So what I cannot see is if you disconnect the O2 sensors with a TTS tune? And if not, and the closed loop system is still engaged how can you apply a custom tune for all the time closed loop is engaged? It always going to try and achieve 1.0 lamda if the O2 sensors and closed loop is still active. What an I missing?
The missing part is that the TTS (and other flash-type tuners) can change the fuel map to obtain the desired lamda (AFR) in closed loop. So the O2 sensors are still "in the loop" lol, but now the system is injecting more fuel to get an AFR that is richer than stoichiometric (14.7 with pure gas, not with E10).
BTW, concerning HD and their warranty: HD will void the powertrain warranty if a non-EPA approved map has
ever been installed, and their ECU sets a "flag" when a different map is installed. Mastertune says its device can install a new map, then later re-install the original EPA approved map,
without leaving any trace. They also say PowerVision, FP3, and other tuning devices cannot do this, and leave a flag set that tells HD you've been a bad boy. FWIW