Fuel pressure regulator spikes?

[Masonmobilemarine]

2004 f115txrc

Running issue. Give it throttle and it tops out at 3,000-4000rpm (varies) and can't get on plane.

On trailer it idles fine, but soon as you give it the slightest throttle it bogs or dies.


Check fuel pressure and it's fine at key on and idle is good at 36. WOT spec is 44.

When I give it throttle, even very slowly...from about 700 then to 900-1000, it will bog and the fuel goes to 44-48ish. Sometimes it goes to 50+ and dies.

It is normal for pressure regulators to spike like that, especially when throttling up so slowly?


Compression is good, did drop test on cylinders (injector and spark) and good there.

[fairdeal]

that doesn't seem right;
my understanding,
the 'default' setting of the regulator should limit rail pressure to ~44 psi
and then when manifold vacuum acts on the regulator, it further reduces pressure to 36 psi

so I would interpret seeing > 44psi as a "sticking" regulator

would 50 psi rail pressure at near idle result in 'flooding' and cause the engine to stall? IDK


then theres the no power / no rpms under load - have you measured the rail pressure then?

[boscoe99]

Different motors use different injectors and different fuel pressure regulators that have different fuel pressures.

The pressure regulator is plumbed to the intake manifold. With the motor off and the fuel pump running, the fuel pressure will be as high as it can be. The manifold pressure is as high as it can be. Reference fuel pressure is 43.5 psi.

Where in the book are you seeing the fuel pressure should be 44 psi at wide open throttle? That does not seem right.

As the manifold pressure lowers (motor being started and idled) the fuel pressure will drop. Should hold steady.

As the throttle is opened the manifold pressure increases. Since the regulator is sensing manifold pressure, as the manifold pressure rises the fuel pressure should rise accordingly. And hold steady if the manifold pressure remains steady.

If you are seeing a fuel pressure that is higher than that seen at key on with the motor off, that would lead me to believe that the regulation is kaput.

[boscoe99]