Coasting with a Slushbox - Fuelly Forums

Android Users - Coming Soon! - Migrating from aCar 4.8 to 5.0

Reply
 
Thread Tools Display Modes
 
Old 10-03-2007, 07:33 PM   #1
Registered Member
 
Join Date: Aug 2007
Posts: 313
Country: United States
Coasting with a Slushbox

When coasting with the engine on:

I've heard others claim that coasting in drive is more efficient because the injectors cut off, but I can't see the engine being dragged in a non-burning state for very long, and the glide is much much longer in neutral. I have been coasting in neutral and think I get better FE that way.

Does anyone have a good link that explains how FI systems work on cars with and without automatics when they are coasting?
__________________

__________________
2TonJellyBean is offline   Reply With Quote
Old 10-03-2007, 07:40 PM   #2
*shrug*
 
Join Date: Sep 2005
Posts: 6,195
Country: United States
I think automatics usually leave the injectors on, at least mine used to...but I can't get more technical than that.
__________________

SVOboy is offline   Reply With Quote
Old 10-03-2007, 07:58 PM   #3
Registered Member
 
omgwtfbyobbq's Avatar
 
Join Date: Jul 2006
Posts: 1,516
Country: United States
It idles.
__________________
Quote:
Originally Posted by FormulaTwo
I think if i could get that type of FE i would have no problem driving a dildo shaped car.
omgwtfbyobbq is offline   Reply With Quote
Old 10-03-2007, 08:00 PM   #4
Registered Member
 
Join Date: Aug 2007
Posts: 313
Country: United States
I trust everyone's judgment and appreciate your responses but are there any good links that you know of?
__________________
2TonJellyBean is offline   Reply With Quote
Old 10-03-2007, 08:14 PM   #5
Registered Member
 
skewbe's Avatar
 
Join Date: Jan 2007
Posts: 771
Country: United States
Sure, http://www.gassavers.org/search.php

Really it depends on who was doing the programming on that car. Some leave fuel running, some dont, some even add extra fuel. It varies by model. If you want to be sure then you have to monitor the pulses sent to the injector under various conditions.
__________________
Standard Disclaimer
skewbe is offline   Reply With Quote
Old 10-03-2007, 08:20 PM   #6
Registered Member
 
Join Date: Oct 2005
Posts: 1,978
Country: United States
Quote:
Originally Posted by 2TonJellyBean View Post
I trust everyone's judgment and appreciate your responses but are there any good links that you know of?
Not to be rude,
or a party pooper,
or a poor ombudsman,

but there are some experiments and/or threads here at GS that address this very data inquiry.

Over 2K RPMs, autos generally cut fuel in D. In N, it idles and uses fuel.
__________________
rh77 is offline   Reply With Quote
Old 10-03-2007, 08:30 PM   #7
Supporting Member
 
cfg83's Avatar
 
Join Date: Sep 2006
Posts: 1,779
Country: United States
2TonJellyBean -

Quote:
Originally Posted by 2TonJellyBean View Post
I trust everyone's judgment and appreciate your responses but are there any good links that you know of?
Sorry to say I don't have a good link either . What does your SG-II say when you are coasting? If MPG goes to 9999, then it is *very* likely that your ECU/PCM is turning off the injectors. When I was in Europe, I saw this behavior with the (stickshift) Diesel I was driving.

From my POV, this is a drivetrain specific question. Different cars operate differently. If you drove a Saturn, I would mooch diamondlarry for what his FSM (service manual) says.

CarloSW2
__________________
Old School SW2 EPA ... New School Civic EPA :

What's your EPA MPG? http://www.fueleconomy.gov/feg/calculatorSelectYear.jsp
cfg83 is offline   Reply With Quote
Old 10-03-2007, 08:35 PM   #8
Registered Member
 
omgwtfbyobbq's Avatar
 
Join Date: Jul 2006
Posts: 1,516
Country: United States
Oh yeah. When coasting most will inject/essentially idle in gear only if the engine speed is below a certain point called DFCO. This point depends on coolant temperature, RPM and the throttle position IIRC, but it's over a fixed range. Even if it isn't idling in gear, the car may send a bit of gas through to keep the catalytic converter warmed up, but it isn't a whole lot.

Edit- Too slow!
__________________
Quote:
Originally Posted by FormulaTwo
I think if i could get that type of FE i would have no problem driving a dildo shaped car.
omgwtfbyobbq is offline   Reply With Quote
Old 10-03-2007, 09:38 PM   #9
Registered Member
 
Join Date: Aug 2007
Posts: 313
Country: United States
With my vehicle it comes down to either losing speed quickly but not burning fuel during the DFCO phase, or coasting longer and keeping the inertia/speed but having to keep the engine at idle using 1/3 GPH. Neutral "seems" far far more efficient. I've seen nothing in the way of any studies that can empirically back this up. Sorry if I'm dense on this guys...

cf, you could check your SG and see if it goes to open loop on decel. If it does that's proof the DFCO is taking place.
__________________
2TonJellyBean is offline   Reply With Quote
Old 10-03-2007, 09:55 PM   #10
Supporting Member
 
cfg83's Avatar
 
Join Date: Sep 2006
Posts: 1,779
Country: United States
2TonJellyBean -

Quote:
Originally Posted by 2TonJellyBean View Post
With my vehicle it comes down to either losing speed quickly but not burning fuel during the DFCO phase, or coasting longer and keeping the inertia/speed but having to keep the engine at idle using 1/3 GPH. Neutral "seems" far far more efficient. I've seen nothing in the way of any studies that can empirically back this up. Sorry if I'm dense on this guys...

cf, you could check your SG and see if it goes to open loop on decel. If it does that's proof the DFCO is taking place.
Ok, I will do that tonight and give you an update.

I'd never heard of DFCO until now :

DFCO = Deceleration Fuel Cutoff

Maybe we should add it to the FAQ :

GS FAQ/Glossary, Busted/Confirmed Mods, Archive
http://www.gassavers.org/showthread.php?t=1088

My overall POV on this is that each has it's place in hypermiling. If the car features DFCO, then this can be used as a tactic for increasing MPG when you need to slow down because of traffic. If you're going to lose all that precious speed, you might as well turn off those injectors.

CarloSW2
__________________

__________________
Old School SW2 EPA ... New School Civic EPA :

What's your EPA MPG? http://www.fueleconomy.gov/feg/calculatorSelectYear.jsp
cfg83 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Two stroke oil in diesel Eybrows General Fuel Topics 16 01-27-2013 09:20 PM
Fuelly Moving to New Servers pb Fuelly Web Support and Community News 4 11-30-2011 10:31 PM
More SMS Requests zbret Fuelly Web Support and Community News 16 02-03-2011 01:09 AM
Switchable power steering idea dieselbenz Introduce Yourself - New member Welcome 11 03-08-2007 05:58 PM
Parking Brakes and Fuel Economy? Matt Timion Automotive News, Articles and Products 0 10-03-2005 02:23 PM

Powered by vBadvanced CMPS v3.2.3


All times are GMT -8. The time now is 10:36 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.