I'm copying this from a Yaris forum, because it's good information, and our Fits do the same thing. Here is the post over there.

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What is DFCO?

It is an abbreviation for "Deceleration Fuel Cutoff", and the Yaris' engine (1NZ-FE) has it.


How does it work?

When your Yaris is moving forward with zero throttle and is in gear (engine braking) the ECU (your car's computer) cuts off the fuel flow to the injectors. This means you are experiencing forward movement with no fuel cost.


Does this work on both the Liftback and the Sedan?

It is not dependent on body style.


Does this work on both the manual and automatic transmissions (MT and AT)?

Yes, but it is much more efficient with the MT. The MT can achieve DFCO in any gear as long as the clutch is engaged (meaning you don't have it pushed in) and your foot is not touching the throttle. Early versions pf the AT (Including ones sold in the U.S. until around January 2007) can only achieve DFCO with a gear selection lower than (D)rive, i.e. 3 or L, but since half way through the 2007 model year the AT can achieve DFCO in all gears.


Is the Yaris the only car that does this?

Not by any means. Many cars manufactured since 1999, even a few as early as 1995, have this feature.


How can I tell if a vehicle other than the Yaris has DFCO?

Be careful with this test as you may lose Power Steering and Power Brakes during it! Choose the right time and location to perform the test.

On any level or slightly downhill road get up to at least 40 MPH, then start engine braking by keeping the vehicle in gear and letting all the way off the throttle while keeping the clutch disengaged (MT) or keeping the transmission in a gear lower than D (AT). Notice the deceleration force and the sound of the engine.

Now tun off your ignition (This is where you may lose your PS/PB, so be wary!) and watch for any harsher deceleration or change in the pitch of the engine for a few seconds.

If nothing was any different with the ignition turned off then your vehicle uses DFCO. If it decelerated at a different rate or pitch with the ignition off then it does not use DFCO. Do not forget to start your engine back up!


How long does it take the Yaris' 1NZ-FE engine to enter and leave the DFCO mode?

The transition takes between 500 and 750 milliseconds (ms) depending on several other ECU measurements.


What will make the engine leave DFCO mode?

1) Touching the accelerator.
2) Dropping below 1,100 RPM.
3) Putting the transmission in neutral/disengaging the clutch.


Does changing gears make the engine leave and then quickly re-enter DFCO mode?

If you take <= 1 second to change gears (as most experienced drivers do) then no, you will remain in DFCO the entire time. However, if your shift takes longer than 1 second there is a chance you will leave DFCO for a few seconds.


Will the ScanGauge II show a DFCO state in the Yaris?

Due to each manufacturer having proprietary OBD codes for fuel injection the SG II cannot truly show a DFCO state. However, you can verify a DFCO state by correlating several other readings:

1) LOD (Engine Load) will drop well below a reading at idle. My 5MT Yaris shows an LOD of 43 at idle but only 34 in DFCO.
2) GPH/LPH (fuel rate) will bottom out at 0.2 - 0.4 GPH or 0.75 - 1.5 LPH.
3) LP (fuel system loop) will be solidly Open.
4) MPG/LHK will go to the high side (it will take a few seconds but it will go quite high, i.e. 100+ MPG).


How can I use DFCO to increase my MPG?

Let me count the ways...

- When traveling down a grade get into DFCO mode instead of racing from corner to corner or riding your friction brakes, etc.

- As soon as you hit an exit ramp off of the highway go into DFCO all the way to the end of the ramp.

- When approaching a stop or turn use DFCO to decelerate down to just a few MPH before applying the friction brakes.

- When you're stuck in heavy traffic use the well-known technique of finding the right speed to keep a few car lengths of distance ahead of you and maintain forward momentum, then use DFCO to decelerate when needed instead of your friction brakes.

- Use DFCO to maintain controlled forward movement while you're trying to stay moving while approaching a traffic light that you're waiting to turn green.


How can I maximize my speed control when using DFCO?

By selecting the right gear for the purpose. Select a higher gear for faster DFCO movement and a lower gear for slower movement (this is where the MT really outshines the AT). Both transmission types can have their DFCO movement speed adjusted by tapping the fuel when a higher speed is required than gravity can achieve, and by light friction brake usage when some speed needs to be bled off but the next lower gear would be too much.


Does using DFCO hurt my vehicle?

No more than maintaining an idle, or maintaining a fuel-based engine load on it would be, as normally happens in these instances.


Is DFCO more efficient than using the clutch and/or friction brakes to stop?

