I just installed a walbro 400lph and there is no fuel pressure...
I can hear the pump running but no pressure.

I checked that the red wire on the plug goes to +....

 

You need to check where the fuel pump is seated. The black rubber grommet that goes on the fuel pump is not inserted or seated properly. I found I had to modify the plastic collar to fit on the neck of the fuel pump and then insert the rubber grommet. Otherwise without the plastic collar, the rubber gromment will be prone to coming loose, thereby resulting in very low fuel pressure.

 

solved