Why does my car consume fuel even when coasting (09 Accord I4 automatic)

[WesternStarSCR]

+1 for different cars - different setups - different variables

My choices are as simple as knowing if I am going to have to stop soon or not.

When I back off the throttle, I can feel the differences between being in 4th on my auto trans, or if I slide into neutral. I go much farther when i am cresting a hill at 60 then slip into neutral, than if i keep it in D and take foot off of gas.

The point I saw on the "Hypermiling an iVTEC Honda" thread was basically yes, one can argue that instant Fuel Consumption is higher in neutral at speed then at DFCO.

But that does not account for the ENERGY lost by having the engine being turned by the wheels in DFCO. The energy lost more than makes up for potential idle consumption for x amount of seconds.

I have no UG or SG, but at least in my car, I have learned the spots on my route, and the situations, to either just stay backed off and in gear (approaching traffic or a light) vs putting in in neutral from time to time (cresting a hill, no traffic behind me to stack up, and a nice long roll to the next flat or hill when i am doing about 45 and put it back into D).

If nothing else, try to 'feel' what your car is doing, and it may answer your question.

YMMV

Cheers,

[roosterk0031]

DFCO and auto tranny's just don't work, don't worry about the fuel useage will idling and coasting, anytime with the cobalt and I'm coasting over 30 mph I'm 99+ mpg. since I have a manual I can DFCO on down hills if I down shift and keep my RPM over 2k, so I get engine breaking, really I should have started my coast sooner if I need the engine to slow me down.

Focus on not needing to use the brakes that's where the best gains are.

[mcrews]

Originally Posted by Xist

"with 2.2 million people in US prisons, that means there is about 1 lawyer for every inmate" Incarceration in the United States - Wikipedia, the free encyclopedia

Lawyers will never starve when they can litigate.

only about 10% of all offenders go to prison/jail.
Criminal law is only 15% of all law practiced.

your wiki stat is less than meaningless. it is randomly usless.

[SentraSE-R]

Xist, I found your post at subaruforester.org. You and jayliu1984 need to set up your devices (Ultra-gauges or Scangauges) to recognize DFCO. The UG EM v. 1.2 Injector Cutoff setup procedure is on page 50 of the Owners Manual.

MENU  UltraGauge Setup ..  Injector Cutoff

The SGII v. 6.0 fuel cutoff setup procedure is on page 16 of that Owners Manual.

Once you get your UG or SGII set up to recognize DFCO fuel cutoff correctly, you'll start seeing 0 fuel consumption, or 9999 mpg.

If you rely on a mfr OEM fuel consumption display (as I suspect jazyliu1984 may be doing), you're likely SOL.

[jamesqf]

Originally Posted by SentraSE-R

With the 6 speed transmission, DFCO didn't kick in under 70 mph in he Sentra in top gear. Worse, when it did kick in, it put the ECU in open loop for the next 4 minutes.

Why is this a problem? With the Insight, that's how I recognize that it's actually in DFCO (instead of just using little enough fuel that the realtime mpg gauge pegs out at 150 mpg) on a long downhill.

Or is it that it stays in open loop even after you add throttle again?

[MetroMPG]

Originally Posted by SentraSE-R

If you rely on a mfr OEM fuel consumption display (as I suspect jazyliu1984 may be doing), you're likely SOL.

FYI, the "instant" display in my dad's '02 Camry 2.4 automatic ( http://ecomodder.com/forum/showthrea...2-a-23818.html ) appears to show fuel cutoff.

[SentraSE-R]

Originally Posted by jamesqf

Why is this a problem? With the Insight, that's how I recognize that it's actually in DFCO (instead of just using little enough fuel that the realtime mpg gauge pegs out at 150 mpg) on a long downhill.

Or is it that it stays in open loop even after you add throttle again?

Exactly. It stayed in open loop for a full four minutes after I added throttle again. Any fuel savings from DFCO were negated by increased consumption during open loop operation.

The Sentra didn't like to get into DFCO, and after it did, it penalized me for getting there.

[ECONORAM]

Originally Posted by roosterk0031

DFCO and auto tranny's just don't work, don't worry about the fuel useage will idling and coasting, anytime with the cobalt and I'm coasting over 30 mph I'm 99+ mpg. since I have a manual I can DFCO on down hills if I down shift and keep my RPM over 2k, so I get engine breaking, really I should have started my coast sooner if I need the engine to slow me down.

Focus on not needing to use the brakes that's where the best gains are.

I don't follow. Both of my vehicles are automatics and have DFCO. The RAM only uses it for decel with a load--it is hard to get it to kick in with an empty truck. It will upshift a gear, relock the converter, and then cutoff fuel flow. I've watched it several times on the MPGuino.
The Avenger does DFCO in OD lock anytime you slow down from 63+mph...to about 55mph. Engine RPMs still happen, accessories still run for both vehicles.

I agree, learning how to NOT use the brakes so much is the best method.

[jayliu1984]

Originally Posted by MetroMPG

Jayliu - SentraSE-R is right - your gauge (ScanGauge, UltraGauge?) may not be properly configured to show when your engine is in fuel-cut.

Alternatively, you could also try monitoring the Loop status (Open/Closed). You might see that change (from closed to open) when the engine is in fuel cut mode even if the fuel/hour may not.

And I bet if you went on an Accord forum, someone with the factory service manual would be able to detail the exact conditions under which fuel cut occurs. As was said, it's different for different vehicles, and depends on a number of variables.

Hello MetroMPG, thanks for the tip! Now all the puzzle pieces are coming together.

I use a Chinese gauage that display 8 stats (2 are fixed to speed and instanteous MPG). I have configered it to display Fuel Status, and I have noticed very strangely that the car will enter "close loop" very quickly after start but it will almost always switch to "open loop - driving" (direct translation from on screen chinese) which baffled me until now.

I was wondering why would it entre "open loop-driving" no matter how light I step on the gas. And it always swtich to it AFTER I released the padel. I thought it was because lag, now I know better.

Next time I will try to switch to neutrul when it is in "open loop - driving", see if it will switch to close loop.

However, I can't seen to able to configure the device to recognize the mode.

For anyone who is interested, I do strongly recommand this product. Here is the english version on dealextreme which cost $100 (still cheaper than UG)

A301 Vehicle Car OBD Multi-Function Trip Computer - Black (3.0" LCD) - Free Shipping - DealExtreme

And since I am Chinese and have relative come visit me last month, I bought the Chinese version (exact same stuff just language) for only $40 equivalent.

[Occasionally6]

+ another one for different cars, different DFCO criteria.

Some vehicles may not use it very much, if at all. With DFCO there is air, admittedly a small amount of it, being blasted through the catalytic converter. That tends to cool it so there may be conditions where the capability of the cat. to reduce emissions is being protected (DFCO inactive), despite the readily apparent criteria being met.

In addition to the TPS and rpm inputs there's usually a MAF or MAP criterion. High airflow or manifold pressure will kick the ECU out of DFCO.

ECU's will do some interesting things while coasting. I can observe a constant MAP signal while coasting, regardless of differences in speed or gear. I suspect the ECU is moving the idle air control to prevent the MAP from dropping while being motored, avoiding unnecessary pumping loss. (Called sail on.)