Both ethanol and winter-blend rfg have lower energy content than summer gas, with more oxygenates. Both together is a double hit. Since the Scangauge only measures airflow, it doesn't know that the ECU is adding a little more fuel to the mix to make up the difference. You need to INCREASE the fuel offset % to account for this. (ie. without adjusting, it reads higher mpg than reality)
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11-mile commute: 100 mpg - - - Tank: 90.2 mpg / 1191 miles
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