As reference for those reading this thread.
My
Scangauge is never accurate, always reads to much fuel flow on higher flow rates and to low of flow rates at lower flow rates. Basically the Curve is off. Likley a Diesel Only issue . . .
Some suggestions for attempting to nail it down.
1) only change your mileage 1/2 of the way to what it should be, eliminates "bounce"
2) Keep on trying
Of course out of the 5 Vehicles I'm normally in with
SGII's only 1 (the golf) has an issue.