Bad Bird

I have a pair of 525's in a 35' Formula (05). Three weeks ago the Port engine started backfiring and shutting down above 3500 RPM. Took it in for repair and mechanic said there were two error codes in the ECM....faulty cam position sensor and faulty crank shaft sensor. He replaced the cam position sensor and checked the codes again and they were all cleared. Next trip out the boat ran fine. Last weekend the same problem started occurring again. Replaced the crank shaft position sensor this time, but it did not cure the issues. Funny part is, if I keep the RPM's below 3000 on the port engine it does not occur, above 3000 RPM, it takes a few miles down the lake and it starts acting up and shutting down with no audible alarm going off.

Any thoughts would be appreciated.....ECM issue maybe, fuel pump?

Sydwayz

How old is your fuel? Was it stabilized if its been in the tank a while? Ethanol fuel?
I'd look at a fueling problem.

Raylar

Many times on the newer Merc engines using the PCM555 such as the one on this engine, when the engine stalls or shuts down without warning the ECM will record cam position and crank sensor code faults when there is nothing wrong with either sensor.
I suspect unless there are other codes that your problem is fuel related as Sydwaz has posted, or you could have an intermittant electrical interruption on the engine and harness connections.
Service all your fuel filters and seperators , make sure all the fuel pumps are pumping and measure fuel pressure under load-underway and verify if there is a pressure drop under load.
You can move the harness and connections while underway and see if the engine shuts of or stumbles.

Best Regards,
Ray @ Raylar

MER Performance

Ray, I totally agree with you, bad electrical connections. Fuel pressure, yes for sure. I have seen service done on filters and not fill filter with clean fuel, then start engine and damage fuel pump. His service person should have water tested with fuel pressure gauge and scan to complete troubleshooting.

MER Performance

Wow! I have 308 post, I better get back to work or I'll be on here to much. People will think someone is paying me to be here.

EdNewman

Check your mechanical fuel pump. If it has leaked gasoline into the pump body and worn down the arm enough, it could be starving the engine of fuel.

Bad Bird

OK, problem moved from the port side engine to the starboard engine this weekend. Definitely an issue that is common to both engines. I'm leaning towards fuel related problem.
Interesting, maybe related issue. I have had fuel dumping out of my external vent line this summer (twice) after filling the boat and leaving it in my metal storage building..... (100 degree days). After finding it I removed the gas cap and heard the woosh of pressure being released from the fuel system.
I have a feeling I may have a blocked or filled vent line causing a vacuum on the fuel system and shutting down either engine at times.
Any opinions and remedy suggestions would be appreciated.

Bad Bird

OK got frustrated Friday night and pulled off the access plate to the gas tank just started removing hoses.

No problem with the vent lines
Pulled the sending unit assembly apart and looked down in to the tank.......BINGO! Found a small round seal that goes inside of a cap to seal the lid. Must have come off of the bottle of fuel additive that I use and was getting sucked up on the pick up tubes at the bottom of the tank. Fished it out and the boat ran great on Saturday.

Note to self....pay attention when pouring fuel additive into the tank.