350 Mag MPI Alpha 1 - IAC symptoms but I've already replaced IAC

rjhall01

Recruit
Joined
Jun 8, 2020
Messages
1
I re-powered in 2019 with a new crate 350 Mag MPI. Ran fine for 30-50 hours last season. On launch, got the 2 beep/minute soft alarm but boat ran fine with normal temp/oil pressure. Over time, began to experience low rpm/idle issues and the alarm has never stopped (still normal temp/oil). The boat will always start from cold but sometimes stall when going into neutral after a run. Once stalled, you need to throttle in neutral (and can smell some fuel in the exhaust) to get it started. It will also stall during the transition from neutral to low RPM as you initiate the hole shot. My shop has asked me to pull the boat off my lake and bring it in for diagnostics, but I'm dragging my feet. I swapped the IAC this past weekend but symptoms/2 beep alarm persist with no change. What are the other probable causes? Block pressure sensor (doubt this since it would not cause idle issues)? Shift interupter Switch? A short somewhere? Fuel pump or filter? I'm willing to throw another part in and hope I don't have to pull the boat. Getting by with the alarm and symptoms but it's annoying.

Boat is a 2004 Crownline 210LX w/ 350 Mag MPI alpha 1 drive.
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
43,320
If the motor in the boat is the same as it was in 2004 then you would have a 555 ECM.
I'm reading there is a constant alarm, is that correct?
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
If you have an ECU engine (in other words, any EFI or MPI engine), and you are trying to fix alarms that could have a number of different sources, without the diagnostic software, you're shooting in the dark. We could all be offering different suggestions, and one of us MIGHT be right, but you don't know which one. And just throwing new parts at the problem gets real expensive, real quick!

2 choices... Take the boat and get the engine scanned and find out what's going on, or buy the Diacom software (I consider the Code Scanners a waste of money, given that the software is only slight more, and gives you real time data)... If you use the software twice to fix a problem, it's paid for itself.

https://www.rinda.com/marine/diacommarine.htm

Chris........
 
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