Using DFCO to increase your MPG

[tim584]

Hi all
i want to know if the 2NZ FE engine is equiped with DFCO? (1.3 VVTi engine, like european yaris)
Thanks

[BailOut]

tim584,

Please run the test outlined in the first post in this thread in order to determine if your vehicle has it or not. It should, but there's only one way to verify.

[tim584]

Yes iknow that, but can i damage my engine when i do the test?

[Pavel Olavich]

For auto transmissions, here is what you can do to get into DFCO mode:

When going down an incline, tap your brake lightly. This will cause the "grade logic" in the auto tranny to down shift a gear automatically, something that Honda pioneered years ago. Then you will find that the car experiences some resistence as you glide down the hill. The rpm's will increase, and if you have a scan gauge, the GPH value will often be 0.3 or 0.2. I suspect the car is in DFCO, as the MPG is 200+. I think the ScanGauge will never post less then 0.2 GPH, so even though your car is in DFCO, the GPH shows 0.2. I could be wrong on this, and also, the auto will not necessarily run the "Grade Logic" routine unless the conditions are ripe, in regard to incline, speed, acceleration, that sort of thing. I think that working with "grade logic" is better and safer then placing the auto in nuetral. I suspect long term tranny damage to do the nuetral thing. It is my guess that if the auto Yaris in fact has DFCO, then after it enters DFCO mode, it will pop back out at the point that the movement of the car no longer is able to pressure-turn the engine (via the transmission).

If DFCO works as I think it does, then it is far better then placing the auto in neutral, because keeping the car in D with grade logic auto downshifts will (1) maintain your speed, using the compression of the motor (2) allow you to drive your auto as intended, and probably eliminate damage from neutral coasting (3) DFCO mode turns off the injectors...while coasting in neutral does not, as the idle feed of gas is still maintained.

Oh before I forget, BailOut: Nice write up, but you have the "disengage" and "engage" terms mixed up....a manual transmission is engaged when the clutch pedel is out, and DIS-engaged when the clutch pedel is pushed in...but your point is not lost to us. ;-)

[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?

[joe keeney]

Its called hyper driveing.

[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.

[Pavel Olavich]

Honda uses the term "Grade Logic"....what does Toyota call their's? Anyone know?

[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.

[steved]

Maybe someone in this forum could hook up an indicator light on there Yaris to see if the injectors really do cut off. (especially an automatic)

This way there would be 100% proof that DFCO really works on our cars.

I would do it, but someone living in an mountain area would be better at testing this. ( and I'm useless in electronics and wiring)

[ECHOKnight2000]

Originally Posted by Pavel Olavich

Honda uses the term "Grade Logic"....what does Toyota call their's? Anyone know?

I think Toyota referrs to it as uphill/down hill shift logic. For automatics at least. The engine won't gear hunt as much going down hill or up hill (granted if you're gradually going up a hill. I don't know if that has to do with what we're talking about but I bet it has some relation as far as DFCO.

I don't have a Yaris but the ECHO (auto) has a similar set up obviously not the up to date version like the Yaris. I have one question though. I have a scanguage II and I have one of the read outs on closed or open loop. The fuel loop or whatever...anyway I read that when the loop is open it actually means the ECU cuts off fuel to the engine to save gas...so like when I cruise from about 55 and up and just let the car go even in drive the loop opens for a bit until I get to a certain speed. It really opens up either when I floor it or downshift to a lower gear like coming off the highway. I was wonder if this is DFCO cause it cuts off fuel or at least I think it does. Can anyone help me on this who knows about cars? Thanks!

[Pavel Olavich]

Originally Posted by ECHOKnight2000

I think Toyota referrs to it as uphill/down hill shift logic. For automatics at least. The engine won't gear hunt as much going down hill or up hill (granted if you're gradually going up a hill. I don't know if that has to do with what we're talking about but I bet it has some relation as far as DFCO.

