2021 Mach 1 Having High Pressure Fuel Pump Issues

Engine blew up last year. HPFP has been replaced, twice. We also tested a good known HPFP and still not building any high pressure. The pump isn't working at all. I'm stumped. Anyone ran into this issue after replacing a Gen 3? If so, what was the issue? This is a car we're tuning and I just would like the customer to be happy. Thanks in advance!

Make that the hose with the check valve that goes from the fuel rail to the high pressure pump isn't installed backwards. The side with the 90 deg bend attaches to the fuel rail and the side with the 45 deg bend attached to the pump.