i have about 50000 on my 05 4.7l and about 20000 i check it and it was dead nuts on. I haven't checked it in awhile (had other problems)

 

I took a look at the FSM and the "Fuel Pump Module" includes a suction filter, pump, pressure regulator and discharge filter. With that, it may look like a "returnless" system on other new vehicles since it doesn't have a pressure regulator and return line on the fuel delivery manifold under the hood but it's not the same.It doesn't appear to use a PWM control to regulate pressure by varying pump speed like those newer systems so I believe it just uses the relaying to start the pump and the pressure regulator maintains the system pressure. If that's true then the pressure should stay fairly constant unless the pump wears to the point it's discharge pressure is less than the regulator setting, or unless the regulator setting drifts. The only other variable is whether the fuel pressure regulator is before or after the discharge filter. If it's after the discharge filter it would compensate for filter pluggage but if it's before the filter, the regulator would maintain constant pressure up to the filter but the actual supply to the engine would be reduced as the filter plugged over time. I can't really tell how it's arranged from the picture in the FSM but someone who's had one out may know.

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