Are you a Big-Rig Hypermiler ?...

[SquareOne]

Thought I'd revive an old thread as it def pertains to hyper-miling. As a refresher, I'm running 2 trucks, a daycab Freighiner Cascadia w/ 190in WB and a sleeper International LT625 (newer Prostar version is all the fancy numbers really mean) w/ a 226in WB. Both with new sets of drives BTW.

I try to squeeze every dime I can, especially when it comes to fuel. My Cascadia has very often achieved high 8-9.0's mpg since I've owned it with the International always staying about .15-.2 behind. I figured the taller roof and approximate 2k lbs of additional weight was to blame.

However (and I'll get to the point of the post), these last 3 tanks, I've actually beaten the Cascadia by a hair in the MPG race. The only difference - - - I've been IN GEAR (IG) coasting rather than OUT-OF-GEAR (OOG) coasting. The last 3 hand calculated tanks were 9.04, 9.05, 8.99mpg. I've always been an OOG coasting guy when I had to bring my speed back down to 60 from a decline which pushed me faster, but just recently I tried leaving it in gear with no throttle input.

Whenever I'm OOG coasting, the instant MPG (which I know isn't perfect) hovers around 45-60mpg depending on speed. The IG coasting immediately maxes out the instant mpg at 150.5mpg until I touch the pedal. My question after all of this is...

- Does the ECM go to near zero fueling when IG coasting due to the speed vs engine load and rpm, whereas OOG coasting requires the ecm to command enough fuel to stay at idle?

I may be waayyyy off with this assumption, but this is literally the only change I've made in order to try to achieve the Cascadia numbers. Loads, 60mph speed, weather, route, times driven, even the same truck stop and pump, etc. have all been nearly the same. I hand calculate each and every tank from both trucks, so any anomalies will be caught early on. Each tank is typically about 1250-1270mi between fill-ups, so if what I'm assuming is true, that's a pretty damn good improvement for just one small change. I waited for the 3rd tank numbers to come in before making this post, because it just seems too good to be true. In this case, I don't see how the numbers could lie.