flexfuel flex fuel ncg3 ncg4 ncg4a

Question 1: how did flex fuel work on the early systems, sensor like GM used Question 2: what's the difference between an NCG4 and NCG4a ECU? Background.. dodge offered FlexFuel as an option on some on some 2.7l v6 and 4.7l engines starting in 2007/2008 using a ECU NCG4 ... Extra points...