Volvo Penta 5.7 TBI still being a pain

[Berkley1]

So I am still having a problem with my VP5.7 TBI not running at peak RPM so far I have checked the fuel pressure high and low all good no ASV installed changed fuel filter fuel looks good fixed a loose MAPP sensor hose new gaskets on throttle body check plugs all looked pristine distributor no corrosion. hooked up my Tech scanner shows max RPM 2950 under load and fuel consumption at 10.91 GPH which seems high could it be the IAC MAPP sensor I get no error codes I'm getting anywhere between 10 to 14.5 max MPH could it be outdrive related?

Signed out of ideas

 

[dypcdiver]

Does your boat have the Fuel Vapor Separator tank at the rear of the engine.
A couple of years ago I had some bogging and problems with getting on the plane. Turned out that the alloy Internals had corroded and stopped the cooling water passing through. So very hot fuel was being supplied to the throttle body which was instantly turning to vapor instead of liquid fuel.
My boat is the VP 5.0 GI PWTR (TBI) and has not missed a beat since.

 

[Scott Danforth]

have you done a compression test? all cylinders near 150 psi?

 

[Lou C]

You replaced the anti siphon valve but did you check the tank pick up tube for a screen clogged with gunk? Some have a screen some don't.

 

[JasonDom]

You replaced the anti siphon valve but did you check the tank pick up tube for a screen clogged with gunk? Some have a screen some don't.

yeah, run the motor off a portable tank with its own fresh line to rule out venting or pickup screens.

 

[Berkley1]

Does your boat have the Fuel Vapor Separator tank at the rear of the engine.
A couple of years ago I had some bogging and problems with getting on the plane. Turned out that the alloy Internals had corroded and stopped the cooling water passing through. So very hot fuel was being supplied to the throttle body which was instantly turning to vapor instead of liquid fuel.
My boat is the VP 5.0 GI PWTR (TBI) and has not missed a beat since.

I do not Thanks though

 

[Berkley1]

You replaced the anti siphon valve but did you check the tank pick up tube for a screen clogged with gunk? Some have a screen some don't.

Yes pulled the tube completely clean

 

[Lou C]

keep at it you'll get it eventually!

 

[2009 stingray]

hey, check the fuel pressure at the throttle body. you want to see 30+ lbs with key on, engine off. if you have that, i have found that there is a set of filter screens inside the throttle body, sitting inside the injector bowls, the screen never gets serviced, buy this kit:

https://www.oreillyauto.com/detail/c/walker-products/walker-products-fuel-injector-repair-kit/wlk0/18023?q=18023

it has all you need to service the throttle body. although i am not certain on the fuel pressure diaphragm.

i had a boat this spring that kicked my butt and finally this was the problem, the screens were black and completely starving the injectors of fuel