wont start cold?
 

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!!

Ignition Switch?
 

First thing I would check is the ignition switch. Causes many electrical problems, often intermittently and is a known problem area. Next time you have the problem, try cycling the switch fully off and then back on to see if it will then start.

I have just had my car fixed (1999 Boxster) with a similar problem. Ask your mechanic / Porsche dealer to check the the Air Mass Meter is not faulty - it may sending incorrect readings to the cars management system (bare in mind I am not a mechanic!!)

Check that the Air Mass Meter is functioning properly!

you can first clean the MAF sensor with MAF spray cleaner (buy at any auto part store). it may just be dirty. if that doesn't help, then see your mechanic. i doubt it is the ignition switch or you will have other issues like lights or radio not working correctly and you will have trouble pulling out the key from the ignition.