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Car so nice, bought twice
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My understanding is that they don't cut off the fuel when coasting in neutral because the engine will stop turning over and all engine driven accessories will no longer work.
Yep, I tested this on the way home tonight and the engine runs while coasting in neutral. Was getting 60 mpg @ 25 mph, which is better than I would have gotten in D (< 30 mpg) at those speeds while coasting.
 

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Be careful coasting at speed. AFAIK ESP/VSA/VSC does not work in neutral. Correct me if I''m wrong.
 

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Discussion Starter #23
Manual Car:

Did engine braking down the mountain to Half moon bay, I was a little disappointed that it basically didn't count towards the current MPG(I reset the trip computer right before the downhill while the fuel was shut off). So basically, got lower average MPG from the uphill climb, and wasn't able to counter it with the free mpg from the downhill. I only got a read out of 199.9(absolute max for the computer I'm guessing) after I tapped the gas pedal towards reaching the end of the downhill.

Maybe that's why whenever I hand calculate my MPG, it's always .5 mpg lower than what it actually is.
 

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This ^^^

Most cars have been doing it since OBD-II was introduced in 1996.

Jay
Hondas certainly haven't.

I had a Scangauge plugged into my 2001 Accord Coupe V6. Fuel usage in GPH never went to zero regardless if I was coasting or not.

I should plug the Scangauge into my 2014 to see if it does so now. That would answer the question for all of us. :) The biggest challenge would be finding it.
 

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Even My Mower Is a Honda!
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Hondas certainly haven't.

I had a Scangauge plugged into my 2001 Accord Coupe V6. Fuel usage in GPH never went to zero regardless if I was coasting or not.

I should plug the Scangauge into my 2014 to see if it does so now. That would answer the question for all of us. :) The biggest challenge would be finding it.
Most cars have a return to the tank sending unit, no? Just because the fuel pump is running does not mean the injectors are firing. I am assuming the scan gauge is just looking at pump pressure/flow?

I can tell when the injectors kick back on on my accord manual, it's at about 1500rpm. On my challenger it was 1,000rpm.

Jay
 

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Most cars have a return to the tank sending unit, no? Just because the fuel pump is running does not mean the injectors are firing. I am assuming the scan gauge is just looking at pump pressure/flow?

I can tell when the injectors kick back on on my accord manual, it's at about 1500rpm. On my challenger it was 1,000rpm.

Jay

I think it's right around 1300. If I'm in second and coasting down, the instant fuel gauge will indicate a drop in mpg right below 1300.




I believe that for fuel economy means of stopping are ranked thusly:

Best: coasting engine off
Coasting engine on
Engine braking
Worst: normal brakes.

Coasting is best because it conserves the momentum but if you have to stop more quickly engine braking is preferred because then there is less fuel being used while you waste the momentum.
 

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Even My Mower Is a Honda!
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I think it's right around 1300. If I'm in second and coasting down, the instant fuel gauge will indicate a drop in mpg right below 1300.




I believe that for fuel economy means of stopping are ranked thusly:

Best: coasting engine off
Coasting engine on
Engine braking
Worst: normal brakes.

Coasting is best because it conserves the momentum but if you have to stop more quickly engine braking is preferred because then there is less fuel being used while you waste the momentum.
Yes, and you can feel the car push forward just a little bit.

Jay
 

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Either during coasting/engine braking, and if it does shut off, how long till it does?

Owners manual seems to not have anything on this
Yes. Instantly.

And uphill minus downhill is, always has been, and most likely always will be greater than zero fuel consumption.
 

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Corvalis TTX
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Most cars have a return to the tank sending unit, no? Just because the fuel pump is running does not mean the injectors are firing. I am assuming the scan gauge is just looking at pump pressure/flow?

I can tell when the injectors kick back on on my accord manual, it's at about 1500rpm. On my challenger it was 1,000rpm.

Jay
A lot of modern cars no longer have the return line to the tank. The fuel pump does not run constantly on these cars but is rather duty cycle controlled.

Not sure how scangauge is calculating fuel flow but most on board fuel consumption computers calculate fuel usage from injector "open" times.

I know for sure my 97 XJ6 cuts off fuel flow because I've had an oscilloscope attached to two injectors and, when coasting, the injectors are not triggered. Haven't tried this on my Accord yet - maybe a summer project.
 

