I live in the mountains, and have one 8-mile stretch down hill where I like to use engine braking to keep from riding the brakes all the way down. I've noticed something interesting, in that the ECU appears to be feeding fuel to the engine when I have my foot fully off the accelerator--so I get much less braking than I should. (Some modern cars cut-off the fuel entirely during engine braking--but not the Aston). I select "Instant MPG" on the computer, leave the car in 6th gear, and it shows "99.9". Every so often, I feel a little forward surge and the IMPG drops to "~65", then a few seconds later goes back to 99.9. If I down-shift to 5th the IMPG drops to about 65, in 4th it drops to about 47, and in 3rd drops to about 35. So even shifting to lower gears doesn't help much with braking because the ECU is compensating by feeding in extra fuel--Bummer.

 

I've noticed the same thing see - https://www.6speedonline.com/forums/...dfco-help.html