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Originally Posted by RedFRS4me
I see. Good info to know. I just find it odd that I've been running the OFH for almost a year and only this past weekend did I get this issue. Coincidently it happened when i decided to swap from e85 to the new OFH tune and went on a 800 mile trip that I saw this for the first time. I'm pretty anal about my readings when I switch them and it just baffled me. What's also weird is it only happens if I'm cruising on the hwy (about 65-75) for longer than 30 minutes, I start noticing the AFR drop and my STFT stop working. If i'm driving in intervals of 10-20 minutes it doesn't go haywire at all and everything is good.
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When stft goes to 0 it usually indicates open loop fueling mode, open loop is usually during hard acceleration and wot.
if your jist cruising on highway then your usually in closed loop fueling mode and stft should be varing and commanded afr and afr should be very similar.
sounds like something weird is happening and ecu is going into full time open loop, it might be because of the rear 02 sensor or exhaust leak or something else not sure
if the logging is set up for your rom the oft can monitor the rear o2 sensor its labeled in oft log as "wideband AFR", its actually calibrated for use with an aem wideband sensor but it should give you some idea if the rear o2 is actually working.
if you had to use excessive force on sensors to install then in header it can damage them, if they are not screwed in all they way they can leak causing weird issues as can exhaust gasket leaks