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Old 01-01-2010, 03:21 PM   #127
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Brian- then what is the noise the engine/transmission/something makes when I begin to brake at about 45mph down a hill? And the car stays at about 40mph?
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Old 01-01-2010, 03:25 PM   #128
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Brian- then what is the noise the engine/transmission/something makes when I begin to brake at about 45mph down a hill? And the car stays at about 40mph?
DFCO doesn't make a noise, it just sounds like the engine revving from a downshift.

I'm not sure what the buzzing you are talking about is.
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Old 01-01-2010, 04:56 PM   #129
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DFCO doesn't make a noise, and it doesn't rev the engine or downshift an automatic transmission. There's just a sudden slight deceleration as the idle fuel is cut off. You have to be paying close attention to feel it.

There is a separate function in the ECU that downshifts the transmission if you're coasting downhill and apply the brakes. It increases the "engine braking" so you don't have to use the brakes as much. Touch the gas pedal and let it off, and it'll upshift to high gear and let you pick up speed coasting.
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Old 01-02-2010, 09:58 AM   #130
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Ah you're right, it must be the engine braking. is that bad for gas mileage?
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Old 01-20-2010, 07:16 PM   #131
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I still don't understand DFCO.. if it's seamless and you don't have to do anything, then how do you do what you said in the instructions?

"As soon as you hit an exit ramp off of the highway go into DFCO all the way to the end of the ramp." By doing what? Driving like you would normally?
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Old 01-21-2010, 05:12 PM   #132
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Exactly. Lift your foot off of the gas.
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Old 01-21-2010, 05:19 PM   #133
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I still don't understand DFCO.. if it's seamless and you don't have to do anything, then how do you do what you said in the instructions?

"As soon as you hit an exit ramp off of the highway go into DFCO all the way to the end of the ramp." By doing what? Driving like you would normally?
yes it just means take foot off gas, so that


if the conditions are correct for DFCO, it will kick in.

it will not kick in if
you shift to neutral
or
have any gas pedal input

it really doesn't matter a ton for real world, single use... other than reduce emissions a little bit, and improve mileage a very little bit.

but over the life of the car x how many cars have DFCO, it matters a lot...the end user doesn't need to know
squat about it, it is computer controlled.


the end user can induce DFCO conditions more often than 'natural driving' would
by adjusting how they use the kinetic energy of the vehicle, and the gas pedal and gear choices.
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Old 01-22-2010, 12:10 PM   #134
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it can improve gas mileage a lot if you plan to use it.
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Old 01-22-2010, 02:52 PM   #135
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Keeping your foot off the gas usually does.
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Old 02-25-2010, 08:48 AM   #136
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I just read ecomodder 100+ Tips for better fuel efficiency and I saw this:

Quote:
Originally Posted by ecomodder.com
Braking tips ...

44) The most efficient way to slow down

When you *have* to slow down, here's an approximate heirarchy of methods, from best to worst.

1) coasting in neutral, engine off (ie. roll to a stop);
2) coasting in neutral, engine idling;
3) regenerative coasting (hybrid vehicles)
4) regenerative braking (hybrid vehicles)
5) coasting in "deceleration fuel cut-off" mode (in gear, above a certain engine RPM)
6) conventional friction braking (non-hybrid or hybrid)

Choosing the right method depends on traffic conditions (following vehicles) and how quickly you need to stop.
REALLY?! Is it really more efficient to coast in neutral, with engine idling than using DFCO?! I thought DFCO cuts the fuel and it is better way to slow down...
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Old 02-25-2010, 10:28 AM   #137
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REALLY?! Is it really more efficient to coast in neutral, with engine idling than using DFCO?! I thought DFCO cuts the fuel and it is better way to slow down...
Hello Falconia,

There are times and places for both techniques. If you only have a short distance to worry about, or you are going downhill, or you know you are likely going to stop then DFCO is best as it allows you to decelerate without fuel usage.

But if you would rather maintain more of your speed over a longer distance then coasting in neutral is better as it takes much less fuel to idle for a short while than it does to re-accelerate from a major momentum loss.
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Old 03-03-2010, 01:09 AM   #138
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It's a good read, and I'll definitely pay more attention to how the car performs.

BTW, New guy here. Congrats on the sweet community you guys have made and I'm glad to add myself to it, I've already read tons of great tips.
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Old 03-05-2010, 02:43 PM   #139
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So . . . on the MT, avoid downshifting?
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Old 03-05-2010, 04:00 PM   #140
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So . . . on the MT, avoid downshifting?
Downshift when you need to when cruising or accelerating. (like if you don't have enough power to get up a hill in the gear you're in)

Delay downshifting on deceleration to prolong your DFCO coast. (downshifting earlier gives you more engine braking, which you don't want if you're trying to coast as long as possible "for free")
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Old 03-05-2010, 04:09 PM   #141
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Alrighty! Thanks!

Oh, and I'm assuming that my goal is to stay around 2000 rpms, right? I.e., upshift before it gets TOO far beyond that?
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Old 03-05-2010, 04:44 PM   #142
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Alrighty! Thanks!

Oh, and I'm assuming that my goal is to stay around 2000 rpms, right? I.e., upshift before it gets TOO far beyond that?
High RPMs don't hurt much when you're in DFCO. I routinely go a little above 4k RPM while in DFCO in the mountains.
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Old 03-05-2010, 05:12 PM   #143
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Alrighty! Thanks!

Oh, and I'm assuming that my goal is to stay around 2000 rpms, right? I.e., upshift before it gets TOO far beyond that?
If you're upshifting, you're not in DFCO at all because you're accelerating. That's a topic for another thread.

If you're decelerating/coasting in DFCO, simply don't bother to downshift unless your revs get below 1500.

My typical DFCO maneuver is to just stay in 5th to about 2k or so (I don't really look at the tach), and then skip 4th and downshift to 3rd for the majority of a decel. If I can stretch it further (the light ahead of me is red, or traffic isn't moving), I might grab 2nd and try to maintain enough momentum to stay in 2nd and never have to stop or downshift to 1st if I can avoid it.

The short version of that is: Always coast for as long as possible in DFCO, and always try to time your position within traffic to maintain as much momentum as you can and avoid slowing/stopping unnecessarily.
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Old 03-08-2010, 10:31 PM   #144
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DFCO is not some exotic new feature. It's been a standard feature of most FI systems for at least 20 years. Many of the electronic feedback carbs of the 80s had it. What *has* changed is that its implementation has gotten more aggressive over the years. On my carbureted 1988 Chevy Sprint Metro, it doesn't kick in unless the engine is above 2500 rpm (about 56 mph in 5th) whereas, apparently, 1100 rpm is sufficient on the Yaris.

Also, it is not some magic feature that you can "use" to get better fuel economy. It does one simple thing: When conditions require *less* power than that produced by the 0.2 gal/hour that the Yaris engine consumes at idle, it eliminates that tiny bit of consumption. If that power is needed, e.g. to keep the engine idling, or even to maintain your desired speed when descending a hill, then the fuel is duly provided, and should not be considered to be any sort of waste.
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