The Mariah Owners Club - 2010 5.0mpi mercruiser ECM help!

Hey guys I need help. I have a 24' custom skiff with a 305 with 260hp at prop. It's a 2010 model with alpha 1 drive. Serial number on engine is 1a614049.
Model number; 4-m4122lu u

The problem I'm having is with my computer (I'm guessing). Motor will not stay running at the moment. When I do a diagnostic Check it shows like my computer is not hooked up while it is. I can get it to turn over but will not stay running. I tried 2 other computers that come off of mercruiser engines and neither one worked. Not only would my motor not even try to start I couldn't run diagnostics with the other computers.
Two months ago I sunk my boat. Motor was running when boat went down. As soon as I got my boat up I immediately brung it home and drained everything and filled block and intake with diesel. The guy I know who installed engine in my boat is a mercruiser specialist...
Anyhow he come over to my house and helped me get my motor back running. I changed my starter, alternator, fluids, filters, gimbal bearing, seal, plugs, and probably few other things I'm forgetting to mention. After that I pumped out my tank and was able to get motor back up and running. My motor has sealed relays so he told me I got lucky there and mentioned how I got lucky I didn't fry my computer.
He stated that if my motor runs funny to disconnect the wire on back of rpm guage or buy another one. It wasn't quite running perfectly so I changed all my guages and did another tune up after taking boat out for the first time since back running. it didn't get better and now won't run.
I was considering changing my intake and going with a 4 barrel carb. I would really like to get my fuel injection back working and fix the issue. I forgot to mention that I changed my wiring harness out also just to eliminate any issues. It was a used harness that worked and I got it off one of the engines that I also tried using computer from that my mercruiser guy had at his house.
If anyone has any ideas of something it could possibly be or anyone can help lead me to finding a place to fix computer I have or buy another computer that's not couple thousand. I would really appreciate it. I actually figured I could use just about any mercruiser computer that would hook up to my harness but I'm guessing I can't after trying two different computers. This guy's