The 4wd system on the RSX will not engage unless you are under 8 mph. It's done that way to prevent people from having both back wheels spinning (in mud or snow) and then turning the front wheels on and possibly tearing up the front differential or 4wd shifting mechanism.
Let's say you are going 30 mph and turn the dial. it will nto shift until you slow down to 8 mph. At that point it will go in by itself and stay there until you turn it off. It sort of goes into a "waiting mode" until your speed gets down to 8 so you don't have to worry about cycling it on/off.
It will obviously STAY in 4wd at any speed - just need to be under 8 to engage it.
If you watch your instrument cluster you will see the little 4wd symbol flashing until the parts are actually engaged. The light should then be on solid.
So it is "on the fly" - if you're flying slow...
