With the engine running, pull the vacuum line off of the fuel pressure regulator.
It should pick up to 40 psi or so.
If not, probably new fuel pump time, or maybe time for a new fuel filter. Or a new fuel pump relay.
Maybe all three.
2007 Grand Marquis LS: 5.4 swap, 9.9:1 compression ratio, Comp XE268s, NPI pistons, PI heads ported by me, Accufab upper plenum, 75mm DBW throttle body, Factory PI intake with Chinese spacers, CVPI dual exhaust, CVPI torque converter, CVPI air-box and zip tube, J-Mod, 3.55 gears, FMS Trac-Loc differential
17" Dorman CVPI steelies, BFG Comp T/A 255/45 R17s