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Old 11-03-2012, 07:24 AM   #1 (permalink)
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Isn't it more efficient coasting in gear/engine on?

From what I understand, Almost all modern car engines shut off the injectors when the engine is down revving, foot off the gas in gear.

Sure, I won't coast as far a the proponents on here who coast in neutral, engine off...which is very dangerous, and in most jurisdictions, very illegal.

Even coasting in neutral with the engine idling will waste more gas than engine even braking, as is see it.

Thoughts?

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Old 11-03-2012, 11:36 AM   #2 (permalink)
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1. topic is addressed in other threads.
2. 'all modern engines??????? 1984 and up? 1999 and up?
3. Majority of posters here have 'older' cars.
4. the issue of engine on/ neutral coasting has been determined to be manufacturer specific. Alos addressed in other threads.

for example, the last year of the ford taurus (mayby older ones also) DOES NOT gain any advantages. the rpms DO NOT drop
My 02 (02-06) Infiniti Q45 DOES benefit from engine on/ nuetral coasting DOES make a difference.
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Old 11-03-2012, 12:06 PM   #3 (permalink)
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My car at 40 MPH, in neutral: ~245 MPG
My car at 40 MPH, engine braking (3rd gear) ~130 MPG

Conclusion: The Toyota Yaris manual transmission DOES NOT DFCO. Approximately twice as many MPG's in neutral.

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Old 11-03-2012, 12:48 PM   #4 (permalink)
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Quote:
Originally Posted by wungun View Post
From what I understand, Almost all modern car engines shut off the injectors when the engine is down revving, foot off the gas in gear.
As mr M says this has been covered - the simple answer is "it depends". Firstly are you looking to maintain as much momentum as possible to coast as long as you can (on the flat) - in which case out of gear wins. Or are you going downhill or slowing to a stop then if your ECU cuts off the injectors in gear wins.

If your car can handle it, and it is legal where you are and you are in full control engine-off wins - the Prius turns the engine off when it can.

You also need to know your car - for example in my Aygo it won't go into fuel shut off mode unless the engine rpm is over ~1400. In a low gear this results in a lot of engine braking, in a high gear less.

So as I tapped it depends - on the scenario, your car and what you feel comfortable with.

Quote:
Originally Posted by Flakbadger View Post
My car at 40 MPH, in neutral: ~245 MPG
My car at 40 MPH, engine braking (3rd gear) ~130 MPG

Conclusion: The Toyota Yaris manual transmission DOES NOT DFCO. Approximately twice as many MPG's in neutral.
Does yours have the same rule as mine - i.e. > 1400 rpm ? These results could be due to the fuel required to maintain idle (~900 rpm) out of gear vs what the ECU thinks is needed at whatever rpm in 3rd at 40 MPH is - I would google this last factor but your US Yaris might be different from our UK one.
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Old 11-03-2012, 12:49 PM   #5 (permalink)
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..as is see it.
Until you have done tests, you haven't seen anything.
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Old 11-03-2012, 12:52 PM   #6 (permalink)
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With deceleration fuel cut-off (aka engine braking) you have no fuel used but the engine is slowing the car down a lot faster than in engine-on neutral coasting, where you have the engine idling but not slowing the car down.
DFCO will obviously save fuel if you were slowing down anyway.
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Old 11-03-2012, 02:14 PM   #7 (permalink)
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Even if your engine has DFCO, it is still losing some energy from friction (pistons going up & down, &c) and from pumping losses, so obviously it is not more efficient.

The danger/illegality issues have been addressed elsewhere, so I'll just point out that what you believe - coasting is unsafe, big SUVs are safer than small cars, all your kids are above average - may not match reality :-)
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Old 11-03-2012, 02:30 PM   #8 (permalink)
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Quote:
Originally Posted by Flakbadger View Post
My car at 40 MPH, in neutral: ~245 MPG
My car at 40 MPH, engine braking (3rd gear) ~130 MPG

Conclusion: The Toyota Yaris manual transmission DOES NOT DFCO. Approximately twice as many MPG's in neutral.

Cheers.
Where are you getting your information for this? If you are using your Ultragauge you have to tell it if you have DFCO it won't tell you.
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Old 11-03-2012, 03:25 PM   #9 (permalink)
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Quote:
Originally Posted by jamesqf View Post
.

The danger/illegality issues have been addressed elsewhere, so I'll just point out that what you believe - coasting is unsafe, big SUVs are safer than small cars, all your kids are above average - may not match reality :-)
1 outa 3... .......My daughter is above average!!!!!!!
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Old 11-04-2012, 06:21 AM   #10 (permalink)
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Quote:
Originally Posted by wungun View Post
From what I understand, Almost all modern car engines shut off the injectors when the engine is down revving, foot off the gas in gear.
We call it engine braking, and as it's braking, it's inefficient - unless you need to brake of course.
I've been doing that all my driving life, and it give fairly good mileage.

But if you want to do better than fairly good, you'll also need to drive differently ...
Quote:
Sure, I won't coast as far a the proponents on here who coast in neutral, engine off...which is very dangerous, and in most jurisdictions, very illegal.
The legal issues that remain here and there, will have to go as all priusses coast ...
They exist from days when brakes were nearly useless and unreliable, so engine braking was almost mandatory to slow down.

Quote:
Even coasting in neutral with the engine idling will waste more gas than engine even braking, as is see it.
Thoughts?
You're seeing it wrong
Coasting with the engine on instead of engine braking is what has helped bring down my fuel consumption from already "fairly good"

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