I HAD A 86 305 TPI I BLEW IT SO I PUT IN A 91 305TPI AND NOW ITS SMOKKIN BLACK SMOKE OUT THE TAIL PIPE A MECHANIC TOLD ME IT COULD BE THE ECU SO I CALLED THE DEALERSHIP AND THEY TOLD ME ITS TWO DIFFERENT ECU'S BEING THAT ITS TWO DIFFERENT YEARS BUT FOR THE 91 305 THERES ABOUT 12 DIFFERENT DIFFERENT SELECTIONS HOW DO I FIND OUT WHICH IS BEST FOR ME?

 

Provided that you used all the stock sensors and wiring from the 86 the ecu should not have a problem controlling the motor. By 91 GM had changed the engine managment system to speed density as opposed to maf sensor but that was only the electronics, the motors themselves are not all that different from each other. The 91 has a roller cam and different heads.

Did you do the swap yourself, or did the mechanic do it?