I have a PCIII installed, obviously with the O2 eliminators installed, the ECM is running in OPEN LOOP 100% of the time. I also have a SERT (not currently being used... LONG STORY!!!) The SERT allows for CLOSED LOOP operation in the "cruising" range. Question for any techies out there... What are the advantages/disadvantages with the ECM running in closed loop operation? Is it just EPA/CARB requirements? Fuel economy? Any comments/help would be appreciated.