I've discovered how to calculate the Air:Fuel ratio from the numbers in the Fuel Map. The formula is 14.7/(x/128).
So here is an updated diagram and an excel spreadsheet of the maps with the formula applied. I'll update the enginuity definitions on my website later today.
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Subaru ECU and TCU Website
1992 Alcyone SVX Version L
1992 Alcyone SVX Version L
1994 Alcyone SVX S40-II
2004 Subaru Legacy 2.5 SE Sports Tourer
1996 Subaru Legacy 2.2 GX Wagon
1988 Subaru Justy J12 SL-II