Coast in-neutral vs in-gear: I've been challenged to show the numbers

[reb01501]

Originally Posted by ecomodded

You have established absolutely nothing, besides being ill informed and slightly obnoxious,That i got.

I apologize for the obnoxious tone - it came from too many debates in the past few days, as well as surprise at seeing the assertion made so many times on this forum be disputed.

So, I have read countless posts and articles to come to my conclusion that zero gas is used to keep the engine running during DFCO, including myriad posts on this forum. You're telling me I'm "ill informed". OK, please tell me specifically what I'm ill-informed about and what I need to read to correct that misinformation. Thank you.

Tell me how you suggest one measure for results?

The same way gealii, and now Whitey have done. By documenting the change in the amount of fuel they used to drive the same routes, changing only coasting-in-gear to coasting-in-neutral. Whitey's report is especially convincing to me, since he used multiple tanks with each technique, and therefore minimized the effects that minor route changes and traffic fluctuations would have on his results.

For a more controlled test, I suggested one on the first page, no need to repeat it here I think.

[Fat Charlie]

Originally Posted by Whitey

I cruise at 57 MPH, and usually I'm able to maintain that speed during my neutral coasts. I had been unable to maintain that speed when "coasting" in gear and used a lot more gas. The evidence is in my fuel log (click the Honda badge in my signature). My last three tanks have been my three best tanks, averaging 47.01 MPG. The three tanks prior to those averaged 42.78 MPG.

-Doug "Whitey" Jackson

Beautiful job! Unfortunately, that's where the obvious factor comes in- are you going to A-B-A it and do three tanks without neutral to verify it, or will you refuse to waste that much gas "proving" something that obvious?

[user removed]

I have no means to test the two scenarios in your original post, so hard data is not available to me. What I do have is a 45+ MPG average for close to 6k miles that shows I am fairly economical with my Fiesta.
I don't worry much about "challenges" from anyone.
What I do know is that the basic principle is the conservation of momentum. If I coast in neutral at an average speed of 50 MPH then I am using the fuel consumption at idle to keep my engine running which would be more then if I coasted with the engine off.
With the engine running I have no fear of a catastrophic transmission failure due to lack of lubrication.
My strategy is to coast in neutral (engine running) while getting well over a hundred MPG to the greatest extent possible. When outside influences force me to decelerate at a greater rate, something I try to avoid like the plague, then I shift back into drive and let engine braking slow me down at a faster rate. When that fails to provide the necessary deceleration, I am forced to apply the brakes which turns my precious inertia into heat and brake dust.
Whether my technique is more or less efficient is based on my understanding of the fact that having the engine bleed off vehicle speed or idling at a consumption rate of about .15 GPH depends on my failure to prefectly anticipate every deceleration event I may encounter in a round trip of 40 miles with 46 traffic lights that could force me to stop, instead of 40 miles of 45 MPH highway where I would never have to stop.
I guess in the final analysis it really depends on your situation. If stopping is unavoidable the use engine braking, but if you have the means to anticipate and prevent the deceleration events in the first place then engine drag deceleration would be avoidable as well as friction braking. If I had the ability to wipe the 46 traffic lights off of my drive, and eliminate all the traffic that can force me to stop, I probably could get 60 MPG instead of 45.
While the argument that using no fuel versus having the engine idle while coasting in neutral has some validity, the most relevant fact is your driving environment, which can force you to take actions that are unavoidable. Without actually driving your normal route, it is impossible for me to develop a strategy to maximise fuel consumption in your particular scenario.
Give me a country road with shallow hills and no traffic to disturb and 70+ MPG would be a potential result. Sadly my wife needs to be close to a Wal-Mart to be truly content.

regards
Mech

[reb01501]

I think between gealii and Whitey, my "challenge" has been met and the ball is now in my challenger's court, so I thank you all.

As other's have said, Whitey's results would have been more convincing if he had done ABA, or randomized the technique used for each tank, something like 1-3-6 using in-gear coasting and 2-4-5 using neutral coasting. But I do understand how hard it is to forego savings for the sake of science.

[Whitey]

Originally Posted by Fat Charlie

Beautiful job! Unfortunately, that's where the obvious factor comes in- are you going to A-B-A it and do three tanks without neutral to verify it, or will you refuse to waste that much gas "proving" something that obvious?

Thank you. It'll be Option B for me. I'm 100% convinced already. A-B-A testing would be a waste of fuel.

I use a Scangauge. Downhill on the highway, the real-time MPG readings jump from about 70 MPG to over 260 MPG immediately after selecting neutral. Also, my vehicle sometimes will accelerate in neutral, so I'll be clicking off even more miles for the same amount of "idle" fuel consumption while gaining momentum instead of losing it. I've seen readings of over 320 MPG...

Scangauge also has allowed me to track fuel efficiency for each trip. Prior to using neutral on the highway, I was doing well to average 45 MPG on a trip. Now I routinely average better than 50 MPG. My latest three-tank average would have been better if I hadn't got stuck in horrible stop-and-go highway construction traffic on several of my recent trips.

Coasting in neutral is the most productive "mod" I've made. I encourage people serious about conserving fuel to try it for themselves.


-Whitey

[Fat Charlie]

Sweet. My rig doesn't cruise at much over 210 mpg- I have to shut the engine off to get good numbers. Pity nobody scientifically verifies these things.

