1991 off set

can anyone tell me the purpose of the air induction valve inlet on a 1991 na exhaust. I reciently bought a 93 for parts and was changing the exhaust and they are way different. I took the hoses off the 91 exhaust and welded them on the 93 so it would be correct. Running better and sounds way better. Just trying to find out the purpose of these. 2nd question is: can I use the ECU from the 93 and put it in the 91. I have one plug not firing and was believing it was a bad injector but after reading some stuff here i believe it could be the ECU. Would like to switch that out before going through the he## i have heard the injectors are to change out. Thanks.