Bad batteries/alternator cause crappy running?

[masongardner]

I'm still trying to track down why my boat is acting up. 2005 24v marine power 5.7. Had a bad episode where it died, thought it had run out of fuel. Towed it to the marina, filled it up. Didn't take a whole tank so we know it wasn't empty. Took it home, pulled the fuel filter dumped and water out of it. Dumped a can of seafoam in it in case the problem was water in the fuel. Brought it back today, drove probably a mile to the marina, 20 mins or so, was fine. Let in sit in the slip running and once in a while, say every 5 mins or so, and get real choppy and bad idle. I can rev it in neutral and save it. It sucking a ton of air when it's trying to catch itself. My thought are low pressure fuel pump (I can change it in the water right? When it tried to catch itself and is running rough, the volt gauge is all over the place. I'm assuming from the barely idle.

[lee]

The wire could have slid of the low pressure pump.

[masongardner]

Checked em, they are good.

[masongardner]

well, pulled and tested my batteries, which are good, since my boat is in a slip a couple hours away i didnt get the alternator tested, but figured if my batteries are good then my alternator is ok. I also replaced my low pressure pump and fuel filter,still not running right this sucks!! My boat sounds like it has an awesome cam in it with the idle.

[lancehon]

Mine did the same thing, it was a vapor lock issue for me, everytime it sits and idles after its warm it runs really rough. If I shut it off it won't start till it cools down. Ended up being winter fuel laced with ethanol. I drained the entire tank and refilled with new fuel

[masongardner]

That makes me feel a little better. The marina is pumping out the tank on monday or tuesday, re filling with non ethanol fuel and stabilizing.

Did it end up helping the vapor lock issue? I'm trying to think when mine is doing it, I think it has been after slow idiling each time. I always had the perception that vapor lock was the hard to start after running hard idea.

[lancehon]

I haven't tested completely but I did find that when I put my old gas in an older truck with a clear fuel filter by the carb after a few minutes after shutting the truck off the gas was actually boiling in the filter. Looked like water boiling in a pot

[masongardner]

Holy crap! Sounds like you made the right decision pulling that fuel from the boat!

[lancehon]

It was good to actually see what it was doing in my fuel system, glad it's out of there

[masongardner]

Well, the marina checked my fuel and its fine. I replaced the low pressure pump and the fuel filter. Still no go! The marina checked fuel pressure at the rail and it would drop off every couple minutes or so. My summer is slowly disappearing with a broken boat.