Fuel Pump / Gas Tank / Fuel Pressure Problem

[Patrick]

I have an Indmar 335hp engine on my 2003 wakeboard boat. 3 years ago, it started cutting out when I push the throttle forward more. I would ease off try again and it would usually work. Sometimes I would stop and start the engine and it would go away. It used to only occur when the tank was low. It's been getting worse and worse as time has go on and now it occurs everytime and the engine even backfires and dies sometimes. I've heard of vapor lock, but that only occurs if it wouldn't start I've been told. It starts every time but just cuts out and slows down when I hit the throttle.
I've had 2 different mechanics work on this and end up changing the fuel filter and cleaning the fuel screens which would make it better for like a day at that point. Now it's in really bad shape and not sure what to do and don't want to keep throwing money at mechanics that put on a 1 day band aid. I've used a lot of gumout, sta-bil, fuel injection cleaners last year to keep the boat moving with slightly less symptoms, but now no luck. Any ideas?

[jzelt]

Get a fuel pressure gauge and monitor it during all the stages. (This should eliminate whether fuel delivery issue or electrical).

The pressure should stay ~60 PSI. Ours read 30 even after changing the fuel filter. It was doing the same things you describe.
Replaced the fuel pump because after the filter, it died trying to re-prime the fuel line. (straight power to the pump did nothing, new pump same wires caused it to run like it should).
Haven't been able to try it out under load yet to see if remedied.

[sydneyACE]

^^ What he said.

It sounds like the fuel pump is the culprit to me.
Sometimes when they fail, they don't quit working all-together, but they won't build-up the pressure required for Fuel-Injected engines to run under high-load conditions.

That's just a guess though, so I would definately reccomend hooking-up a fuel pressure gauge as "jzelt" suggested to make sure that's what's happening. If you have good fuel pressure even under acceleration, then you most-likely have an ignition (electrical) issue.

If you are losing fuel pressure there could be a few different possibilities for the culprit.
#1. The fuel filter. Obviously you said you already had this changed, but sometimes there is more than 1 fuel filter. So do a thorough check to be sure somebody hasn't put another one on there somewhere. (One time we were working on a guys boat, with fuel problems, and we changed the filter... no better... we looked closer, found another filter and changed that... no better... guess what... the (old) boat had 3 filters on it!)
#2. The fuel pump. Just MAKE SURE this is it before you change it. It's probably an expensive part, and is most-likely difficult to change.
#3. A plugged tank vent could cause similar issues. If no fresh-air can get into the gas tank, it will build-up a vacuum as you idle around then when you give it more throttle, the fuel-pump might not be able to build enough pressure to supply the engine. (This is probably not very likely but it's worth checking before you buy a new pump.