When you push the clutch in or the AT enters its lowest power state your engine idles (the AT idles a bit higher than the MT in order to produce the pressures needed to operate the torque converter). Idling requires fuel while DFCO does not so DFCO is more efficient. However, you will not be able to use DFCO to completely stop all forward movement as you will eventually drop below 1,100 RPM, so the idea is to use DFCO as much as possible before engaging the friction brake system in the normal manner.


Is using DFCO like this legal?

Absolutely. Even those rare Interstate passes or other roads where engine braking is prohibited don't apply here because those areas have banned engine braking due to emissions controls (notice how semi trucks spew acrid black smoke when they are engine braking), but we are producing zero tailpipe emissions because we are not burning any fuel at all.


What kind of MPG increase will I see by using DFCO?

The answer will vary from person to person, vehicle to vehicle and according to driving conditions but you can rest assured that you will never see an increase in fuel consumption due to using DFCO. Remember that when in the DFCO mode you are using absolutely no fuel.

DFCO is also symbiotic with other high-mileage techniques. For example, ignoring tailgaters when you are doing the speed limit (or the safest speed for the scenario) applies to using DFCO on a downhill grade as much as it does when you're driving using the friction brakes (don't use fuel to speed up just to please a tailgater because they'll still be tailgating you anyway). Another example would be the one I gave above of using DFCO to control your momentum while waiting for a traffic light up ahead to change to green.

Here is one example of the mileage you can achieve in a Yaris without doing anything drastic:

As of this writing my 2007 Yaris Liftback is not quite 3 weeks old yet and will not even hit 1,000 miles until at least next weekend, so I am most definitely within the break-in period. Local temperatures have been 25-40F. My daily commute is over a mountain from 4,500ft. to 8,900ft. and then down to 6,300ft. over a total of 27.2 miles (one way), and I start that climb 1.3 miles after I leave my home. We are still on winter gas (which robs anywhere from 3-10% MPG) and I am running on Mud + Snow tires. In other words I am by no means in an optimal position to achieve high mileage.

The only mod I have made to my Yaris so far is a K&N air filter and I used 2.5oz. of Lucas Fuel Treatment at my second fueling.

My efficiency on that tank was 43.67 MPG.

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Fray's Comments:

The Fit AT DOES go into DFCO as long as the engine speed is above ~1100rpm. I have personally verified this with my recently received ScanGauge.

A lot of people here and on the Yaris forum seem to be concerned that coasting in gear will somehow cause increased wear on engine and transmission components.

I postulate that it will not cause additional wear due to a couple technical factors:

-Load on the engine will likely be less than accelerating at more than a grandmother pace.
-Oil is still circulated in the engine and transmission.


I would also clarify that DFCO is not really a 'feature'. It's a default behavior of the ECU.

 

Good post! I do this as much as possible. The last road I turn onto to get to work has a nice hill in which I let off the throttle completely and can pretty much make it to the stop sign, quite a ways I may add. I have a few stop signs/lights times pretty well so I can let off the gas and make it to the stop only needed to apply the brakes at the last minute.

I saw in another post in here about setting the fuel cut off value? I would think the actual ECU of the car would handle that but maybe I'm wrong?

 

Wrote about this in SG Schooling a few times. It's all part of driving without brakes. If you have a LONG way to glide you better off going to neutral and run at ideal or kill the eng if you are OK with that.
If it's a med coast down from speed leave it in 5th or 4th but your coast or Glide will be way shorter.

With the SG it will show the fuel flow go to zero.

 

Paul, if I'm not mistaken, there's a screen in the SG that displays cutoff and has a number next to it. I think this is able to be changed, I'm a little confused by it? This is in the "settings" if I'm not mistaken.

 

The best way to see it is the Gallons Per Hour gauge. When it goes to 0.00, you know you're not burning any gas.

 

I think I made this confusing. My real question is if there is a value to be set which controls when the actual "cutoff" occurs. For instance, you take your foot off the gas, in gear of course, and watch the SG (GPH) and it will slowly creep down and then the GPH value is 0.00.

Maybe I'm looking too far into this, sorry.

 

That would really depend on whether there is a signal from the ECU that it's going into DFCO. If there was, then there's probably a code associated with it, which you could then program the ScanGauge to look for.

However, I don't feel it's necessary - just use the GPH gauge. When it goes to 0.00, you're in DFCO. I set my ScanGauge Rate to High, and it reacts to lifting off the throttle within a second.

 

Dave, My understanding on the SG cutoff is to make the SG read better when in gray areas of it's calc's and algorithms. I do not think it's altering the Honda ECU at all.

Maybe I have that wrong.

