fuel problem--regulator or injectors??

[titotonto]

Hello,

I have an sr20det in and 89 240sx. I recently upgraded to a walbro 255lph fuel pump, and now the car has lots of trouble starting. It will start but when you shut it off, it wont restart unless you disconnect the fuel pump. then it will run until it uses up all the fuel in the system. When it is running it runs fine, perfect timing, no smoke, no trouble codes from the ecu----This leads me to believe that somehow the fuel pressure regulatr is malfunctioning---any suggestion??? Thanx.