Mercury Optimax Diagnostic Guide., Page 9Get this manual
OPTIMAX DIAGNOSTIC GUIDE
Procedure 6
CRANK POSITION SENSOR (20012002)
The crank position sensor (CPS) supplies the ECM with crank position information and engine speedIf the sensor should fail the engine will stop runningSome crank position sensors may have had the sensor magnet positioned off-center in the sensor housingThis could cause timing to be off as much as degreesProper timing is critical and this situation could contribute to spark plug foulingUse calipers (shown below) and measure from one side of the crank position sensor housing to the magnet, then measure from the other side of the housing to the magnetIf the magnet is off-center by more than 0.254 mm (.010 in replace the sensorEngines above serial number 0T482780 have sensors that were inspected at the factory and do not require further inspection