Can i swap a 1990 fuel injected full size blazer computer with 1986 GMC fullsize jimmy?

No, you can't directly swap a 1990 fuel-injected Blazer's computer with a 1986 carbureted GMC Jimmy's. The 1986 Jimmy likely has a carburetor and no computer for fuel management, while the 1990 Blazer uses a sophisticated electronic fuel injection system controlled by its computer. The wiring harnesses, sensors, and even the engine itself are completely different. The 1990 computer would have no way to communicate with the 1986's system.