I am going to have to have an o2 sensor bung welded on before I will be able to install one because of the custom y pipe. My question is, what happens if I drive the car around with no o2 sensor and gets to operating temp? I know in open loop the car relies on predetermined tables for fueling and spark and the o2 isn't used. If I don't have one plugged in, will it just stay in open loop the entire time? I would prefer to not have to trailer it to get the y pipe made at the exhaust shop (not in the same town as me) but if I have to then I have to. Plus I will be taking it around the block some to make sure everything works ok prior to spending the money to finish the exhaust.

So, aside from a code, what will happen?

 

You covered it, the ECM will stay in open loop and eventually set the SES and toss an O2 code. Other then that, nothing. As long as the tune is close enough to not require massive amounts of long term fuel corrections you can drive it.

RBob.