The number one answer to this question is usually is "VATS", is it wired up with the BCM and Key, is it disabled or do you have a VATS Bypass/simulator?
other would be to check the battery 12v's as GenIIIDude suggested, also check the grounds, fuel pressure and voltage to the relay.
71' Chevelle, 99 LS1/Viper T56,Full Hotchkis TVS,Custom Cowl Induction CAI
84' Z-28 350/T5 71' Nova - LS1/4L60E
, Full Hotchkis TVS Suspension
79' G-30 SWB 4X4 Van, 400cid / TH350 NP205
48' Ford F-1 1/2 Ton Truck, Stock 6cyc/3sp