t/225 TXR 2006 fuel pressure drops at rail

[Phillyc1]

Have a pair of 225 TXR's 4 stroke fuel injected. Port Engine has a new LP pump, fuel is getting to the VST. Put a pressure gauge on the high pressure side. Turn the key and 40PSI. Starts and idles at 40PSI. (LP pump runs 10 secs on, 20 sec off). Throttle up 2300RPM's and holds 40psi for 30 sec to a minute, then pressure drops to 20psi, engine dies.

Screen on HP pump is clean. rubber grommet that the HP pump goes into is tight.

Where do I go next?

1. Fuel pressure regulator - looks like a relief valve on top of fuel rail?
2. read that their is a check valve on the high pressure fuel line between the rails, could be clogged. had problems with the white junk in VST clogging screen previously.
3. Could check the needle. had it stuck once before, but unlikely. I turn key again after it stalled and back to 40psi.

[fairdeal]

a puzzle

1. Difficult to imagine a simple pressure regulator acting like that.

2. There is no check valve on the fuel rail - there are a couple "disconnect fittings".
I suppose it could "corrode" - restricting flow ? that seems farfetched also

3. I want to think you are just running out of fuel in the VST
but "turn key again after it stalled and back to 40psi"

strange

[boscoe99]

Something seems to be amiss with the pressure regulator.

The pressure regulator is plumbed to and correlates with the intake manifold pressure.

With the engine off and the key on, the fuel pressure is as high as it will ever be. Why? Because the intake manifold pressure is as high as it can ever be when the motor is not running.

Start the motor and the intake manifold pressure will drop. So too should the fuel pressure.

The service manual says that the fuel pressure should be 44 psi when the key is just turned on. The SM says that the fuel pressure should be 38 psi when the motor is idling. Stands to reason. When the motor is started the intake manifold pressure drops by about 7 psi. So too should the fuel pressure drop by about 7 psi.

If you have twins, why not swap the pressure regulators over from one motor to the other and see what happens.

[Phillyc1]

Boscoe

Thanks for the suggestion. I will switch the pressure regulators and see what I get. Hopefully there is a reusable o-ring or seal for the regulator.

I get that the pressure in the intake correlates to pressure in the regulator. How does the regulator work? I thought it worked like a pressure relief valve, ie... pressure in the rail exceeds Xpsi and the valve opens to release excess fuel pressure.

In this case, it is not. A leaking regulator is bleeding fuel pressure in the intake manifold, correct?

[fairdeal]

early 2000s F225 fuel rail pressure regulator

[rodbolt17]

you have a VST issue.
could the regulator fail?
yep.
but I have never seen a 4 stroke Yamaha regulator fail and that goes back a few years.
I have seen a few rust away but not fail.
the only reason they attach it to the manifold pressure is to aid in rapid acceleration.
from 13 or so "Hg to almost baro it can alter the PSI about 5-8 PSI.

at idle with the shutters closed you have a "vacuum" or a reduced manifold pressure.
at WOT you have little vacuum and intake air pressure is almost barometric pressure.
if you wish to test it simply unplug the vacuum line and run it.
odds are you wont see much difference.