Ford Focus Forum, Ford Focus ST Forum, Ford Focus RS Forum - View Single Post - Optimizing Accel and Decel
View Single Post
Old 09-06-2012, 07:10 AM   #29
kam327's Avatar
Join Date: Feb 2012
Fan#: 94700
Location: Tampa, FL
What I Drive: '17 Mazda6 (traded in the Focus)

Posts: 2,713
Points 14,511, Level 78
Points: 14,511, Level: 78 Points: 14,511, Level: 78 Points: 14,511, Level: 78
Level Up 16% Completed
Level up: 16% Level up: 16% Level up: 16%
Forum Activity 18%
Activity: 18% Activity: 18% Activity: 18%
FF Reputation: 15 kam327 Great Standing Member
Buy-Sell-Trade Rating: (0)
Originally Posted by Fresh1 View Post
I think the OP wanted to test the effectiveness of fuel cut-off during deceleration. This is why it's strange that the fuel consumption was higher in gear. If the fuel is cut off (regardless of engine RPM), it should burn NO fuel - vs. engine at idle speed in N. Anyone know what's goin' on? ...
It can be explained very easily. The main assumption here is that you have to travel further at speed before coasting in gear in order to reach the stop sign at the same speed you would reach it coasting in neutral, since you'll decelerate more quickly in gear than in neutral.

The Focus burns say roughly 0.3 gal/hr at idle, and roughly 1.3 gal/hr at 45 mph (I'd have to confirm these numbers but rough order of magnitude they're pretty good).

In the coast in neutral scenario, you're burning 0.3 gal/hr for the full 60 seconds to the stop for a total burn of 0.005 gal. In the coast in gear scenario, you're burning 1.3 gal/hr for say the first 20 seconds and then 0 gal/hr for the next 40 seconds for a total burn of 0.0072 gal, a 44% increase over the coast in neutral scenario.

Originally Posted by pozi240 View Post
^ This
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.
Yes of course there is a difference by coasting in gear versus speeding up to a stop and then slamming on the brakes. The point is that theoretically you can do slightly better by coasting in neutral.
kam327 is online now  
    Reply With Quote