I don't have a Yaris but the ECHO (auto) has a similar set up obviously not the up to date version like the Yaris. I have one question though. I have a scanguage II and I have one of the read outs on closed or open loop. The fuel loop or whatever...anyway I read that when the loop is open it actually means the ECU cuts off fuel to the engine to save gas...so like when I cruise from about 55 and up and just let the car go even in drive the loop opens for a bit until I get to a certain speed. It really opens up either when I floor it or downshift to a lower gear like coming off the highway. I was wonder if this is DFCO cause it cuts off fuel or at least I think it does. Can anyone help me on this who knows about cars? Thanks!

I think DFCO and Grade-Logic are two completely different processes, and are not related, although this is not to say that they don't cooperate together.

As for open/closed loop, when open, the ECU uses "maps" for determining ignition, and other stuff. When the loop is closed, the ECU uses realtime calculations to control everything.....I could be wrong, so maybe someone has a much better explanation, as my sources are a bit flakey on this. I write this because I don't want to spread info if I'm not 100% sure about.

[songa]

i know this is an old thread but still very important and relevant...and im also sorry for not having read the entire thread yet as i am in a bit of a hurry so im sure im missing some details but i have one quick question..

DFCO is great, but say you are coasting downhill and you want to pick up as much speed/momentum as possible so you can continue coasting once the road levels off a bit. if you stay in DFCO, you will feel that it is holding your car back a bit, aka "engine braking." this scenario is only good because the DFCO is cutting off fuel. However, because of the DFCO you are not taking full advantage of gravity from the downhill slope and are therefore losing out on some added speed/momentum that you would get if you were to coast in neutral instead. this is a trade off...an opportunity cost issue. does this make sense?

so to my logic, if you really need that extra speed and momentum that you would get from gravity going downhill, neutral coasting is more beneficial. you use minimal fuel for a much faster speed and larger momentum that you will benefit from once the road levels off. this way, you can take advantage of much longer distances for a lil bit of fuel.

if you dont need the extra speed and momentum, DFCO would be more fuel efficient because you are not using any fuel at all. however after the downhill, you may not be able to coast much longer as you have limited your speed to an extent. this means you can coast for a shorter distance than the neutral coasting method, but you will be doing it at no fuel cost at all.

does this make sense?

[Sodium Duck]

DFCO is just ONE driving tool. Like all fuel saving tools and techniques, is to be used in certain situations -- not all. Your point has bassically already been discussed before.

To be a hypermiler, you use a combination of all different driving techniques and styles to attain a maximum MPG. Sometimes you use DFCO on one hill, and shift into neutral on another. Or whatever else it is that you do.

[Bullet120]

DFCO down hill, gain some speed, use no fuel at all.

Neutral down hill, with car on, gain a little more speed and burn fuel otherwise not burned.

Hmm, no fuel, or some fuel. Which sounds more efficient?

Not to mention neutral coasting and autos don't like each other. However, ICE off neutral coasting in a MT is very efficient.

[voodoo22]

Originally Posted by Bullet120

DFCO down hill, gain some speed, use no fuel at all.

Neutral down hill, with car on, gain a little more speed and burn fuel otherwise not burned.

Hmm, no fuel, or some fuel. Which sounds more efficient?

Not to mention neutral coasting and autos don't like each other. However, ICE off neutral coasting in a MT is very efficient.

Like Sodium Duck says, it's a combination of techniques based on your situation. In situations where you don't want to slow down, but the decline is not steep enough to allow you to use DFCO without losing speed. That's when you want to use N.

You are also wrong about coasting in N in an auto. Most newer autos have no problems and incur no damage from doing this. You don't need to rev match or anything.

It really doesn't matter how efficient a maneuver is with a MT when you're driving an AT. Most AT's cannot ICE off coast without incurring damage, but some can. For the masses who can't N-ICE on coasting is their best choice when DFCO isn't suitable.