[ecomodded]

reb01501: Fuel cut-off during deceleration is of the adapted type. When the throttle is closed and the r.p.m. exceeds 1,700 (for engine speeds lower than 1,700 r.p.m., the cut-off function is not operative in order that an optimal drive-ability can be maintained) the injection of fuel is disactivated. If the supply is interrupted, the r.p.m. will start to fall more or less quickly in relation to vehicle conditions. Before reaching idle speed, the dynamics of the fall in r.p.m. is checked. If this exceeds a certain value, the fuel supply system is partially reactivated on the basis of a logic which envisages the "soft accompaniment" of the engine at idle speed. When this condition has been reached, the normal functions at idle speed are reactivated and cut-out during deceleration will only be reactivated if the fuel cut-off threshold is exceeded to prevent the engine from jerking. The reactivation thresholds for the fuel supply and cut-off vary in relation to engine temperature.
Another fuel cut-off logic has been developed within the control unit which intervenes during partial deceleration, ie. when a lower engine load is requested. The function is only activated if the new conditions last for a set period of time and after the ignition angle has been adapted to the new situation.

Reb, i can easily come off as slightly obnoxious myself at times,despite having no interest in being obnoxious.
Thanks for clarifying your intent.

[reb01501]

Originally Posted by ecomodded;320787

Read more: Driving Tips to Save Gas - Memorial Day Weekend - Popular Mechanics

[url=http://www.popularmechanics.com/cars/news/fuel-economy/6-driving-tactics-to-save-gas-this-weekend-2

Driving Tips to Save Gas - Memorial Day Weekend - Popular Mechanics[/url]

Actually, this is the one I was trying to refute:
Coasting in Neutral or Gear to Save Gas - Coasting and Fuel Economy - Popular Mechanics

Here's a bit of it for those who hesitate to follow links:

I've replicated these conditions with instrumented cars, both with scan tools and with an oscilloscope, measuring the leads leading into the fuel injectors. The signal controlling the injector is a 12-volt square wave. It's pulse-width-modulated, varying from 5 percent or so at idle to around 80 percent or so at full throttle. The higher the percentage of on time to off time, the more fuel. There's one on pulse for every cylinder firing, so the consumption also varies with engine speed (rpm). All vehicles show a short pulse width at idle, regardless of whether they're sitting in traffic at a red light or coasting downhill—at idle—in neutral. (Actually, they use a fraction more fuel sitting in drive at a traffic light, because of the drag in the torque converter, but I digress).

Almost all vehicles show a pulse width of zero when coasting while in gear. Zero, as in there is no fuel injected at all. Yes, the engine is turning over, the pistons are going up and down, the water pump, alternator and a/c compressor are working, so technically you can say the engine is running, sort of. But it's not consuming any fuel. And that goes for automatic or manuals.

Okay, eventually, at the bottom of the hill or as you creep up to the traffic light, the engine finally will slow to idle rpm—at which point the fuel injection will wake up and start adding fuel to keep the engine from stalling. That usually starts at around 1000 rpm, and if you pay attention, you can sense when it's happening as the engine will rev up slightly. And that's when the scan tool or oscilloscope will show injector dwell rise from 0 to 5 to 10 percent. So you're actually wasting gas by putting your car into neutral.

I hear this argument as well: My car-mileage-information computer goes wild with increased mileage while coasting.

The algorithm the trip computer uses is not based on how much fuel is actually consumed, but on some calculated value based on airflow past the mass airflow sensor, manifold vacuum and engine rpm. And it's not accurate under these coasting conditions. That's why when we report fuel economy here at PM, we never just print the numbers we read off the trip computer's display: We use the gallons pumped into the tank divided by the mileage on the odometer—which we check against a handheld GPS.

I use a Scangauge II for a lot of diagnostics and general tinkering. It's a great tool—but I've learned not to trust the economy or gallons-used function too closely. That's why the Scangauge has a function that allows you to tell it what the engine-idle cutoff is for your particular car to get somewhere closer to the truth.

[reb01501]

Originally Posted by ecomodded

reb01501: Fuel cut-off during deceleration is of the adapted type. When the throttle is closed and the r.p.m. exceeds 1,700 (for engine speeds lower than 1,700 r.p.m., the cut-off function is not operative in order that an optimal drive-ability can be maintained) the injection of fuel is disactivated. If the supply is interrupted, the r.p.m. will start to fall more or less quickly in relation to vehicle conditions. Before reaching idle speed, the dynamics of the fall in r.p.m. is checked. If this exceeds a certain value, the fuel supply system is partially reactivated on the basis of a logic which envisages the "soft accompaniment" of the engine at idle speed. When this condition has been reached, the normal functions at idle speed are reactivated and cut-out during deceleration will only be reactivated if the fuel cut-off threshold is exceeded to prevent the engine from jerking. The reactivation thresholds for the fuel supply and cut-off vary in relation to engine temperature.
Another fuel cut-off logic has been developed within the control unit which intervenes during partial deceleration, ie. when a lower engine load is requested. The function is only activated if the new conditions last for a set period of time and after the ignition angle has been adapted to the new situation.

Yes, there is a bit there I hadn't realized, but, I have been very careful to say "while DFCO is in effect", so I wasn't that far off.

[PaleMelanesian]

On most Hondas the cutoff is at 1100 or 1200 rpm. Above that you get fuel cut.

Watch a scangauge for the Open Loop condition. That means the computer is not watching the exhaust O2 sensor reading. There's no need to, and no need to adjust the fuel flow, if there is no fuel going in to start with.

It's not scientific, but I never use DFCO in my hypermiling. I get good results from that, among other techniques. (and I don't have to guess whether the gauge is handling it correctly)