Go Back   EcoModder Forum > EcoModding > Hypermiling / EcoDriver's Ed
Register Now
 Register Now
 

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 07-04-2012, 04:11 AM   #1 (permalink)
Ecomuggler
 
Xist's Avatar
 
Join Date: Jun 2012
Location: Mesa, AZ
Posts: 4,783

Chorizo - '00 Honda Civic HX, baby! :D
90 day: 44.29 mpg (US)

Mid-Life Crisis Fighter - '99 Honda Accord LX
90 day: 35.16 mpg (US)
Thanks: 2,723
Thanked 812 Times in 610 Posts
Deceleration Fuel Cutoff (DFCO) (originally implemented for emissions, not mileage)

I just heard of this, so learning that it was implemented fifteen years ago is slightly embarrassing. I read a few times that it has pretty much been on all vehicles since OB II came out in 1996. Some guy wrote that he thought that DFCO was required by OB II, so I looked into it, and found:

Therefore Deceleration fuel cconditions cutoff (DFCO) is sued to utoff control catalyst temperature during vehicle coastdown, when the engine intake manifold pressure is drive too low to a, allow llow complete combustion. To prevent unburned fuel from entering the converter, the fuel injectors are shut off by the engine controller.

So, DFCO was implemented for emissions, not mileage?

  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 07-04-2012, 07:10 AM   #2 (permalink)
Master EcoModder
 
Join Date: Sep 2009
Posts: 5,927
Thanks: 877
Thanked 2,014 Times in 1,300 Posts
I know for a fact is was in the 1981 Datsun Z cars. Might have gone back to 76 but not absolutely sure. DFCO allowed the elimination of air injection into the exhaust system. They may have tried it on some of the last carburetors. Electronically shutting off the idle circuit, but that is speculation.

Easy test is to place a stethoscope on an injector and rev the engine, let the throttle go completely back to idle and the injectors will stop ticking completely until the RPM drops to just above idle speed. That may not work in some of the more modern versions but it worked in a 1981 Z car long before OBD 1 or 2.

regards
Mech
  Reply With Quote
Old 07-04-2012, 12:12 PM   #3 (permalink)
(:
 
Frank Lee's Avatar
 
Join Date: Jan 2008
Location: up north
Posts: 11,859

Blue - '93 Ford Tempo
Last 3: 27.29 mpg (US)

ShWing! - '82 honda gold wing Interstate
90 day: 33.65 mpg (US)

F150 - '94 Ford F150 XLT 4x4
90 day: 18.5 mpg (US)

Sport Coupe - '92 Ford Tempo GL
Last 3: 69.62 mpg (US)

Moon Unit - '98 Mercury Sable LX Wagon
90 day: 21.24 mpg (US)
Thanks: 1,334
Thanked 2,820 Times in 1,800 Posts
The old carbed VWs (don't remember what year it started- '71?) had a vac diaphragm added to the throttle so that it would gently close on decel instead of snapping shut, to reduce emissions.
__________________


  Reply With Quote
Old 07-04-2012, 07:11 PM   #4 (permalink)
Aero Wannabe
 
COcyclist's Avatar
 
Join Date: Dec 2007
Location: NW Colo
Posts: 514

TDi - '04 VW Golf
TEAM VW AUDI Group
90 day: 53.45 mpg (US)
Thanks: 300
Thanked 91 Times in 75 Posts
Quote:
Originally Posted by Xist View Post
Therefore Deceleration fuel cconditions cutoff (DFCO) is sued to utoff control catalyst temperature during vehicle coastdown, when the engine intake manifold pressure is drive too low to a, allow llow complete combustion. To prevent unburned fuel from entering the converter, the fuel injectors are shut off by the engine controller.

