I was wondering if this was true or not? I would think I just misunderstood what was posted on another board. I would think the way afm works is the lifters pump up just as much with afm off. It is just that the cylinders do not fire. You are carrying around dead weight since the pistons and valves are still opening. That is way afm is not a true 4 cylinder type mechanism and it is just worth a mile or so per gallon more when activated. I do notice a slight vibration when it kicks in since I changed to a custome x pipe.