Hi there, that serial number is coming up as an H.O.... MERCRUISER 496 MAG HIGH OUTPUT 496 HO BRAVO MPI model number 4T42028N1
https://www.perfprotech.com/mercury-...g/umodel/28609
The PCM will only record engine hours while the engine is actually running...Not by leaving the key on.
If someone will re-scan the PCM, there is a section they can go into and read the RPM history. It will tell you how long the engine has idled, plus been ran between various steps throughout the rpm range all the way to wide open throttle. If you're seeing two different numbers, then something must of been overlooked.
^ Oh I forgot to mention that within the scan tool features there is a section that someone can erase the run RPM History but the total hours will remain the same unless the ECM was sent in for repairs somewhere then the total hours have been known to go back to 0.
Someone may have erased them at one point so that would be why you're only adding up 61.8 hours.