To tap or not to tap?

[Evan]

but do you really think that running without a proper o2 is going to allow the engine to compensate fuel trims in closed loop mode properly? You probably wont notice that much of a difference, but the difference is there, the ECU is no longer monitoring so lo and mid fuel trims are going to be a guesstimate on your o2 simulator.

I agree to a certain extent, but I also think that you are over exaggerating the role that an o2 sensor plays, at least in an engine /ECU like mine that was originally designed for pre ODB days. Exact optimal fuel mix? Probably not (but o2 sensors arent that accurate anyway) optimal power and fuel economy? probably not. Enough to any damage or any adverse affects, no way.
In the more complicated world of forced induction ECUs the o2 sensor plays a larger role, I have no doubt.