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Even My Mower Is a Honda!
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A lot of modern cars no longer have the return line to the tank. The fuel pump does not run constantly on these cars but is rather duty cycle controlled.

Not sure how scangauge is calculating fuel flow but most on board fuel consumption computers calculate fuel usage from injector "open" times.

I know for sure my 97 XJ6 cuts off fuel flow because I've had an oscilloscope attached to two injectors and, when coasting, the injectors are not triggered. Haven't tried this on my Accord yet - maybe a summer project.
Also our cars have a 2nd pump for the DI as well from what I've read on here.

Jay
 

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I have a 2005 Acura TSX and I can look at the raw data for the fuel economy, they are periods when the Fuel used shows 0 for extended periods when I am coasting, but only over certain speeds. So I think there are times the fuel injectors are turned off at least in an automatic transmission car.
 

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Yes, the fuel injectors can cut off while coasting when certain conditions are met.

I have heard that coasting in gear will net better mileage than coasting at idle.
 

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Elvira - the car
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From what I understand, the fuel injectors close, quit delivering fuel, when the rpm is over 1000-1200 rpm with the engine in gear and foot off the accelerator.

When you put the trans in Neutral you are dropping the RPM to 700-750, way below the 1200 RPM limit. So fuel starts to flow again.

Since your trans is in gear, the wheels are now turning the trans which in turn keeps the engine spinning turning the engine into a "compressor" without the explosions pushing the pistons. Your car then slows down from the resistance of all that work(engine braking). Put it into N and you can coast further, right? You just disconnected the engine from the trans and wheels.

There's a hypermiler trick of sorts that you constantly keep in mind the DFCO (deceleration fuel cut off)rpm and accelerate then coast alot. You're using the forward momentum to keep you going until get to the DFCO limit then accelerate slowly again.

I think i described that correctly. Corrections welcome:yes:
 

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Hondas certainly haven't.

I had a Scangauge plugged into my 2001 Accord Coupe V6. Fuel usage in GPH never went to zero regardless if I was coasting or not.

I should plug the Scangauge into my 2014 to see if it does so now. That would answer the question for all of us. :) The biggest challenge would be finding it.
Zorinlynx, I'm going from memory here. I don't have my scangage OM in front of me. If I remember correctly you have to set the fuel cut-off point on your Scan Gage, and it is best set at a throttle position value of 4 above the closed throttle value which may not be zero on some cars. Set fuel cut-off wrong and you might never see zero fuel flow indicated, or 9999 for instantaneous MPG.
 

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From what I understand, the fuel injectors close, quit delivering fuel, when the rpm is over 1000-1200 rpm with the engine in gear and foot off the accelerator.

When you put the trans in Neutral you are dropping the RPM to 700-750, way below the 1200 RPM limit. So fuel starts to flow again.

Since your trans is in gear, the wheels are now turning the trans which in turn keeps the engine spinning turning the engine into a "compressor" without the explosions pushing the pistons. Your car then slows down from the resistance of all that work(engine braking). Put it into N and you can coast further, right? You just disconnected the engine from the trans and wheels.

There's a hypermiler trick of sorts that you constantly keep in mind the DFCO (deceleration fuel cut off)rpm and accelerate then coast alot. You're using the forward momentum to keep you going until get to the DFCO limit then accelerate slowly again.

I think i described that correctly. Corrections welcome:yes:
Yeap, you are correct. On this Accord it seems that 1100-1150 rpm is the lowest end where DFCO stays active. Deceleration techniques vary based on the terrain. Some are better when you coast in neutral while others are better when you leave your car in gear.
 

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Zorinlynx, I'm going from memory here. I don't have my scangage OM in front of me. If I remember correctly you have to set the fuel cut-off point on your Scan Gage, and it is best set at a throttle position value of 4 above the closed throttle value which may not be zero on some cars. Set fuel cut-off wrong and you might never see zero fuel flow indicated, or 9999 for instantaneous MPG.
Does this mean that the Scangauge isn't showing ACTUAL fuel consumption as reported by the ECU, but rather is estimating it based on other data? That would kind of ruin the point of a scangauge, me thinks. The ECU should know exactly how much fuel is being provided to the engine at any given moment.
 
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