The fuel pressure regulator could very well be sending the fuel back to the tank before the proper pressure is developed, or the fuel pump itself could be bad.
The fuel injection system on this vehicle requires a very specific pressure to open the injectors, and you will need to attach a fuel pressure gauge to determine what the exact pressure is. Just because you can tell there is fuel in the lines doesnt mean that the pressure is high enough.
Get a gauge and test the pressure.
The diagnostic pressure valve (Schrader valve) is located on the fuel supply manifold (rail). This valve provides a convenient point for service personnel to monitor fuel pressure, release the system pressure prior to maintenance, and to bleed out air which may become trapped in the system during pressure replacement. A pressure gauge with an adapter is required to perform pressure tests.
Fig. 4: Fuel pressure can be checked using an inexpensive pressure/vacuum gauge
If the pressure tap is not installed or an adapter is not available, use a T-fitting to install the pressure gauge between the fuel filter line and the throttle body fuel inlet or fuel rail.
To test the fuel pump, follow the accompanying diagnostic charts. Testing fuel pressure requires the use of a special pressure gauge (Ford Tool T20L-3314-B, Rotunda Fuel Pressure Testing Kit 014-00441, or equivalent) that attaches to the diagnostic pressure tap fitting. To perform the fuel system test a scan tool is necessary to access the different test modes.
Depressurize the fuel system before disconnecting any lines.
If you have further questions on this, please feel free to reply.
Thanks for asking!