^exactly...
pcb...when the UG people are talking about multiple O2 sensors...they're not referring to a set up like ours...There are some OBD-II equipped cars that actually have 2 engine computers entirely (the E39 BMW 5 series V8's to name one; it had a computer controlling each bank and set of throttle bodies)...and therefor multiple 'primary' o2 sensors...Our cars only have 1 o2 sensor that the UG should be worried about, the other one is just to moniter catalyst performance...as mentioned...
As far as the government...ideally a car should be in closed loop all the time...but processor resolution and sensor expense hinders that...open loop is needed because as load and rpm rise, there is less actual time to make the adjustments need to richen the mixture...which is why a system that uses data from a sensor AFTER the ignition event...becomes problematic...newer cars, and some full blown aftermarket stand alones...can do a high load closed loop protocol with a wide band o2 sensor and an extremely powerful central processing unit...a far cry from the calculator we have in our cars as standard...
I don't specifically know enough about these ecu's to know what exact sensor are used between the 2 loop modes...PCB, in theory, yeah...when the pcm goes to open loop, the data from the primary o2 sensor is arbitrary for fuel requirements...the ecu will still correlate data between BOTH o2 sensors, but ONLY for monitoring catalyst performance...when open loop is in place, the oxygen ppm of the exhaust gas will be outside of the primary sensors range for adjusting requirements, because everything is happening too quickly...but the computer can still compare what the first sensor sees with what the 2nd one does, if that makes sense...
and that is news to me about closed loop coming in just a minute or so after start up...I had read some Mazda tech documents a few years ago that explained how the VTCS functioned...and that it was part of an integral 'cold start' protocol the ecu would go through...which remained until the engine was warmed up past 149*F iirc...at that point the ecu triggers the opening of VTCS through vacuum assist...and normal operation is underway...it didn't specifically say if it was an open or closed status (when VTCS was activated i mean)...but implied the engine wouldn't be in 'normal' closed loop until almost fully warmed up...
what we can definitely say:
the ecu HAS to have some sort of cranking map for cold starts...When temps are extremely cold, many members with a VTCS delete have reported problematic starting and idle...that doesn't go away until the engine begins to warm up (several minutes at least when in below freezing ambient temps)...
however...those running an MP3 ecu (or just the car for that matter), which doesn't have VTCS to begin with...there is NO trouble starting in very cold situations...i can attest to that, 2 weeks ago my car fired right up in temps around 0*F with no trouble at all...and idled just as it always did...While i do currently have the VTCS system in tact, the MP3 ecu isn't using it..the solenoid never moves the arm connecting to it under any situations...so that proves that the 2 NA ecu's definitely do have different methods for cold starts, at least...