i have a 1994 e150 4.9L. It recently started stumbling and missing very bad upon acceleration and even throughout all gears. i replaced fuel filter, made the egr restrictor plate. but i put a fuel pressure guage in the rail and i got only about 20 psi when you turned the key, if i tirn it on and off 3 or 4 times i can build it up to about 30 psi. when it starts it stayed at about 35 psi and when i shut it off the psi actually builds slowly to about 45 psi. is the fuel pressure regulator or the fuel pump bad and causing this lean/starving condition? thanks

 

Yes.

The Haynes manual tells how to diagnose them.