff. Misfire detection is not required within this period of engine operation.

The adaptation by DME allows the misfire detection function to become more precise as the vehicle is driven.