[ale] [OT] - Ethanol-free gas in the Atlanta area? - and gas saving tips

Wed Sep 18 17:06:05 EDT 2013

Years ago when I was a Saab 9000 owner (and therefore well advised to 
understand the car's innards) I bought a book on Bosch fuel injection 
systems.  I recall that it said that the Jetronic system (which used a 
hot-wire air mass meter) shut off the fuel when the engine was in 
overrun; i.e., it was more fuel-efficient to let it slow down with the 
clutch engaged and use compression braking when coming up on a red light 
than it would have been to hold the clutch down or throw it into 
neutral.  I would assume that that's pretty universal behavior now.

On 9/18/13 2:08 PM, Ron Frazier (ALE) wrote:
>
> "Ted W." <ted-lists at xy0.org> wrote:
>
>> On 09/17/2013 07:40 PM, Ron Frazier (ALE) wrote:
>>> Hi All,
>>>
>>> I just experienced something fascinating in my car.  We've got two
>> car related threads going, but this one is also fuel related, so I'll
>> put it here.
>>> In the UltraGauge manual and in that Popular Mechanics article, I
>> read that many cars occasionally turn their fuel injectors off to save
>> fuel.  I sort of said yea, yea, all well and good.  But I also assumed
>> that my 2005 Hyundai Santa Fe and my wife's 2007 Hyundai Sonata didn't
>> have this feature.  Surely, I would have noticed it.
>>> So, I took the Santa Fe out to go have supper.  I had torque running
>> beside me on the android tablet.  When I was cruising down a pretty
>> steep hill, I took my foot totally off the gas pedal.  I kept one eye
>> on the fuel flow gauge on the tablet.  Of course, you'd expect instant
>> mpg to go up, which it did.  What I DIDN'T expect, and could hardly
>> believe, is that after a few seconds, the fuel flow went to ZERO.  It
>> didn't go down.  It went AWAY!  I was totally amazed.  So my car does
>> have this feature.  There was NO discernable difference in the feel of
>> the car versus when the injectors were on.  The momentum of the car
>> keeps the engine turning and the accessories running.  I don't know if
>> they have a way of removing cylinder compression or something.  When I
>> got to the bottom of the hill and tapped the gas pedal, the fuel flow
>> resumed and I got power exactly like I expected to and went up the
>> other side of the hill.
>>> This was totally fascinating.  Note that you have to be on a pretty
>> steep hill and going at a decent speed for this to work, at least in my
>> car.  If the ECU thinks it's losing the ability to keep things running,
>> it will re engage the fuel.  Now that I know what to look for, though,
>> I want to see how often I can make this happen while maintaining
>> safety.  Burning NO FUEL, and getting infinite MPG, even for a few
>> seconds, is very enticing.  I have a theory that touching the brake may
>> make this happen sooner, but I haven't confirmed this.  I have to
>> research that.
>>> If you have an addon gauge system for your car, either torque,
>> scanguage, ultragauge, or other, definitely turn on the fuel flow gauge
>> and watch it coasting down hills.  Ultragauge has configuration screens
>> specifically for dealing with injector cut off.  I don't know about the
>> others.
>>> I thought this was way cooler than dirt, to paraphrase the cliche, so
>> I'm passing it along.
>>> Sincerely,
>>>
>>> Ron
>> Ron, I would have been thoroughly surprised had you found your car, as
>> new as it is, /didn't/ have this feature. I drive a '99 Subaru Forester
>> and I use a ScanGaugeII to monitor my fuel consumption. When I leave it
>> in gear (it is a manual 5-spd) going down a hill the MPG reading
>> instantly jumps (and stays) at 99999MPG which leads me to believe the
>> fuel injectors are not in use.
>>
>> Cheers,
>> Ted W.
>
> Hi Ted,
>
> I guess the feature has been around for a while.  It's just not something I've ever known about.  And I've certainly never tried to make it happen, since I didn't know about it.  I'd usually keep a light foot on the gas all the way down the hill.  Now I'm trying to make it happen when practical.  Seeing the fuel flow read zero was very neat.  Your ScanGauge might do that if it has a fuel flow gauge in the menu.  But, since it's reading 99999 MPG, I'd also agree that you're achieving fuel cutoff.
>
> My wife's car has it too, but hers freewheels down a hill so fast, while still having minimal engine braking, that you have to downshift her automatic transmission from 4th (D) to 3rd to get the injector cutoff, as going down in 4th doesn't keep the engine spinning fast enough to cut the fuel.  I doubt she'll be messing with the gear shift.  Her Sonata has a 2.4L engine and it only weighs 4000 Lbs or so.  So it gets pretty good MPG anyway, around 24 MPG.
>
> My Santa Fe has a 2.7L engine and weighs 5000 Lbs or so, so it doesn't do so well on MPG.  With my prior driving habits, I get around 17 MPG if I don't let it idle in parking lots and such.  I'd like to improve that a bit.  It's fairly easy to get that one to cut off it's fuel on a medium sized hill even in 4th gear.  It also has an automatic transmission.  Lesser hills make the car decelerate too rapidly to run for any substantial period of time.  You can also use the technique when cruising up to a traffic light some distance away.
>
> In testing my cars going down hills at say, 45 MPH with the cruise on, sometimes even if the car is gaining speed above the 45 MPH, it will not cut off the fuel.  Not sure why.  One time, it appeared to work, and others not.  It may be only possible to reliably use the technique with manual throttle control.
>
> I have conflicting data on what the brake pedal will do.  I thought it might trigger the cutoff.  But, I read on a forum somewhere that it kills the cutoff, ie re engages the fuel, because it may unlock the torque converter.  It may vary by vehicle.
>
> I read that on a manual transmission, pushing in (or disengaging) the clutch will re engage the fuel so the engine doesn't choke down.
>
> For some interesting reading, you can:
>
> Google dfco and the name of your car.  DFCO means deceleration fuel cutoff.
>
> https://www.google.com/search?output=search&sclient=psy-ab&q=dfco
>
> Google hypermiler - a person who always tries to beat the EPA MPG rating on their car.
>
> https://www.google.com/search?output=search&sclient=psy-ab&q=hypermiler
>
> Apparently, it's not too hard for some people to exceed EPA ratings by 30%.  For the Santa Fe, since it's rated at 18 MPG, I'd just like to get to the EPA rating.
>
> Sincerely,
>
> Ron
>
>
>
> --
>
> Sent from my Android Acer A500 tablet with bluetooth keyboard and K-9 Mail.
> Please excuse my potential brevity if I'm typing on the touch screen.
>
> (PS - If you email me and don't get a quick response, you might want to
> call on the phone.  I get about 300 emails per day from alternate energy
> mailing lists and such.  I don't always see new email messages very quickly.)
>
> Ron Frazier
> 770-205-9422 (O)   Leave a message.
> linuxdude AT techstarship.com
> Litecoin: LZzAJu9rZEWzALxDhAHnWLRvybVAVgwTh3
> Bitcoin: 15s3aLVsxm8EuQvT8gUDw3RWqvuY9hPGUU
>
>
> _______________________________________________
> Ale mailing list
> Ale at ale.org
> http://mail.ale.org/mailman/listinfo/ale
> See JOBS, ANNOUNCE and SCHOOLS lists at
> http://mail.ale.org/mailman/listinfo
>