wont start cold?

[P-51 Mustang]

Help!! I have a 2001 Boxster that fails to start on occasion. To date, I have replaced the fuel pump and the inline fuel filter. I have placed a pressure gage on the fuel injector bar to monitor the pressure. When the car runs, the pressure remains solid at approximately 45 psi. When the car fails to start, the pressure is zero.

Failure of the car to start usually occurs after the machine sits overnight or for a period of 8 hours. The fuel pressure on the fuel injector bar is zero at this time and does not pump up with repetitive cycling of the ignition switch. I have verified that there is no electric power to the fuel pump during these no start periods. I can apply 12 volts directly to the pump and the pressure on the fuel bar goes to 45 psi. The car will then start.

I have replaced the fuel pump relay and the fuel pump fuse. At this point, it appears that the brain/computer may be faulty. Your comments on this problem would be greatly appreciated. Thank You!!