In the middle of a swap, and I took the two o2 sensors off because I didn't want them to get damaged as I was putting the manifold/downpipe back onto the engine. Now, I can't remember which one goes into 1&4, and which one goes into 2&3. You would think it wouldn't matter, but each one goes to a different pin on the pr3 ecu, so I would think the ecu knows which one should be on 1&4 and which one should be on 2&3. It does matter which one goes where, does it not?