Using DFCO to increase your MPG

[BailOut]

The engine keeps turning because the wheels are turning, which turn the axles, which turn the transmission, which turns the crankshaft, which makes the pistons move.

As stated in the original post the engine becomes a compressor rather than a combustor at this point. Think of it as the drive train operating in reverse... instead of the engine making the wheels turn the wheels are making the engine turn. Since your momentum and the wheels are doing all the work there's no need for the energy that fuel would provide, so the computer turns off the fuel injectors.

[Yaris Revenge]

It's strange to think your engine basically shuts down every time you take your foot off the excelerator.... freaky!

~YR

[ChinoCharles]

BailOut, can you feel this happen? For the last few weeks I have been playing with this and I think I can actually feel DFCO. In second gear especially, you'll feel the car kind of "smooth out" under decelleration. It almost feels like popping the clutch, only you're still in gear.

[BailOut]

ChinoCharles,

You took the words right out of my mouth. 2nd gear is where I, too, can actually feel this at, both entering and leaving DFCO. It's very subtle (which is a testament to Toyota's engineering) but it's there.

If I let my RPMs drop below 1,100 in 5th gear (which never happens unless I do it on purpose) I can feel it when the fuel kicks back in because it's like a surge from an old, tired spring.

[eTiMaGo]

Agreed, and it coincides with my AFR needle too, you can feel the tiniest of jerks a fraction of a second after you let your foot off the gas.

[ChinoCharles]

Cool! I'm going to try and really pay attention my next fill up and see if I can't get my already improving mileage numbers even better.

[nsmitchell]

I had a weird experience on my latest trips throught the hills of Virginia. I had my Rostra Cruise control going at 65MPH. Going down hills I felt the engine braking my speed so I maintained 65MPH even on a steep decline that you would normally speed up a lot on. (Coming down Afton Mountain in the Blue Ridge Mountains) I think this must have been DFCO, but I know my transmission stayed in 4th gear because I would have heard/felt my RPMs going up. Any thoughts? Could this be DFCO in action?
I tried finding infor on Rostra with no luck.

[churp]

I've noticed around town strange (compared to other automatic cars anyway) almost like what I've been thinking downshifting while slowing down. Just never noticed a perceptable change in other cars while slowing down....does the computer possibly do this (downshift/DFCO on its own) without manually downshifting....or is it just my imagination?

[BailOut]

nsmitchell and churp,

I can't answer your questions as I don't have an AT model to play with but it sounds to me like what you two have found is definitely possible.

[AustinYaris]

BailOut,

I still can't figure this DFCO thing out.

Here's a real life example:

There is a steady downhill grade on the street of my house that stretches for about a mile. Once I get over a small hill, I can coast in neutral for the entire mile at 40mph dropping to about 20mph before I need to turn.
- ScanGuage reads 200-230mpg during the run.

If I am in any gear, even 5th gear, I can not make this run without hitting the gas. There is too much engine resistance. At about half way, the car slows down to 20mph, so I have to hit the gas.
- ScanGuage reads around 140mpg for the run until I hit the gas.

In this scenario, isn't just coasting in neutral better for FE?

[BailOut]

AustinYaris,

Yes, in that case you're better off on neutral as you'll use less fuel idling the whole way down that grade than you would using DFCO for the first half and then using fuel for accelerating/maintaining the rest of it.

I cannot recommend the following to anyone not into hypermiling (this is my disclaimer so lay off the flames, please) but rather than just being in neutral for that span I'd be in neutral with the engine turned off and my ignition turned to the 2 position (Ignition II). This is called a Fas (Forced autostop) and the Yaris holds this posture very well as you still have PS (say thank you, drive-by-wire) and you also have PB for about 4 uses before you need to worry about anything.

The only drawback to Fas'ing is that the SG II turns off after 12 seconds. It doesn't really matter if you're already using DFCO, though, as the SG II doesn't read that properly and has already screwed up MPG and tank tracking.

[AustinYaris]

Thanks for the clarification.

I actually just tried FAS for the first time 2 days ago, and was even able to reengage ICE by shifting into gear and releasing the clutch. A lot easier than I imagined.

I didn't mention FAS since it would obviously be more fuel efficient than DFCO. Secondary reason, was to avoid the flames. You're a brave man to mention it... lol.

Appreciate the note about SGII as well. That's what I figured, but wasn't absolutely sure.

