I just got done with my k20 ef swap. I was cranking it with 60 PSI and I got a code to change my O2 sensor. I did lower the pressure to 45 ish. I changed the O2 sensor and tried to turn the engine again. The engine turned but would not turn on. Checked my pressure and it was at 0. I turned the key to off and back to II postion and could not hear the pump prime? Any ideas as to where to start looking?

 

that sounds like the main relay, it should click every time you turn the ignition to the on position, and the fuel pump should "hum" for a second as it primes.