From the way that it's been explained to me, our cars don't fire 2 cylinders at a time. The spark does fire, but one of them is on the compression stroke and the other is on the exhaust stroke. I havent visually checked the cam lobes to confirm this myself, but that's what I hear... When the J&S knock sensor detects knock on a cylinder, it knows when that piston will be on the compression stroke and when it is on the exhaust stroke. Therefore, it knows which spark to retard (the detonating cylinder on the compression stroke) and which spark to leave alone (the other cylinder not detonating). This goes for both cylinders 1 and 4 and cylinders 2 and 3. That is the only way that they can pull timing on an individual cylinder basis with a 2 coil ignition.

You said that both pistons fire at the same time... Are you absolutely sure about this, because if that is the case, then it would seem to me that individual cylinder timing would be out of the question, and that would suck.