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could someone explain the closed loop o2 sensor...
does this affect my safcII????i think i read somewhere that at cruising youre o2 goes into closed loop mode and the safc is useless at this time??? i also thought i read somewhere that they disconnected the o2 from the ecu so that it wont do this???? wouldnt this affect the ecu and make it go crazy??? should i need to worry about this if i need to tune my injectors fo my n/aturbo??? ill be runnin 550's and 720's.
One question mark is fine, 3-4 is excessive. Trying to make sense of your questions:
At a light throttle cruise (below 3500 RPM and light throttle), the ECU does use the O2 sensor and ignores the airflow meter. This means that the SAFC-II is not controlling anything, because the signal it tweaks is being ignored.
I'm one of the people who removed their O2 sensor input. I'm debating reattaching it, to see what sort of effect it has, but I'm getting 20-24mpg highway without it right now. The best I ever saw with it was 26mpg, but that was with a stiff tailwind. I also can't cruise at my most efficient speed due to a bit of a "get another speeding ticket and lose your license" issue.
The ECU doesn't really care if the O2 sensor is missing. It'll throw an error code on the S4, and may light the Check Engine light on the S5 (not sure, I don't have one to play with yet), but it'll run fine. It ignores it most of the time anyway.
Running 550s & 720s on the NA ECU is going to be a bit of a stretch with a SAFC, IMO. It runs stupidly rich as is, and you'll just be making it run richer.
Let's say your afr's are 15.5 afr when cruising around at 65 with the 02 sensor disconnected. Now you decide to reconnect the 02 sensor and cruise at 65. Your afr display won't show 15.5 anymore, it'll show in the 14.7 afr range. And you'll possibly feel a bit of hesitation. Just a tad. Disconnect the 02 sensor and leave it off.