2005 F250 losing prime

[99yam40]

what do you not understand about it sucking air instead of fuel?

you have a leak , find it

[Kimsboat]

I understand an air leak........On the forum looking for possibilities.......

[Kimsboat]

Good Idea-Thanks.... give it a whack and let you know.

[FabricGATOR]

How about full tank vs half tank. I was drinking a Coke the other day and my straw had a crack in it. It worked fine until I got half way done, then I started sucking air... I was as frustrated with my situation as you may be with yours!

[marchmadness]

I started my own post because I'm still having the same fuel issue . Last year I replaced The pressure release valve , so of course almost a year later I had the same issue happened again yesterday The VST tank ran out of fuel the motor died , The Ball was soft I was able to refill the VST tank with the primer ball and restart the motor and it ran fine let me know what you find out and maybe we could help each other I will be working on mine tomorrow

[Kimsboat]

I caved in...

ADD TO THE LIST OF REPLACEMENT PARTS

pickup tube in the tank , elbow and ASV. Yamaha **** plated primer bulb, 3/8 hose from the tank to the engine, hose clamps and ......the low pressure fuel pump.

So all in all i have thrown the kitchen sink at it. I plan on running tomorrow.

[Kimsboat]

Yes.

I called the tank manufacture and they walked me thru the test procedure. Pick up tube tested perfect.

[99yam40]

did you look at the filter seals and connections also.
only so many connections between tank and pump where you saw the bubbles

[Kimsboat]

Ran 120 miles yesterday with no issues!

Before I left in the morning I changed the spin on yamaha filter on that motor. Other filter was only a couple of weeks old.

I quess that was it. Thanks for all the help and 99yam40 thanks for reminding me to check that filter again.

[DaveF114]

I have been following many of these posts as I have had the same issue with a 2004 F225 that would idle fine while cold, run all day at speed, and then die after 5 minutes at idle. Pump the primer and good to idle for another 5-6 min. I could not find any leaks in the fuel system and pressurized it to be sure. It held 8psi indefinitely. I changed the low pressure pump, the relief valve attached to it, the primer ball, the anti-siphon and pickup tube. All new filters were in place. I did not do all this at once, but changed a few things at a time. No change in the problem.

To test things out, I added clear hose at the intake of the low pump and a second one prior to the Tee so I could tell if I was getting air coming from the on-board filter and/or the pressure relief valve. I also added a pressure gauge at the output of the low pump, and a second one before the "Orifice, Air Vent of the VST tank. When I attempted to test this, the temperature warning came on so I could not complete until after I changed the water pump... Change the water pump and now the engine runs fine... It only had the stall problem after it warmed up. Can there be a connection? Just worried this isn't over...

[rodbolt17]

have you tested fuel system vacuum.
not the first anti-siphon valve I ever saw with excessive head pressure setting.
'

[DaveF114]

I ran it with and without the Anti-Siphon valve to see if it made any difference. It still stalled at idle (after it was warmed up) with and without. Only difference I could see was that the primer ball was a little slower to re-fill when pumped with the Anti-Siphon valve in place indicating a little more of a restriction which I would expect.

[DaveF114]

Fished yesterday and as expected the problem is back. Ran fine at speed but dies at idle until you pump the primer ball... When running right, I could see clear fuel coming from the supply, but lots of bubbles coming from the relief valve side. Pressure was reading ~10-14psi. Started at 10 but looked to go to about 14 when the VST tank filled up. Pressure at the "Orifice Air Vent was 2-5 psi.

When it wasn't working right, you could see lots of air in the line and I suspect an air lock at the pump? Start squeezing the ball and it would pick it up and start pumping again until the auto shutoff at 10 seconds. When it started again, sometimes it would continue working, other times it took a couple of cycles...

This morning I checked the vacuum pressure coming from the tank which was about 2psi. I also tested the low pressure pumps (original and new). Original would not pull the fuel up a line more than 6 inches. New pump pulled fuel up 30 inches with no issue, but after testing for ~15-20 minutes, it began to fail to start... You could here it click internally, but would not run... Feels like original pump died of old age and I got a bad replacement?

[boscoe99]

If I had an EFI Yamaha with an electric fuel lift pump, at the first sign of a problem I would replace the Yamaha fuel delivery system to the VST with a Holley electric carburetor fuel pump (high volume, low pressure, maybe 4 psi) located near the fuel tank, or coupled with a Racor fuel filter. Many of the HPDI bass boys have done this to do away with the crappy Yamaha mechanical lift pumps. Seems to work and work well.

For some reason there is no problem with the Holley pump running continuously without fuel be recirculated as there may be with the Yamaha pump. A wire is run from the hp fuel pump to a relay at the Holley pump. The Holley pump runs continuously whenever the hp pump runs.

Yamaha has no objection to the use of electric fuel pumps with their carbureted models so there should be nil objection with the use of same to supply a VST.

[rodbolt17]

as long as the pump is USCG rated and it is wired in accordance with USCG regulations a pump is a pump is a pump.