Using DFCO to increase your MPG

[Pavel Olavich]

Originally Posted by adamschneider

I drove over the mountains twice last week and experimented with engine braking quite a bit on the downhills. (I have an automatic transmission.) I was experiencing the same thing that AustinYaris mentioned a few months back: with the exception of a few really steep hills, downshifting to 3rd slowed me down way too much, so I was having to put it in neutral to pick up speed again. As I understand it, DFCO doesn't kick in at all when you're in 4th ("D") in an AT, correct?

So, basically, when going down hills, I was in 3rd gear on the steep parts (which had the dual effects of activating DFCO and slowing down the car so as not to get out of control!), then I would bypass 4th and go into neutral for the shallower inclines. I didn't use D unless I needed to give it some gas. Does this sound like the best way to do it?


EDIT: I just saw Pavel Olavich's most recent post. Pavel, are you saying that the Yaris AT does go into DFCO mode even in 4th gear?

I believe that keeping the shifter in D can activate DFCO if you allow the tranny to automatically downshift, caused by the "grade logic" of the tranny....in this way, your shifter is in D, yet the tranny is in 3rd, and DFCO can happen, given the right circumstances of course. When I find myself driving down steep hills, I tap the brake a tad, and this often causes the tranny to automatically downshift, and I think when it does this DFCO is happening....but my car does not necessarily lose speed...it often just holds the speed constant, and this is often what one wants in these circumstances.

[adamschneider]

Originally Posted by Pavel Olavich

I believe that keeping the shifter in D can activate DFCO if you allow the tranny to automatically downshift, caused by the "grade logic" of the tranny....in this way, your shifter is in D, yet the tranny is in 3rd, and DFCO can happen, given the right circumstances of course. When I find myself driving down steep hills, I tap the brake a tad, and this often causes the tranny to automatically downshift, and I think when it does this DFCO is happening...

I just experienced this yesterday without even trying to: I was headed down off Mt. Hood, tapped the brake, and it definitely downshifted. The question now is whether this causes the fuel to be cut off.

By the way, how did people even learn about DFCO? A google search only turns up results on this forum, the cleanmpg.com forums, and a few others!

[Pavel Olavich]

http://books.google.com/books?id=2MM...ZrhQQ4#PPP1,M1

[BailOut]

Originally Posted by adamschneider

By the way, how did people even learn about DFCO? A google search only turns up results on this forum, the cleanmpg.com forums, and a few others!

I can't claim credit for "discovering" DFCO as there are a lot of ECU/ECM programmers around the world that know about it even better than I do, but I never heard of it until I saw a post somewhere about someone rigging up a switch for their fuel injectors. I ran a search on something like "cutting fuel injector flow" and found the document that Pavel linked earlier: http://www.autoshop101.com/forms/h43.pdf

There's a section in that white paper titled "Deceleration Fuel Cut", and I latched onto it. I thought up a way to test for the presence of DFCO (covered in the first post of this thread) and confirmed it on the 2007 Yaris with the 1NZ-FE engine (I had quite the pucker factor on that first test... hehe).

Once I did that I posted it on CleanMPG and two of the folks there hooked up an indicator light on their fuel injectors (a 2002 Elantra and a 2004 Honda Civic) and verified that the injectors lost all power in a DFCO state. A 3rd person with an older vehicle (I can't remember what model, but it was a 1994) tried the same thing and found his injectors stayed on full-time.

I then spent some time figuring out how to trigger it and how to make it stop, and once all that was done I wrote it up here.

So, while I can't at all claim that I "discovered" DFCO I may be the first "Joe Six Pack" that tested it, confirmed it, found a way to turn it into a purposeful FE booster and then went public with it.