KR does infact mean knock retard. When the knock sensor tells the PCM it hears knock, the computer will pull timing from the ignition. GM 3800 S/C motors fight a lot with knock. Increasing the boost will cause more knock because the incoming air is hotter, and under higher PSI. Tuning is critical on these motors, they typically need reduced timing and lots of fueling to fight off the KR and harmful detonation. KR is so bad because it really hurts performance. Every degree of ignition advance is worth between 1 and 3hp. So, if the computer pulls 10* of timing, there goes 20-30hp. And the recovery from KR is slow, so it doesn't add the timing back in very fast. They usually hit KR right after a shift and then the second gear sucks because its slowly restoring the timing. And if you're seeing KR, you're very close to, if not detonating, which is very harmful. Hope that helps. I know the GM stuff a lot better than the Ford, I learned a lot about the PCM systems when I did all the work on the Grand Am.
