I would check the knock sensor harness itself. Test the wires from one end to the other. Should be low to zero resistance. Then test between both pins on one side, that should be infinite or open. That would indicate there are no wires touching inside the harness.
Do the same for the EFI harness to the ECU and the results should be the same. If they are then that would indicate possible ECU issues. If they are different, then that would say your EFI harness probably has issues.