Any thought about MX 6.2 MPI HORIZON issue

I have a 33' Egg with (2) MX 6.2 MPI HORIZON and have been experiencing an undetectable issue for sometime now.

Starting about a year ago our port engine would start to lose power (fluctuating RPM), with a detection of a backfire in the engine room. This seem to only happen after running for about an hour (each time), leading me to think it was somehow heat related. Both engines seem to run in harmony from start up, warm up and for the first hour of cruising.

I have replaced all plugs, wires, filters (multiple times) flame arrestors, rotor in distributors. Further more thinking it was some sort of vapor lock in the fuel tank/line confirmed not the issue. Ran fuel out of tanks, adding complete fresh fuel. This I have done myself.

Enlisted the services of a reputable service company in Annapolis. 2 mechanics for 2 hours could not find an issue, scanned codes on engines and found nothing indicating to this issue. Had boat hauled, found crab trap line tangled around port shaft. Thinking that would solve problem put boat in water and tested. No problem found on trial run.

Here we are now two runs later and problem still persists.

Any thoughts.......???

Re: Any thought about MX 6.2 MPI HORIZON issue

Because you have 2 of the engines it's going to make it easier... First thing I would do is to swap the ECUs across... That will confirm or rule out them... Then I would start looking at sensors... TPS, MAP, ect...

Chris........

Re: Any thought about MX 6.2 MPI HORIZON issue

I can see where this would be a tough one to diagnose, there are a lot of possible causes. Have you confirmed that the fuel pressure is correct and steady when the problem occurs?