Starving for fuel
 

When I run my boat at around 55 mph for around 10-15 minutes straight the port motor will start to lose fuel pressure and eventually die out. If I let it sit for about 10 minutes the motor will start right back up and run ok for a while until the fuel pump gets "hot" and then it will start to act up again. I already changed the fuel pump on the front of the motor. I have not changed the fuel pump on the back left side of the motor yet and I am wondering if anyone has ever heard of this problem before..?

Motors are 2003 Mercury 496 Mag H.O.

Any help would be greatly appreciated.

What about fuel filters? Might not be able to keep up if they are dirty.

brand new fuel filter spin on and I also cleaned out the filter element on the back of the motor along with the screen on the first fuel pump

Collapsed fuel line from tank to filter? Obstruction in ball valve? Sticking check valve? Do the tank pickup tubes have the screen mesh filters to prefilter the fuel? Just a few random thoughts
Could rig up a way to swap fuel feeds between motors right before going into the fuel sep and see if problem goes away or swaps motors. I'd do that without doing anything else (ie: blowing out lines)so as to make sure the problem can be narrowed down to just 1 change at a time. Nothing like doing several things at once and not knowing what the problem was.

Possible tank venting issue, obstructed/plugged vent ?

its like a wild goose chase...I wish someone has had the same problem

I'm with Kelly O. Easy enough to troubleshoot. Go unscrew your gas cap a few turns next time out and run it. See if it does it then. It sounds to me that the longer you run it the bigger a vacuum you create until it finally won't allow the motor to draw fuel. At that point it stalls, wait a few minutes and your clogged vent or another leak equalizes pressure and you're good to go again.

Symptoms with several possibilities. Best to just start eliminating them 1 at a time.

Ok I went out and performed this test and it didn't make a difference...

When I run the boat at around 3500-4000 rpm for more than around 5 minutes straight the port motor will start to stutter and drop rpm but it will catch itself on and off for a while until it will finally die out. I am running the boat with a fuel pressure gauge and I am keeping the engine hatch popped open a little to watch the gauge. The fuel pressure is dropping off then back up then dropping off until it will finally die. It takes a while for it to actually die out maybe another 5-8 minutes.

I already changed the fuel pump on the front of the motor...I am now leaning towards changing the one on the left side of the motor next.

when we were out testing we saw some pretty good numbers on the GPS.....75.1 MPH with full tanks of gas and 2 of us in the boat. I thought that was pretty good for twin 496 MAG HO motors...saw the fastest speeds just before the motor started to die out...hahaha