F115 won't rev past 4,000 WOT

[fairdeal]

Fuel pressure holds solid at 40psi at 4,000, runs smooth. as I move lever forward, fuel pressure starts to drop and it starts to bog. If I romp it at lower rpms, it bogs and will drop to about 20 psi, even if running only 3,000.

you need to find out why the rail pressure is dropping.

^^^^

The high pressure "system" - HP pump &pressure regulator -
is 'standalone" -
the pump is simply constantly 'on'
the regulator acts only on intake manifold vacuum.

Nothing the ECU does, or the TPS setting,
can change the rail pressure.

The most likely cause of the rail pressure dropping to 20 psi
is the VST running low/empty.

[fourvalv]

Update: VST had a very high amount of what appeared to be a rust sludge. Looks like it was coming from outer housing of the HP fuel pump, which was fairly rusty. Even though the VST was 'new', the boat wasn't used for a while, so the moisture got to it. VST screen was the obvious answer from start, but made assumption it had to be fine since it had been totally replaced. Just sat too long I suppose. Actually the 'screen' wasn't too bad, but guess when at higher throttle it was sucking the rust up off the bottom to block the screen.

Boat now runs fine, pulling 5800, smoothly with no surge or drops. At least for the time being.

As extra precaution, have pulled, emptied and cleaned fuel tank, flushed new fuel through lines before attachment, etc. Also will use a fuel treatment that states it offers some rust prevention going forward. And hopefully use the boat a lot more.....

Thanks for all help.

[TownsendsFJR1300]

Just a note re the above...

On my F150, after several outings, I'll drain the VST and catch what comes out in a clean tuna fish can. (Just one screw after removing the hood).

Gives me an idea on what's going on in the VST/fuel and doesn't take long... If some debris, squeeze the primer and flush it...
At least some of your rusty crap likely would have came out pointing to your rusty, internals of the VST.


BTW, I'm still on the original VST filter (2006 engine), VST was pulled apart once under warranty-
(low idle issue)


Non-E fuel, if possible, is well worth the extra $ (IMO) in the long run...


.

[99yam40]

Update: VST had a very high amount of what appeared to be a rust sludge. Looks like it was coming from outer housing of the HP fuel pump, which was fairly rusty. Even though the VST was 'new', the boat wasn't used for a while, so the moisture got to it. VST screen was the obvious answer from start, but made assumption it had to be fine since it had been totally replaced. Just sat too long I suppose. Actually the 'screen' wasn't too bad, but guess when at higher throttle it was sucking the rust up off the bottom to block the screen.

Boat now runs fine, pulling 5800, smoothly with no surge or drops. At least for the time being.

As extra precaution, have pulled, emptied and cleaned fuel tank, flushed new fuel through lines before attachment, etc. Also will use a fuel treatment that states it offers some rust prevention going forward. And hopefully use the boat a lot more.....

Thanks for all help.

you have to wonder how moisture got in there to rust things up.
e fuel possibly and I would worry about what it did to the inside of that pump motor too since the fuel runs thru it to lube and cool it when running

[oldmako69]

Clogging of the VST by particulates seems to be quite common. The assumption that "it had just been cleaned" I feel is bogus. I had to clean my VST screen TWICE in ten hours of operation. The engine would not rev above 3900. The screen was mechanically blocked with fuel line detritus. You do not need to replace the $40 VST screen. Carb cleaner does the trick quite nicely.

As far as moisture, I think people are confused about Ethanol, or perhaps I am. No water evident in the Racor strainer bowl does not mean that there is no moisture in the fuel. Ethanol is hydroscopic and as such, it absorbs water. From the air on top of the fuel, which takes on moisture from the fuel vent. I think this is why fuel pumps are rusting. The HP pumps can show corrosion on their outer surface as well as their interior workings which pass the fuel on.

There have been multiple threads online about guys finding rust on that VST screen and fouled injectors.

What's needed is a small inline fuel filter in the line FROM the injectors. One easily accessed and serviced. One with a SIGHT GLASS would-be killer, but it would have to be able to handle the fuel PSI. Till then, get used to pulling your VST.