active fuel management?

I know this has been around for a while, mostly in luxury cars, which is why I never really cared enough to read into it. But how exactly does the car just shut off 4 of the 8 cylinders under lighter loads to save gas? Does it just cut out 4 of the injectors and then just "lug" (as in just spinning the other rods and pistons without them doing anything, kinda like when you got dead plugs) the other 4 cylinders?

No there are special lifters with unique oil circuits. The PCM turns on a solenoid that cuts off oil flow to 8 of the lifters, shutting down 4 cylinders. The injectors turn off as well. As soon as you put your foot back in the gas the solenoid switches off and the lifters pump up again and the injectors come back on line.

The pistons are stull moving, but there's no air moving in or out of those cylinders and no fuel being squirted either.