My idea about DFCO. - Toyota Yaris Forums

Sodium Duck · 02-03-2009, 07:36 PM

Why can't hitting the brakes activate DFCO or something similar to it?

I'm obviously not a mechanic, or knowledgeable about engines - is there a safety issue related to this, or would the engine just stall?

*curious*

Loren · 02-03-2009, 08:01 PM

Generally speaking, most people have already taken their foot off of the gas before they start braking. (because if they've been trained properly, they are using the same foot for the gas and the brake)

DFCO activates anytime you are off-throttle, in gear and the momentum of the car is sufficient to keep the engine turning at more than about 1200 rpm.

Given those two facts... is there any need to involve the brakes in the equation? If you're driving an automatic, DFCO is already activated even BEFORE you start braking, and will stay that way until the engine revs decrease to the point that the engine needs fuel to idle. With a manual, the same holds true until you put the clutch in, then the engine has to exit DFCO mode to idle.

smacky · 02-03-2009, 08:07 PM

From what I've observed DFCO will work until your braking reduces your speed and your RPMs get to 1000ish. Braking for a short time (around a second) will also shift you into the next gear down and that way you can keep your RPMs a little higher and DFCO will stay on a little longer.

twowheels · 02-03-2009, 08:11 PM

Quote:

Originally Posted by smacky

From what I've observed DFCO will work until your braking reduces your speed and your RPMs get to 1000ish. Braking for a short time (around a second) will also shift you into the next gear down and that way you can keep your RPMs a little higher and DFCO will stay on a little longer.

I've been wondering on the manual whether downshifting would help bump the RPMs up a bit to keep it in DFCO mode longer, but since I don't have a tach (

) I can't really tell. Anybody with a tach and the stock 15" wheels have any idea what speed 1000 RPM is in each gear?

Besides, I don't like using my expensive clutch to slow down, so I probably wouldn't do it anyhow.

Altitude · 02-03-2009, 08:30 PM

Quote:

Originally Posted by twowheels

Besides, I don't like using my expensive clutch to slow down, so I probably wouldn't do it anyhow.

This comment puzzles me.

MadMax · 02-03-2009, 09:50 PM

So, does it make sense to downshift the automatic to keep engine decelerating occurring as long as possible? I've gone down as far as second gear on my auto a few times; but I've often wondered, is it putting increased wear and tear on my transmission just to save a few drops of gas?

I gotta admit, this DFCO feature intrigues me and I am trying to maximize its use!

Cheers! M2

Loren · 02-03-2009, 11:08 PM

Unless I'm hardcore hypermiling, I don't bother downshifting below 3rd gear on a DFCO coast-down. You can go pretty darned slow in 3rd gear before getting below 1000-1200 rpm.

With an automatic, the transmission will automatically downshift as you decelerate and should keep your revs up until you're at a near stop, anyway.

twowheels · 02-04-2009, 12:35 AM

Quote:

Originally Posted by PK198105

the clutch doesn't slow the car, the engine's compression slows it down. the wear and tear on the clutch happens when you let it out after switching gears

I realized that, but it was a shorthand way of saying that I don't want to wear out the clutch rather than the much cheaper brakes....

Sodium Duck · 02-04-2009, 11:00 AM

I thought that DFCO turns off when you hit the brakes? I remember reading that somewhere on the forums.

eTiMaGo · 02-04-2009, 11:03 AM

nope, it only turns off when you hit the gas, or the engine gets below a certain speed

Sodium Duck · 02-04-2009, 12:56 PM

My idea has become a reality. =]

MadMax · 02-04-2009, 01:12 PM

Quote:

Originally Posted by Loren

Unless I'm hardcore hypermiling, I don't bother downshifting below 3rd gear on a DFCO coast-down. You can go pretty darned slow in 3rd gear before getting below 1000-1200 rpm.

With an automatic, the transmission will automatically downshift as you decelerate and should keep your revs up until you're at a near stop, anyway.

I thought someone with a ScanGauage and an auto said it takes a bit for the transmission to downshift after you let off the gas; hence my manually downshifting to kick the DFCO in sooner. If that is not correct, and all I need to do is let off of the gas, I would like to know...

