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A/F Learning Ranges

From Bill@COBB:
"A/F Learning 1" is simply the currently applied long-term fuel trim, which would be one of the A/F Learning 1 A, B, C, or D values. Those values are determined and applied across different Mass Airflow ranges. So, for the 02-05 WRX, it would be something like:
0 - <5.6 g/s = "A" Range
5.6 - <10 g/s = "B" Range
10 - <50 g/s = "C" Range
50+ g/s = "D" Range
So, if Mass Airflow shows 5 g/s, given the above example, "A/F Learning 1" would be applying (and show in log) the values stored in A/F Learning 1 A. If Mass Airflow was 8 g/s, then it would be showing A/F Learning 1 B, and so on. The advantage of looking at A/F Learning 1 A,B,C,D, say via live data, is that you can quickly check all 4 without a data log that would requiring you hitting all these Mass Airflow ranges (which would be the case if you were just looking at "A/F Learning 1"). In fact, you can check these A,B,C,D values with the engine OFF ignition ON. So, if you suspect a fueling issue, you can drive around until A/F Learning 1 values populate accurately, and then simply check the A/F Learning 1 A,B,C,D via live data without worrying about a driving data log with just "A/F Learning 1". Keep in mind that the A/F Learning 1 values are all cleared when you install/uninstall AccessPORT, reflash a map, reset the ECU or disconnect the car's battery. They will then need to drive a bit for those to populate more accurately (usually drive through about a full tank of gas).
Most WOT data logs will hit A,B,C,D, so it usually isn't necessary to look at A,B,C,D individually. A WOT pull will definitely hit "D" and when they let off (or before the run), you'll likely see a progression up or down through A, B, C. "A" can be the trickiest, but if you lift off at the end of the WOT run and data log that for a little bit, you'll usually catch it. 
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