fuel injection help needed

I WILL TRY TO MAKE THIS AS BRIEF AS POSSIBLE.IM A VERY AVID 5.0 MECHANIC UNLESS IT INVOLVES THE ELECTRONICS.I HAVE CHANGED INTAKES ABOUT 15 TIMES ON EITHER MY TWO STANGS OR OTHERS CARS I HAVE WORKED ON AND NEVER HAD ANY PROBLEMS UNTIL NOW.HERE ARE MY 2 PROBLEMS.WHEN I TURN KEY ON-ENGINE OFF TO PRIME FUEL LINE,THE FUEL PUMP CONTINUOUSLY RUNS INSTEAD OF PRIMING THE LINE FOR A FEW SECONDS AND THEN SHUTTING OFF.MY OTHER PROBLEM IS WITH A TEST LIGHT ON EACH INDIVIDUAL INJECTOR HARNESS,MY INJECTORS ARE NOT PULSING,THE LIGHT JUST STAYS ON STEADY,NOT FLASHING OR PULSING.I HAVE CHANGED FUEL PUMP,RELAY,THERE ARE NO LEAKS INSIDE THE TANK OR ON ANY OF THE FUEL LINES OR RAILS.WITH KEY ON PRESSURE HOLDS STEADY AT 40PSI.AS SOON AS YOU TURN THE KEY OFF PRESSURE DROPS TO ZERO WITHIN 4 SECONDS INSTEAD OF HOLDING RESIDUAL PRESSURE FOR HOURS LIKE IT NORMALLY DOES.CHANGED REGULATER,IGNITION MODULE,AND CHECKED GROUND WIRE COMING OFF OF FUEL INJECTION HARNESS THAT BOLTS TO BACK OF HEAD.FUEL IS ALSO PRESENT IN FUEL RAILS BUT NOT GETTING IN AND THROUGH INJECTORS.NO WET SPARK PLUGS,MAKING IT OBVIOUS THAT FUEL ISNT MAKING THROUGH INJECTORS.IVE HAD A COUPLE PEOPLE TELL ME IT MIGHT BE A SHORT IN MY ECU.I KNOW WHERE MY ECU IS LOCATED BUT CAN SOMEONE TELL ME WHERE THE ECU POWER RELAY IS LOCATED ON A 91 GT.ALL OF THESE PROBLEMS ARE CAUSING MY STANG TO TURN OVER BUT NOT START.I DID SPRAY SOME STARTER FLUID IN THE THROTTLE BODY TRACT AND THE CAR RAN FOR A FEW SECONDS SO I KNOW THE IGNITION AND TIMING ARE WORKING PROPERLY.HOPE SOMEONE CAN DIAGNOSE THIS FOR ME.I DO HAVE A CODE READER FROM AUTOZONE,BUT I CANNOT PERFORM A KOEO TEST WITH IT DO TO THE FUEL PUMP CONSTANTLY RUNNING.PLEASE CAN SOMEONE HELP.THANKS FOR ALL OF YOUR INPUT REFERRING TO THIS SUBJECT.THANKS GUYS AND GALS.WBROCKSTAR:shrug:
 
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Test light stays on when testing the injectors means the ECM is holding the injectors open. Thus the reason why your pressure falls like a rock. Its an ECM issue, as nothing else controls the Injectors.

Try and pull the codes.
Might want to open the ECM up and look for a burnt trace on the back side of the board by the main connector. And check the blue capacitors while you are in there.