91 Z32 Fuel delivery issue
 

I'm having an issue with the fuel pump pumping enough pressure to the rail. So far I've replaced the fuel pump, FPCU, most of the fuel lines, and pressure regulating valve, also I Checked the fuse and fuel pump relay and they're both fine and still no luck :( This all started because the car took several cranks to start, especially when it was cold. Once I replace the fuel pump it completely lost the ability to start and fuel delivery to the rail. Since then I replaced the parts listed above and have had no luck. When I attempt to start the car I hear the pump running but the car doesn't start up. The only way the car starts is when I have jumper cables from the cars battery hooked directly to the fuel pump using connectors to the pump wiring harness. If anyone has any idea what I can try next please let me know