Originally Posted by ChicoJeepy
1990 and before used a carburetor. 1991 and after was fuel injected.
All 2.5L YJ's are Fuel Injected from the factory.
1987-1990 use a Throttle body Injection setup (TBI), which has one big injector inside of the throttle body.
1991-1995 use the modern Multi-Port Fuel Injection setup (MPFI) which nearly every gasoline vehicle is designed with now. It uses one injector per cylinder, 4 in total, rather than one big injector.
Nobody makes aftermarket parts for the TBI, only the MPFI.
The change came when Chrysler decided to change the original 1987-1990 TBI design by AMC. Chrysler basically did a lot of re-designing for the 1991 model YJ.
1987-1990 6 cylinders were the carbureted 4.2L, 1991-1995 6 cylinders were the modern Chrysler 4.0 MPFI design.