I believe the ECU is grounded through the main engine ground to the intake manifold so you could check that.There are documented problems with poor ground connection there. The ECU supplies a ground path for ignition power to the FP relay, thereby enabling battery power to the fuel pump. Faulty ignition power? You really need a 12v test light and multimeter to be diagnosing this. With the two green test connectors connected and key turned to ON, the relays should be clicking and fuel pump cycling. The fuel pressure would cycle between 40 and 45 psi with no decay below 40 with a good regulator on my 02 2.5L. There are other tests to diagnose fuel pressure problems as well. The CELs you are getting is a concern. Maybe your ECU is going tits up or it's a ground to the ECU issue.
Edit: What CEL codes are you getting? If you don't know how to check look for YouTube videos on how to.
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