What would be the cause of white smoke coming from the exhaust in the 1999 Jeep Grand Cherokee v8 4.7?

blown head gasket. the easiest way to tell is to open the radiator cap while the cars running BUT BE CAREFUL! if theres antifreeze in there it will spray and burn you! but if you have a blown head gasket when you open the throttle the same white smoke will blow out of the radiator cap.

white smoke is a sign of a blown head gasket though.