alright i have an apexi safc 2 on my s 4 na ... and when i hooked it up there was no wire at the ecu for a knock sensor reading ...... so i just left it unhooked .... the fuel computer works fine BUT i still have a knk reading ... wtf is that ?... how is it doing that /.?

 

Your knock wire is acting like an antenna & picking up electrical noise.
Just ground it.