Chasing a gremlin 350mpi

[cappie]

I have been trying to figure out this problem for a while. Its my starboard motor 300hp mpi OLO676540. the boat is a 2002 28 albemarle with straight inboards. Bought the boat 2 years ago. Put a new long block in due to oil pressure loss. However the old motor had the same problem.

Problem, Occasionally I bring the boat up on plane and the RPM's drop and the motor makes loud valve train tapping noises. So I come off plane, listen,(always sounds fine) and start back up gain. Some times it takes a few shots but it usually clears up. The other issue is, on start up, the same motor runs really rich but again clears up after it warms up. I'm worried that it is leaning out and the computer is dumping fuel in to cool it off.

What have I done. Merc scan tool shows no stored codes. Had my marina hook up the lap top while running and of course everything was functioning as it should.
Plugs had bad carbon build up from running so rich.
-Full tune up including plugs, wires, cap and rotor.
-Changed entire fuel cooler, regulator and pump system with the new motor.
- Coolant temp sensor and iac sensor.
-Cleaned flame arrestor and throttle body with pro-tune.
-New fuel lines from tank to separator, and the 2 lines from sep to pump and regulator

At this point I am ready to swap the ECM with the port motor or start looking into injectors. I have never heard of an injector going bad but I am leading towards an injection problem?
Any ideas would be greatly appreciated
Erik

 

[Don S]

Re: Chasing a gremlin 350mpi

Have you checked the oil level? Before you start laughing, if the oil level is over full it could be the cause of your problem.
With a high oil level, especially on a straight inboard, the crankshaft may be hitting the oil. When this happens, it aerates the oil which in turn causes the lifters to get soft and the rockers start clattering and the valves don't open as much. Since the valves don't open all the way you aren't getting enough air, but the fuel system is still putting in the same amount of gas (runs rich)
This will also show low oil pressure on your gauge.

Since you have two engines, make sure the dip sticks are the same and the dipstick tubes are in the same places.
Have you notices the bad engine taking more oil for an oil change than the good engine?

 

[cappie]

Re: Chasing a gremlin 350mpi

It hasn't been taking more oil but I will check into what you said. I hope it is that simple.
Thanks
Erik