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computer MPG adjustment

Here's an update on recent attempt to adjust my '91 200q board computer
fuel economy (fuel mileage) output. It was consistently reading about 10%
too _low_. So last week when the tech was removing the dash to replace
lightbulbs, I asked to have the fuel mileage adjusted to read higher by
10%. I commented to him that I recalled the description of the procedure in
Bentley was a little confusing about what direction the adjustment (3 mini
slide-switches) needs to be. He said yeh, he'd have to re-read the Bentley
to see what needs to be done. A while later, when I looked out, he had
finished up and said to me, "I adjusted your computer 10% higher."  I said

Well, one tankful of fuel later, and it appears that the computer MPG now
reads about 20% too low!!

An erroneous adjustment can occur owing to the fact that Bentley calls the
adjustment a "Fuel Consumption Factor", whereas we "Muricans" don't really
think in terms of fuel consumption (gal/mile), we do our inverse
"miles/gallon" thing. I guess Bentley _really means_ "Fuel Consumption
Factor". Hence if a USA model has an MPG reading that is 10% too low, it
means that the FCF needs to be DECREASED (not increased!) by 10% in order
to compute a higher MPG.

'91 200q
'89 100