My FI Sedan has been running at 16 mpg consistantly for a while,

After a hard day at drag track, it now came back up to 17.5 mpg.
(I was getting 18mpg before FI). It's been two tanks now. The
mpg improvement is obvious.

At the end of track day, I got Cel light that says running rich,
I think the factory ECU must did some kind of self tunning, so that
it reduced fuel consumption.

Have anyone seen this?

 

when the ECU increases timing, that makes your fuel efficiency go up. But it might have increased fuel too.

 

I envy you, im gettinng 15mpg with the stillen kits. I've tried not getting on it at all but get the same mileage all the same

 

Take it to the track & do a few hard 1/4 mile runs,

You'll be having AFR in the 11s for a while & it'll triger cel light for running rich,
That way, your ECU might self adjust & you may get better mpg after reset the cel.

I am curious if this experience is repeatable by others.