IDriveHonda

Here is the deal, I have been collecting parts here and there forever to do this mini-me project and I am almost ready to actually do some work. I have a 99 CX 3dr Y7 block, Y8 head/mani, 95 EX tranny, 99 Si wire harness, and currently a 99 EX ecu. I am thinking of purchasing an obd2b-obd1 harness and running a p28 for better tunability because I eventually want to go turbo. I know that the Si and Ex have a O2 on the cat and the wires go through the floor and join to the interior harness. If I go to OBD1 do I need to worry about this secondary O2 at all or will the conversion harness just use the primary one? Sorry for the detail but I think it is better to know all the facts to give a good answer. Any help is appreciated. Thanks.