klr650 cam position sensorThe cam position sensor in combination with a trigger on the crank is required to help the Engine Control Unit (ECU) figure out where in the 4 cycles it is.

It was decided to fit a 5 volt three wire Hall Affect Cam Position Sensor on the valve cover. A sensor adapter boss was installed in such a way that it would allow for the easy removal of the valve cover. Most automotive based Hall Affect Sensors are fairly large but after a little research a small Hall Affect Cam Position Sensor that would do the job was found.  The sensor would be triggered by the intake cam lobe.

What is  a Hall Affect Sensor

A Hall effect sensor is a transducer that varies its output voltage in response to a magnetic field. Hall effect sensors are used for positioning, speed detection, and proximity switching. The Hall Affect Sensor produces a squire wave.

Why the need for a cam position sensor.

For the camshaft to complete one full rotation of 360 degrees the crankshaft has to do two full rotations or 720 degrees, a 2:1 ratio. Because of this  2:1 turn ratio between the crank and the camshaft, a trigger placed on the cam will serve as a reliable place holder to determine exactly where the crank is in the 4 engine cycles.

A trigger signal from the cam position sensor resets the count bit in the ECU to zero. The ECU then starts to count time intervals. The ECU is programed to know that after a predetermined time count the piston is at top dead center. (TDC) Based on the cam trigger and a crank trigger the ECU can therefore determine with absolute accuracy where the piston is during the four stroke cycle.