With a piggyback ecu, is it correct to still leave the primary o2 sensor in? This is so the stock ecu can still make open loop adjustments, right?

I am planning on putting 3 o2 bungs on my exhaust then. Primary, secondary, and wideband. I'll be using the greddy ult along with boost. Even if I hookup the wideband to send output to the greddy, the stock ecu still needs the primary o2? I was under the impression that when tuning, you also tune the partial throttle map which makes me wonder why you would still need open loop. or is that only for standalone.

Sorry if im not making sense, im not thinking straight today

 

Better yet. Use the wideband to simulate the narrowband that the ecu needs for closed loop. The ultimate can do this and in the process trick the ecu into a different closed loop target