Help, Mercury 2011 4.3 MPI starts great then stalls

Ynot4me2

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Hi all, I really hope some can help. Here's what I have, 2011 Four Winns H200 with a Mercury 4.3 MPI with only 160hrs. Maintained annually and winter stored in heated garage. I'm the original owner.
We live on a fairly big lake and last weekend we went for a ride. We had our grand daughter (18 month) with us for the first time. We decided to beach for an hour so she could play in the water. Of course, this is at the other end of the lake. Got back in the boat and every time I tried to start it would stall. I never had any issues with this boat. It would start great then immediately start to loose RPM and stall. I did this several times and same result. No alarms. We were lucky enough that a guy that was beached also lived in our bay and gave a tow. During the 45 min tow, I kept trying to start it (lost count how many times) same thing. Starts, then loses RPM, then stalls. Had half a tank of recent gas, even switch over to other battery. Check all oil levels, the gear drive levels were just above the add line. Top it off. Still no go. After docking, decided to give it one last try and it started. Gave it some throttle in neutral and all good. The next day, I charge up the batteries, and top off the fuel (thinking maybe my gas gauge was defective), nope it took half a tank. Decided to start it, and it started and ran great. I didn't have time to take it out. Now I'm scared to take it out and be stuck again.
Sorry for all the babbling, just want to paint the story and give as much details.
What can it be? It was a warm and sunny day but nothing out of the ordinary.
 

alldodge

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Howdy
What is the motor serial number?

When the key was turned to ON before start did it beep?
 

Ynot4me2

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S/N is 1A643246
Yes, there was always a beep every time I turned the key as it did since day 1. This is normal, right?
 

alldodge

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Yes that is normal, unsure if your motor does a 1 or 2 beep each time, but this is the PCM checking things and saying its good to start.

Its going to need to do it again to find the issue

It would start great then immediately start to loose RPM and stall.

This comment leads me to the fuel pump is not staying turned ON. The pump turns ON when key is turned, but when it starts the pump may not turn back ON. If this is the case then it could be the relay or the connections to the relay or pump
 

Ynot4me2

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So, someone asked me, as I was talking about me problem, if I've change the water/fuel separator. This boat has been dealer maintained yearly before storing for the winter so I presume so. Looking on the web, do I even have a fuel water separator and if so where would it be?
Another thing that I read here on this forum, is the oil pressure switch and the IAC. Could any of these be the problem?
 

alldodge

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Your fuel filter is on the starboard side just below the drive lube bottle, but don't think that is the issue

https://www.mercruiserparts.com/bam/subassembly/31503/13808/70

If you can put the throttle handle in throttle only mode, giving it a slight bit more gas and the motor will stay riunning until its brought back to normal idle, then that would be the IAC
 
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