When I called SG about the X gage HP reading going blank on full throttle, I was told I needed to adjust that. I never did, as HP was more of a novelty for me being 99% more interested in best case Eco.

From day on with the SG and the default settings, I was able to observe the fuel shut off when I lifted and let the eng brake the Fit. Pretty sure I mentioned that and there was some discussion on the best way to use that in the schooling thread.Around March???

 

I actually ound a good thread about this over on the cleanmpg forum. Those guys recommended setting the fuel cutoff in the SG 1 value higher than the TPS value is.

 

That's what I've heard too. So, I usually see a TPS reading of 12 without A/C, 13 with A/C on. With that being said, like pcs0snq I've never messed with the default setting and I've seen the DFCO since day one. It may be a little more important in an automatic trans car, but I have a manual and it's fine at the default setting.

 

very nice explanation! After using scan gauge, I started to notice DFCO and used it to my advantage with all of those situations you posted. It sure does help on increasing MPG. So far this is my 3rd tank on my Fit AT (8k miles) with Scan Gauge and it is reporting 37 mpg (it was 38.7 but I was searching for a sushi place for about an hour lol). previous two tanks were about 34-36mpg without using DFCO to my advantage.

 

DFCO is my mother ****ing JAM! save hella gas guys. ive gone from 32-34 to over 40 in my MT fit just by learning how to drive efficiently

 

Evidence of what I've been saying: THE thing that affects your fuel economy the most is


YOU!


Good job!

 

absolutely!!

i listened to a podcast talking about the scangauge. they were saying it's like a bathroom scale. it doesn't actually DO anything. but, if you're USING it, you'll know what to do in order to get results

 

Quote:

How can I use DFCO to increase my MPG?

Let me count the ways...

- When traveling down a grade get into DFCO mode instead of racing from corner to corner or riding your friction brakes, etc.

- As soon as you hit an exit ramp off of the highway go into DFCO all the way to the end of the ramp.

- When approaching a stop or turn use DFCO to decelerate down to just a few MPH before applying the friction brakes.

- When you're stuck in heavy traffic use the well-known technique of finding the right speed to keep a few car lengths of distance ahead of you and maintain forward momentum, then use DFCO to decelerate when needed instead of your friction brakes.

- Use DFCO to maintain controlled forward movement while you're trying to stay moving while approaching a traffic light that you're waiting to turn green.

It was never meant to be a long distance solution, just something to keep in mined that hopefully will add up over time.

 

Anyone have any data or experience to know what shifting the AT in and out of neutral at speed does to the tranny?

For the MT, this is a no brainer. I'd use coasting if I had a long run and DFCO if I need to slow the car down for traffic or a light etc. Obviously, pick the technique that will save you the most gas. I can see a reason to have both in the arsenal.

Are there still laws against being in neutral at speed?

 

Did it saw the SG setting writes to the ECU and changes how the injectors shut off? Perhaps a link to what you saw. Thanks

 

Informative post, but this SHOULD be common knowledge to anyone that understands the fundamentals of modern fuel injection.

It's not anything special, just common sense really. If you've ever had a wideband A/F gauge, or even a narrowband light show gauge, or a scangauge, it makes itself very apparent.

I article is WRONG when it says, "Many cars manufactured since 1999, even a few as early as 1995, have this feature."

My 89' CRX cut the fuel injectors coasting in gear, as does my buddies 88' Conquest. Both with OBD0 Ecu's.

It's not a "feature" per say, it's a function. The article, the way it's put together, makes this seem like a super secret fuel saving feature that was just thought of in the last 10 years. It's not.

Here's a page from a Honda PGMFI training manual.



Pretty much ALL fuel injection operates the same way. There all small variances between manufacturers (such as the rpm where the injectors resume), but the fundamentals remain.

Also in regards to fuel savings, it's best to decelerate in gear when you're going to eventually stop. Let off the gas early and let the engine slow the car before braking.

A lot of hypermilers will coast in neutral on a long flat stretch with a tailwind or down a hill. You will coast farther and use less gas than you would coasting in gear, but having to accelerate sooner.

 

The absolute best for Eco is time your stops, looking far ahead and coast in neutral with engine off.
That's the best you do short of walking.

All else is a comprise, but sometimes necessary

 

You're being ignorant.

Using DFCO is a good trick when you know you are going to slow to a stop, say, a traffic light ahead turning red.

What YOU did, sure, works for getting a VERY long distance without applying power. In commuting, you're probably not going to be able to do that very often. You SHOULD however be able to lift off the throttle when coming to a light, where the drag of the engine in DFCO is a GOOD thing.

So, basically different situation, but NEITHER is a load of bull. Use them in different situations, that's all.