So just out of curiosity I wanted to see if someone can explain this magic to me.

My 89 V6 gets horrendous fuel economy. 11.8mpg is my average as per my last 10 fills prior to me leaving ect pwr on.

After I turned on ect pwr and left it on, I averaged just under 15mpg for the last 3 fills. Still not great, but better.

Can anyone explain that? I mean something happened. My general impression, however, was that fuel economy, if anything, should go down.

Anyway, I'm replacing my O2 sensor in a few, so hopefully I get a boost.

 

Gas engines are more efficient at higher revs. Power setting just changes gear change point to a higher rev point, so engine is actually working less.
Kind of strange to most practical thinking, but same reason why I get better mileage by not using 5th gear under 60 mph on my 94 22RE.
Just an under powered- over worked engine causing you to push pedal down farther to get same results.