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2012 Mercury 40 hp EFI 3 Cylinder Cam Sensor Fault

D

dbieganski

New member
Hello, I have a 2012 40 HP EFI 3 cylinder four stroke that is giving me some grief. It started stalling at the end of last season while on plane. It would start back up and miss a little bit then recover. When it stalled it would give one long beep. I purchased a Rinda Tech Mate and all of the appropriate cables to read the fault codes. I found a Cam/Crank sensor error (M77) in the fault history. I purchased and installed a new crank sensor (the one that reads the teeth on the flywheel) as well as a new timing belt. Yesterday on another test run. I received the same fault and symptoms (M77). The flywheel is in perfect condition as everything else under the hood. I installed new plugs and replaced the fuel line and pump ball from the tank to the engine. I replaced the fuel filter and blew out the fuel line to the filter. Any assistance would be much appreciated.

Thanks,

Dave
 
kavie said:
Check the belt tension, should not be more than 1/2" deflection. I hope you get it resolved, good luck.
Click to expand...

Thanks for the information. I believe that the new belt is within spec but I am not sure how much pressure is required to check the deflection.
 
dbieganski said:
Thanks for the information. I believe that the new belt is within spec but I am not sure how much pressure is required to check the deflection.
Click to expand...

I believe that I found my issue. For future reference I found that one of the cam sensor wires was chaffed and contacting the hood mount in the front of the engine. There was another (purple wire) that was also chaffed and contacting the same hood mount. I believe that this was causing continuity between these circuits. All of this is in the bundle that feeds the PCM.

I applied silicone the bare spots and wrapped the bundle in a rubber sheath. I'll test drive this weekend.

Thanks,

Dave
 
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