Originally Posted by Fresh1
Well, here's a theory (to answer my own question ;) ...
Maybe when decelerating in gear, the vacuum generated by the piston downstroke sucks in blowby gasses back into the cylinder/combustion chamber, and then sends them out through the exhaust during the upstroke. So, maybe the Scanguage just "thinks" more fuel is being burned at this time, but it isn't? ...
I think you have yourself the answer, our F150 (With the "gas guzzling" 5.4) has this technology (as opposed to the multi cylinder displacement crap that GM and Dodge use) and it works. When deacelerating in gear in our truck, it effectively "shuts off" fuel to engine and uses road speed (and the transmission) to continue to propel the vehicle forward while coasting (as long as possible anyway). To keep the engine "running" without new fuel, it uses compression and EGR system. We do notice a difference by "coasting" in gear to stop signs etc... I bet the Scanguage is not configured with those parameters and is merely measuring the amount of vacuum in the intake.