So, DFCO was implemented for emissions, not mileage?
Nice find! Thanks for posting this. Care to share your source?
__________________
60 mpg hwy highest, 55+mpg lifetime
TDi=fast frugal fun
make NOx not Carbon

  Reply With Quote
Old 07-04-2012, 07:21 PM   #5 (permalink)
one of thOOOse people
 
Join Date: Mar 2009
Location: the cloud(s)
Posts: 258

twitchy - '98 honda civic dx + sir + ls
90 day: 30.2 mpg (US)
Thanks: 0
Thanked 67 Times in 53 Posts
My dad's 84 Nissan Sentra was carborated and would cut fuel flow when coasting. However my 98 Honda Civic is injected and has OBD2 and does not cut off fuel when coasting. I have heard that some cars do not cut fuel because there is an increase in emissions as the fuel come back on.
  Reply With Quote
Old 07-04-2012, 08:18 PM   #6 (permalink)
MPGuino Supporter
 
t vago's Avatar
 
Join Date: Oct 2010
Location: Cedar Rapids, IA
Posts: 1,723

The Karen-Mobile - '05 Dodge Magnum SXT
Team Dodge
90 day: 25.56 mpg (US)

Fiat Dakota - '00 Dodge Dakota SLT RWD Quad Cab
90 day: 16.67 mpg (US)

The Red Sled - '01 Dodge Durango SLT 4WD
90 day: 16.96 mpg (US)
Thanks: 763
Thanked 654 Times in 418 Posts
When I changed the chassis wiring harness in the engine bay of my truck, I used a Dremel tool with a wire wheel to clean all of the chassis ground posts, all of the grounding nut surfaces, and all of the ground loop connectors on the harness. After that, I coated all of the exposed metal with dielectric goop, then put them back together.

The net result was (other than to get rid of a really annoying intermittent condition whereby my transmission would just decide to go into limp-in mode for 5 seconds while at speed - with no codes, of course) that my truck now tends to go into DFCO a lot more easily than before. There are sections of my commute where the truck will actually do DFCO regularly, whereas before it never did.

I'm tending to lean toward "DFCO = fuel savings," myself.
__________________
The Fiat Dakota


The Karen-mobile


The Red Sled
  Reply With Quote
Old 07-04-2012, 09:12 PM   #7 (permalink)
Master EcoModder
 
Join Date: Sep 2009
Posts: 5,927
Thanks: 877
Thanked 2,014 Times in 1,300 Posts
The problem dates back a long time. When you close the throttle butterfly on an engine that is running at high RPM the manifold vacuum can approach the close to perfect vacuum of outer space. Under those conditions combustion is impossible and unburned hydrocarbons go ballistic.

Even my 37 Ford had a small spring loaded valve in the butterfly so when you got that super high vacuum, some air would flow through the engine. It also had the intake manifold heated by exhaust gas through a passageway that was right under the carburetor, which rotted out a lot of the aluminum manifolds long ago, on an engine that still had a hole in the grille and radiator for a manual crank option.

In the late 60s air injection became practically mandatory, where air was pumped into the exhaust to help with burning the fuel more completely. This was the era of air injection lines into the exhaust manifold.

Later when catalytic converters became mandatory, manufacturers eventually went with fuel injection which allowed for more precise control of fuel delivery. When they realised that they could just shut the injectors off when the vehicle was decelerating while still in gear, then they could eliminate the additional complexity of air injection systems.

In the transitional period from carburetors to FI the manufacturers tried a lot of different "solutions" with carburetors. I think Toyota was one of the last to finally go over completely to FI.

By the time 3 way catalysts were universal, FI was essential to preserve the cats.

It's interesting to see what developments are coming with the availabliity of massive memory and super fast computer calculations. Multiple injections directly into the cylinder while combustion is underway allow ultra high compression with regular fuel. Spark knock is impossible. A long road from the DB 601 engine in the German Me 109 of the mid 1930s with direct injection. You have to see the humor in the "new" direct injection that dates back almost 80 years in aircraft, possibly even longer in other applications.

