Using a logging tool to log your exact RPM, pull the injector wires for the suspected cylinders. If it makes absolutely no change in rpm then take off the fuel rail switch out the bad ones for either a known good one from a seperate car, or swap a known good one from a differant cylinder then try again. If it's the injectors the problem should switch cylinders following that particular injector.
Come back with your results of that test. If it is indeed a fuel problem, we can then help you more.

If it's not getting fuel in cylinders 2 and 3, why do you ask how the knock sensor would make it feel on only 3 cylinders?