Are you getting an IAB code witht he P72? Anyway, if you switch to a P28, chipped or otherwise, it won't be able to read the knock sensor. I would keep the P72, since they're getting pretty rare, unless you want to sell it, make a couple bucks, and get a P28. I wouldn't really want to run without a knock sensor unless you have your fuel and timing maps perfectly tuned(like with a standalone). Anyway, since your P72 is OBD-I, you can get that chipped if you want, or get Hondata S100 and get it tuned.