hello everyone,
i just joined to see if u guys can help me out. i just swaped my 305 tpi on my 86 iroc to a 1989 5.7 350. it runs fine with the old 305 ecm and prom but it does back fire a little and it runs really rich. i was told to swap the prom, so i did and now my car wont start. but if i swap back to the 305 prom it turns on just fine. i also changed my 305 esc to the 350 one. any suggestions???? thanks Joel.

 

I'm doing something similar and came across this article: http://tpiparts.net/305_tpi_to_350_tpi_conversion

I called the guy and he said you need to change the prom, knock sensor and probably the injectors.