P0001 OBD2 Fault in 2013 Ford F150 3.5L EcoBoost: Misfire at High Throttle, Code Persists After Replacement Parts

Hello everyone, I recently purchased a 2013 Ford F15-0 with the 3.5L EcoBoost engine and am experiencing a persistent issue that I'm trying to resolve. Last week while driving home from work, I noticed a misfire, especially when accelerating beyond 30% throttle. I switched the transmission into manual mode to test if the misfire occurred across all RPM ranges — it did, worsening with increased throttle input. Since there was no Check Engine Light (CEL) initially, I suspected poor fuel quality and drove the vehicle for several days without any improvement. I drained the tank and refilled it three days ago, but the problem persists. The issue appears to be triggered specifically when throttle exceeds 30%, with a noticeable loss of power and rough idle. The OBD2 scan tool detected code P0001 — Fuel Volume Regulator Circuit Open. I replaced both the high-pressure fuel pump (which had a loose male connector in the original harness) and installed new Motorcraft spark plugs as recommended. After reassembly, the symptoms remain unchanged. Interestingly, I can no longer clear the P0001 code through the OBD2 system — it now shows as 'permanently stored,' even though the CEL is off. I took the vehicle to a trusted mechanic I know — his father owns a shop with proper diagnostic equipment (not a basic AutoZone tool). He inspected all coil packs, rear fuel pump, and other components. His conclusion was that either there's a wiring fault in the harness leading to the engine control module (ECM), or the ECM itself may be faulty. This is my first experience with direct-injection engines, so I'm somewhat unfamiliar with their intricacies. While I’m confident in my mechanical skills, I'm now considering using a multimeter and continuity tester to inspect the wiring harness for breaks or poor connections — especially along the path from the fuel volume regulator to the ECM. Before proceeding further, does anyone have experience with this exact P0001 issue on a 2013 F150 EcoBoost? Any specific wiring routes, known failure points, or troubleshooting steps that could help me diagnose it more effectively? Thanks in advance for any insights or advice!