DFCO was one of the first "advancements" that became possible with computer controls. Nissan went with an EFI system, licensed from Bosch in 1975. It was simultaneous injection, not sequential. They did not need any catalytic converter, EGR, or air injection in the 1975 Federal versions of the first 280 Z. I believe this had DFCO but I can't be absolutely sure. My 76 280 had a N47 early EFI head, on a factory new 83 short block with flat top pistons. This raised the compression from 8.5 to 1 to almost 10 to 1. 160 PSI to 190 PSI on a compression gauge.

It required the base timing to be dropped from 10 to 7 degrees and premium fuel only. With the .75 overdrive 5th gear and the stock 3.54 rear axle 3k RPM was good for right at 85 MPH and at 65, she would push close to 30 MPG highway, with a Motorsports aero kit and lexan headlight covers.

regards
Mech
  Reply With Quote
The Following 5 Users Say Thank You to user removed For This Useful Post:
Ang84Indy (07-04-2012), niky (08-23-2016), redpoint5 (07-07-2012), TEiN (07-07-2012), Xist (07-04-2012)
Old 07-04-2012, 11:11 PM   #8 (permalink)
Ecomuggler
 
Xist's Avatar
 
Join Date: Jun 2012
Location: Mesa, AZ
Posts: 4,783

Chorizo - '00 Honda Civic HX, baby! :D
90 day: 44.29 mpg (US)

Mid-Life Crisis Fighter - '99 Honda Accord LX
90 day: 35.16 mpg (US)
Thanks: 2,723
Thanked 812 Times in 610 Posts
Wow, Old Mechanic, that was some great information! Thanks for sharing it with us!

Quote:
Originally Posted by COcyclist View Post
Nice find! Thanks for posting this. Care to share your source?
Wow, I use references when talking to my girlfriend! How did I quote something without providing the reference?! Some college graduate I am!

http://groups.engin.umd.umich.edu/vi...ganesan_w2.pdf

I think that this was part of a college course. Google just pointed me to the .pdf

I read some of it and then just searched for DFCO. That is some heavy information!
  Reply With Quote
Old 08-23-2016, 12:50 AM   #9 (permalink)
EcoModding Lurker
 
Join Date: Aug 2016
Location: Sri Lanka
Posts: 1
Thanks: 0
Thanked 0 Times in 0 Posts
So do carbureted engines from 1980's to 1990's waste petrol/gasoline when engine brake/ downshifting? Take the lancer 2nd generation for example, does it have a valve that shutts off fuel from the carb to the engine? Or tldoes the engine forcefully suck in fuel to the engine and waste it. Also does it mean that we should coast to neutral when stopping? Thanks alot.
  Reply With Quote
Old 08-23-2016, 07:17 AM   #10 (permalink)
Master EcoModder
 
oldtamiyaphile's Avatar
 
Join Date: May 2009
Location: Australia
Posts: 1,101

UFI - '12 Fiat 500 Twinair
Team Turbocharged!
90 day: 49.6 mpg (US)

Jeep - '05 Jeep Wrangler Renegade
90 day: 18.09 mpg (US)

R32 - '89 Nissan Skyline

STiG - '16 Renault Trafic 140dCi Energy
90 day: 32.81 mpg (US)

Prius - '05 Toyota Prius
Team Toyota
90 day: 50.25 mpg (US)

Premodded - '49 Ford Freighter
90 day: 13.48 mpg (US)

F-117 - '10 Proton Arena GLSi
Pickups
Mitsubishi
90 day: 35.01 mpg (US)
Thanks: 236
Thanked 245 Times in 187 Posts
Quote:
Originally Posted by ruwantha456@gmail.com View Post
So do carbureted engines from 1980's to 1990's waste petrol/gasoline when engine brake/ downshifting? Take the lancer 2nd generation for example, does it have a valve that shutts off fuel from the carb to the engine? Or tldoes the engine forcefully suck in fuel to the engine and waste it. Also does it mean that we should coast to neutral when stopping? Thanks alot.
Yes, carb'd engines should be in neutral (engine on or off) when coasting.

__________________






  Reply With Quote
Reply  Post New Thread


Thread Tools




Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com