[Yaris]

With an automatic transmission, I find it more efficient to be in neutral when rolling down an incline, and then shifting to DFCO mode when I'm approaching an anticipated stop. I get the best mileage driving this way instead of always alternating between OD and DFCO. It doesn't make sense to accelerate with OD off when you can acceralate with OD on and then shift to neutral while cruising a fair distance before having to hit the gas pedal again.
I try not to accelerate at the exact moment I shift into drive because of the potential thumping of the transmission.
Does anyone know if shifting in and out of neutral while in motion is harmful to an automatic transmission?

[drifto]

its a very simple system. during braking above 1100 rpm the injectors cut off. i feel this every time i come to a stop sign etc. your not going to feel the car hold back as if you are breaking, but you will see the rpm drop down slightly lower than if you had the clutch in. if you find that your idle is too low or unchanged the car may not be PDI'd correctly. on honda/acura the cars have to be roadtested a certain way prior to delivery for the idle to be correctly adjusted during fuel cut off. it doesnt work if your in stop and go traffic. its been around for a long time actually. it was designed to meet emissions standards back in the mid to late 90's. hope this helps..

[Yarii]

I don't think it should hurt anything as long as you're not on the gas when you do it, and assuming you shift into the right setting (don't tell it to go from N into low at 60mph) but it'd be nice to get some more opinions...

Originally Posted by Yaris

With an automatic transmission, I find it more efficient to be in neutral when rolling down an incline, and then shifting to DFCO mode when I'm approaching an anticipated stop. I get the best mileage driving this way instead of always alternating between OD and DFCO. It doesn't make sense to accelerate with OD off when you can acceralate with OD on and then shift to neutral while cruising a fair distance before having to hit the gas pedal again.
I try not to accelerate at the exact moment I shift into drive because of the potential thumping of the transmission.
Does anyone know if shifting in and out of neutral while in motion is harmful to an automatic transmission?

[churp]

I've been shifting my auto into neutral and coasting and don't see a problem...anything under 55 slides back into gear nicely without giving it gas.

Older cars I know had a problem when moving without the engine rotating, due to no oil pumping without the converter going. Without oil circulating in the tranny while moving---lots of problems. Think they have cured this since front wheel drive, but don't know for certain. If the owners manual says no towing of an automatic without a dolly or trailer, this is the reason. Just to be sure I won't FAS with my automatic.

edit: Shutting the engine down with standard tranny no problem if you're comfortable/brave.... I'll coast with engine running w/automatic though!

[Yarii]

I think you're thinking of the automatics before (I think) like 1960... They used to have dual oil pumps, one off the engine side, and one off the driveshaft end... As transmissions became more reliable, the second pump wasn't needed, and it would in fact cause over pressure if you turned the engine off and costed downhill letting the rear pump build up pressure.... Lots of times it would blow tranny seals and spray the fluid onto the exhaust=big fire... On the plus side, you could push start those old automatics if you could get them moving fast enough since there was a pump that turned with the wheels (I've done it once on a buddy's vintage oldsmobile, pushing it with a pickup truck up to about 68kph before the torque converter had enough pressure on it to make the engine turn over) heh....

I've shifted in and out of neutral lots of times in my auto camry... Into neutral just isn't a problem ever - if you're coasting off the gas in OD, it basically puts itself into neutral anyway, but I've never tried putting it back into gear over 50kph just because I'm not sure how good that is for the system... When you think about it, I'd guess the stress of a shift from neutral into gear w/o touching the throttle isn't nearly as stressfull on the tranny as passing on the highway and having it kick down out of 4th into second with the throttle on the floor...

That said, in my old 88 crown victoria, I've done it lots of times, at highway speeds (100-120kph), and it never seemed to care. The electronics would think the throttle was wide open and to reset it (in order to slow down) you'd have to kill the motor and restart in neutral on the highway, and you didn't dare try pulling over to stop, or coasting to a slow speed... You try handling a 20yr old, 4000lbs car without power steering and a reserve canister so small you only get 1 shot of power assisted brakes... *looks for the smiley face of a car flying off the road into a tree*

Originally Posted by churp

Older cars I know had a problem when moving without the engine rotating, due to no oil pumping without the converter going.

[churp]

[QUOTE=Yarii;86587]I think you're thinking of the automatics before (I think) like 1960... They used to have dual oil pumps, one off the engine side, and one off the driveshaft end...

I was thinking more of the ones that didn't have the rear pump.....they couldn't be started by pushing because no oil was circulating, and if you towed them even short distances you could burn the tranny out. Probably not a problem anymore, I just like to play it safe...cause if it is a problem, once you notice it, it's too late.