Vapor lock solution in F225 03

[Doggydog]

I see. So the speculation here is that LP fuel pump pressure relief valve may not be opening when it should. As in it may be requiring more than 10PSI before the valve allows fuel through?

and/ or the VST pressure relief valve, which should also open at 10PSI, may not be opening and the pressure I. The VST doesn’t allow for fuel to enter?

thanks for the video reference. That helps a lot. Do you mind telling me how that gauge test demonstration is setup? I’ll need to go buy a gauge and small compressor I’m guessing..

[fairdeal]

There are two very different problems possible with the Pressure Relief Valve -

1. corrosion makes it 'stick open' - it doesn't allow any pressure to build -
so then instead of keeping the VST full, the LP pump 'chases its tail' -
the fuel just goes around and around and the VST runs empty

2. corrosion plugs up the valve, there is no pressure relief. The LP pump blows fuses,
or it overwhelms the VST needle valve, fuel overflows out the VST vent and into the airbox,
flooding the engine.

As for the VST vent "orifice" gizmo -
I may have heard of issues where the vent was 'plugged'
and since no air could escape the VST,
the Lift pump wasn't able to get fuel into the VST.
But that doesn't seem plausible to me, at the moment -
and I don't remember clearly -
maybe its an imaginary (fake) problem.

[fairdeal]

You don't need an air compressor, a bicycle pump is enough.
Its always good to have a pressure gauge around

[Doggydog]

Okay. I’ll get some tubing and a gauge and test them out.

tips for getting them off the fuel lines without messing the lines up?

[marchmadness]

They should pull off with a little force. I have used wd-40 to help loosen the seal. If you still have the original pressure relief valve I would try to test it but I would look at that as maintenance and just replace it. Its $130.

[Doggydog]

I was finally able to replace pressure relief valve that comes off the fuel pump (69J-24460-00-00) yesterday. Hopefully that does the trick. The only other thing I’m considering doing is replacing the primer bulb in the fuel line. It doesn’t seem to act the same as ones I’ve used in the past. Hopefully that fixes the problems! If not, I’ll be back!

[fairdeal]

I'm considering doing is replacing the primer bulb in the fuel line.

I'm generally highly skeptical of blaming primer bulbs for engine running problems.

IMO, probably 99.9% of primer bulbs that are replaced
were perfectly useable - and not causing any trouble.

[Doggydog]

Sad to report that my motor stalled at *****ing speed (7k rpm or so) twice today. Appears the valve change did not solve my problem.

on the primer bulb note- when I do prime the bulb after a stall I’m always priming a completely empty bulb. Any ideas on that?

[Keithbaja]

Try a portable tank and sea what happens.. hooked up straight motor,,, also clear/remove the SS ball inside the anti siphon outlet valve on top of fuel cell...do NOT use screw hose clamps anywhere in the fuel system. Only Outlet single ear clamps should be used. OUT

[Keithbaja]

Oetiker hose clamp.. DN spell checker.. Grrr !

[Doggydog]

Alright - new season - same problem. Hoping you all may be willing to help me continue trouble shooting.

Bottom line - 04 F225 TXRC is stalling at idle and at idle speeds. The engine does not stall when underway. I've checked all filters, fuel lines, the bulb, etc..

After stalling the VST is in fact empty. To restart I prime the bulb and the engine runs fine for a while. Problem then repeats (more frequently this season).

I've replaced 69J-24460-00-00, the pressure relief valve. I also paid a Yamaha spe******t in the area to T off and vent the line going from the VST to the atmosphere and inspect the fuel system. I assume that takes part 69J-14989-00-00 out of my troubleshooting equation.

I'm thinking my next step is to replace the low pressure pump in hopes that is simply not keeping the VST full at idle and low speeds. Does seem like the most logical step?

[Keithbaja]

OMG !! Have U tried using test tank hooked straight to motor ?? Yes or no

[fairdeal]

I'm thinking my next step is to replace the low pressure pump in hopes that is simply not keeping the VST full at idle and low speeds. Does seem like the most logical step?

No, not logical, but rather magical thinking.
If the lift pump is capable of keeping the VST full when the fuel demand is high,
it is capable at minimal demand;
the pump is fine.

There is a distinct difference however
in the pump's behavior at <1200 rpm vs >1200 rpm
Below 1200 the ECM only runs the pump part -time
(I've forgotten exactly, 10 seconds on, 20 off?)

I would be looking at the fuel plumbing between the tank and lift pump -
for, perhaps, an air leak
that allows fuel to flow back to the tank when the pump is off
and makes it 'lose time getting started' when powered back on.

Or as Keith suggests,
temporarily replace the fuel supply to the lift pump
and see if the problem goes away -

[Doggydog]

I have inspected all the lines. I didn’t see any leaks. But I’m guessing this type of leak would be a very minor slit in a line that would barely be noticeable.

To be clear, you’re saying every line starting at the fuel tank and ending at the low pressure pump intake. Right?

I have not used an external tank. Maybe I can find one to test with though if that’s the only smart thing to do at this point. What part of the system would the external tank be connecting to? As in which part of the plumbing would I disconnect and connect to a tank?

As always, thanks for the help. This is becoming a frustrating dilemma. (Boat is at a boatel so I only get to test one thing every week or two…)

[99yam40]

I would go for the primer bulb area or the fuel pumps area.
you cannot see a vacuum leak that sucks air in.
gaskets on filters and all screwed in fittings and leak as well

I have read that a clear piece of hose right before or after the pump could show bubbles if there was air being sucked in lower than them