About a month ago I installed FX4 rims and 285 tires on my 4x4 STX. THe 1" diameter difference in tire height was immediately noticable on power and the truck bogged. Also, my low fuel light came on at around 250 (vice 300 with the stock tires).

Over the past 5 or so fill-ups since the tires were put on I've gotten progressively better gas mileage

Tank 1: low fuel light at 250
Tank 2: 250
Tank 3: 261
Tank 4: 270
Tank 5: 291

Also, the shift points feel a little tighter.

Coincidence?

 

I would imagine it is possible. During my dark times I owned a few GM cars that would "learn" to either be in performance mode or daily driver mode. The only problem is to keep it in the performance mode you had to drive it hard all the time.

 

some high end cars have had this feature for a few years (MB, BMW)

 

I thought all cars had this feature by now! My 95 and 96 Impala SSes had this feature. To reset the learn function, you simply unhooked the ground on the battery for about 20-30 minutes, or just pull the pcm fuse.

I would assume the procedure on the F150 is the same.

 

Do I correctly recall an early thread on this forum that mentioned that the ECM is flashed at the factory to account for whatever differing combo of tire/rim size is installed? I think the author of the post mentioned that he had the dealer reflash the ECM for the max OEM tire size when he installed larger tires.

 

Yes, your vehicle "learns" your driving habits and adjusts it's shift schedule accordingly. Ford has been doing this for a while and IIRC, it's even mentioned in the manual.

 

No, wasn't me. I haven't unhooked the computer either.

Maybe it's a few different factors, but it definitely feels like it's bogging less and the fuel efficiency had definitely improved.