Drop from cruise speed to 2000 rpm instantly in low hour Mercruiser 350 Mag MPI

[Desert 2 Sea Dad]

Good day all! I am looking for help. I have three mechanics and one surveyor trying to figure this out, but still no luck. I have a 2000 310 Sundancer with twin Merc Mag MPIs with V-drives. Only 50 hours on 2018 rebuilds. I was cruising at 3600 rpm when suddenly, the port engine lost power and dropped to 2000 rpm. No alarms, no strange sounds, temp good, oil pressure good, all good - except I couldn't get the port engine past 2000 rpm. After trying several different things (restarts, shifter and throttle movements) still not luck. I limped her back to the slip and began looking for answers. The mechanics ruled out these possible causes: Bad fuel, water in fuel, clogged fuel lines, bad fuel injectors.

Both fuel pumps were pressure tested and the readings were on the low side (low 30s psi I was told). Not clear as to whether or not fuel pumps might be the issue - but I am very hesitant to spend big $$$ on new fuel pumps on a hunch. Could it be in guardian mode? Anyway - why would only one engine be affected if both fuel pumps were showing reduced pressure. The starboard engine is fine. ANY IDEAS WILL BE GREATLY APPRECIATED!! Thank you!

 

[Woody]

I had the same thing happen on my 280DA with twin 5.0. I had the smartcraft stuff on my boat. On one engine the oil pressure switch failed. This is not the regular oil pressure sending unit. On my 5.0's they were right next to each other, you could put your hand on both at the same time. I don't know if you'd have the same on a 2000 year boat.

 

[Desert 2 Sea Dad]

I think my boat is too old to have the Smartcraft system. Could be an oil pressure sending unit though. I will find out more later this weekend. Very frustrating.

 

[cfd95]

I would check ignition
Bad coil?
Starts to fail when it heats up.