Cheers! M2

ddongbap · 02-05-2009, 08:11 PM

Quote:

Originally Posted by Sodium Duck

My idea has become a reality. =]

Grats.

CKaelin · 02-06-2009, 12:54 PM

Quote:

Originally Posted by twowheels

Besides, I don't like using my expensive clutch to slow down, so I probably wouldn't do it anyhow.

I had 230,000 miles on the original clutch in my old 97 tacoma and I downshifted all the time!

02-03-2009, 07:36 PM	#1
Sodium Duck ╚══════════RN Drives: 2008 Liftback Join Date: Oct 2008 Location: Western Mass. Posts: 999	My idea about DFCO. Why can't hitting the brakes activate DFCO or something similar to it? I'm obviously not a mechanic, or knowledgeable about engines - is there a safety issue related to this, or would the engine just stall? curious __________________ 42.88

02-03-2009, 08:01 PM	#2
Loren What? Drives: 2007 Yaris LB Join Date: Nov 2008 Location: Safety Harbor, FL Posts: 1,006	Generally speaking, most people have already taken their foot off of the gas before they start braking. (because if they've been trained properly, they are using the same foot for the gas and the brake) DFCO activates anytime you are off-throttle, in gear and the momentum of the car is sufficient to keep the engine turning at more than about 1200 rpm. Given those two facts... is there any need to involve the brakes in the equation? If you're driving an automatic, DFCO is already activated even BEFORE you start braking, and will stay that way until the engine revs decrease to the point that the engine needs fuel to idle. With a manual, the same holds true until you put the clutch in, then the engine has to exit DFCO mode to idle. __________________ ----------------------- Loren@InvisibleSun.org -----------------------

02-03-2009, 08:07 PM	#3
smacky Drives: 2008 Liftback AT Join Date: Dec 2008 Location: Utah Posts: 14	From what I've observed DFCO will work until your braking reduces your speed and your RPMs get to 1000ish. Braking for a short time (around a second) will also shift you into the next gear down and that way you can keep your RPMs a little higher and DFCO will stay on a little longer. __________________

02-03-2009, 11:08 PM	#7
Loren What? Drives: 2007 Yaris LB Join Date: Nov 2008 Location: Safety Harbor, FL Posts: 1,006	Unless I'm hardcore hypermiling, I don't bother downshifting below 3rd gear on a DFCO coast-down. You can go pretty darned slow in 3rd gear before getting below 1000-1200 rpm. With an automatic, the transmission will automatically downshift as you decelerate and should keep your revs up until you're at a near stop, anyway. __________________ ----------------------- Loren@InvisibleSun.org -----------------------

02-04-2009, 11:00 AM	#9
Sodium Duck ╚══════════RN Drives: 2008 Liftback Join Date: Oct 2008 Location: Western Mass. Posts: 999	I thought that DFCO turns off when you hit the brakes? I remember reading that somewhere on the forums. __________________ 42.88

02-03-2009, 09:50 PM	#6
MadMax Drives: 2008 Yaris Liftback (Sprocket) Join Date: Oct 2008 Location: San Antonio, Texas! Posts: 2,799	So, does it make sense to downshift the automatic to keep engine decelerating occurring as long as possible? I've gone down as far as second gear on my auto a few times; but I've often wondered, is it putting increased wear and tear on my transmission just to save a few drops of gas? I gotta admit, this DFCO feature intrigues me and I am trying to maximize its use! Cheers! M2

02-04-2009, 11:03 AM	#10
eTiMaGo vroom vroom View User's Garage Drives: lil red 5-door Join Date: Sep 2006 Location: Bangkok, Thailand Posts: 7,744	nope, it only turns off when you hit the gas, or the engine gets below a certain speed __________________ The price of freedom of religion, or of speech, or of the press, is that we must put up with a good deal of rubbish. - Robert Jackson Bye bye 1NZ...

02-04-2009, 12:56 PM	#11
Sodium Duck ╚══════════RN Drives: 2008 Liftback Join Date: Oct 2008 Location: Western Mass. Posts: 999	My idea has become a reality. =] __________________ 42.88

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