Just finishing a swap and my exhaust is not done, manifolds are on, no downpipes or O2 sensors though. If I plug the O2 sensors into the harness but they're not in the exhaust, will it start ok and just remain in open loop?

 

It should run even without the o2's plugged in, mine did, since the o2's aren't reading in open loop when the motor is cold, it doesn't even matter if they're plugged in. Like I say, mine started up and idled fine with none plugged in

 

You will be better off leaving them unplugged then plugging them in and letting them hang. The PCM will recognize they are faulted out and won't even attempt to use them.

 

Thanks!