Quote:
Originally Posted by RedFRS4me
The problem is I ran stock tune and code P0420 shows up but I still have the same issue with AFR dipping to low 13s. I park the car and the next day its back to normal. I drive it in stop and go traffic and it doesn't do it. Only when I stay at 60mph+ for longer than 30 mins that I start seeing the AFR dip slowly till I get stuck in open loop. LTFT and STFT stay 0% Just like OP
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I just resolved my issue (posted in the datalog review thread).
http://www.ft86club.com/forums/showp...postcount=1228
Turns out I needed a new rear O2 sensor. As part of my troubleshooting I unscrewed/screwed the O2 in and out a few times to make sure the threading was smooth and sensor flush (it was). So I knew it wasn't a sensor placement issue.
Also, before I bought a new sensor, a friend had an old O2 sensor laying around. Since it was free, I swapped that one in, and noticed the problem accelerated - it only took a few mins of cruise to start seeing the AFR's drop. I'm guessing that sensor was highly degraded (friend replaced it as part of troubleshooting larger issues, but it was old and had a lot of mileage).
So that demonstrated to me that a more degraded sensor could make the problem worse, and that the rear O2 performance had a pretty significant effect on AFR. I bought a new sensor and that fixed the problem - steady 14.7 cruise during extended 70+ mph cruise.
Keep in mind O2 sensor voltage always reported something reasonable and there were no codes thrown, so it's possible that these things can decay and affect performance without any other indication that something is wrong.