Best habit to shift gears on MT and fuel economy

[jwlee7ucla]

Originally Posted by Pete156

Coasting out of gear is technically illegal in most states.

Sorry, but you are wrong about coasting in gear. When you coast in gear, you do consume gas. If you didn't, your engine would stop running. The amount of fuel is indeed much less, but the engine is still burning fuel while coasting in gear. Even an engine driven by the wheels burns gas.

a quick install of an air/fuel ratio gauge will prove you wrong.

[daiheadjai]

Originally Posted by jwlee7ucla

a quick install of an air/fuel ratio gauge will prove you wrong.

Actually, if you leave the car in gear for a downhill and put on the instantaneous MPG reader, it will show 0.0 (comparatively, if you are stopped, it shows -.-).

The engine needs to keep turning - it will either do this using the rotation of the wheels, or by idling.

[Trashed675]

If the car is in neutral, while coasting down hill, the engine has to use a little bit of fuel to keep the engine from dying.

If you leave it in gear it does not use any. Its the same principal as a bump start, only with fuel instead of spark. You don't technically need fuel to make an engine turn, just like you don't technically need a spark, compression works just fine in that case.

Depending on your speed and the gradient of the hill youre rolling down popping the car into neutral might not be such a bad idea since it will still be using a VERY small amount of fuel, and you'll get "enough" drive just from gravity and forward momentum, as opposed to leaving it in gear and slowing down more quickly....you won't cover as much ground.

[Toyarzee]

Originally Posted by 993Fan

This might be of interest...

http://www.popularmechanics.com/cars...l-fuel-economy

Originally Posted by jwlee7ucla

a quick install of an air/fuel ratio gauge will prove you wrong.

Yes.

Does anyone know the stock ecu high and low fuel cut threshold?

[Pete156]

Originally Posted by jwlee7ucla

a quick install of an air/fuel ratio gauge will prove you wrong.

Please teach me. What part of what I said will an AFR gauge prove wrong?
Please continue

[Pete156]

Originally Posted by 993Fan

This might be of interest...

http://www.popularmechanics.com/cars...l-fuel-economy

This article has absolutely NOTHING to do with what I said. Don't know why you are pointing it out to me. I know this stuff.

[Cyau]

[jwlee7ucla]

@ Pete
When coasting in neutral you will see 14.7 ( just like idle). When you coast in gear you will see an error code ( because no fuel). The wheels keep the engine rotating so no combustion is needed. Just do a quick Google search for 'does coasting in gear use no fuel' and you should be able to find a plethora of links to explain why

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[gutbuster]

For economy I shift 1-2-4-6 from stops. If rolling then 2-4-6 and cruise. Shift early, heavy on the gas (but not lugging) to reduce throttling losses. When I'm looking for fun then I use all gears. I average around 33 mpg, partly because Ive only got 1400 miles on it and am observing some break-in protocols. I'm sure as I get used to letting it sing the higher notes that may change. But steady state cruise is pretty damn good.

When the C5 Corvette came out it had a lockout to skip I think 2nd and 3rd under low accel (high manifold vacuum).

[Nasty Sausage]

I average a little over 32MPG according to ye ole calculator method. I time my rate of speed to slowly decrease in whichever highest gear whenever I spot a red light, maybe 500 yards or more in front if possible. I use "V-Power" 93. Nine times out of 10, I do not come to a complete stop before the light turns green, much to the chagrin of fellow Floridian drivers who must race to the red lights and flick you off!

[Pete156]

Originally Posted by jwlee7ucla

@ Pete
When coasting in neutral you will see 14.7 ( just like idle). When you coast in gear you will see an error code ( because no fuel). The wheels keep the engine rotating so no combustion is needed. Just do a quick Google search for 'does coasting in gear use no fuel' and you should be able to find a plethora of links to explain why

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You can believe the computer if you want.
By this (your) on-line theory, we should be able to breathe the air emitted from the exhaust pipe while we coast twenty miles down the western slopes of the Cascade mountains here in western Washington. Well let me tell you something, you will die if you do so! As long as the engine is "running", it is burning fuel. That exhaust has both CO and CO2 in it, proving that there is some type of fuel being combusted in the cylinders, despite what the computer readout is. If it were just air we would be able to breathe it.
When we activate the clutch after coasting in gear does the car shut off? No, it does not. Are we 'bump starting' it? No we are not.

[jwlee7ucla]

Originally Posted by Pete156

You can believe the computer if you want.
By this (your) on-line theory, we should be able to breathe the air emitted from the exhaust pipe while we coast twenty miles down the western slopes of the Cascade mountains here in western Washington. Well let me tell you something, you will die if you do so! As long as the engine is "running", it is burning fuel. That exhaust has both CO and CO2 in it, proving that there is some type of fuel being combusted in the cylinders, despite what the computer readout is. If it were just air we would be able to breathe it.
When we activate the clutch after coasting in gear does the car shut off? No, it does not. Are we 'bump starting' it? No we are not.

I take it you are too lazy to do some research.

From just 1 of many links:

"The Keep it in Gear Camp: Keeping it in gear, the vehicle's computer senses the reduction in power demand and shuts off fuel to the fuel injectors. When costing in gear, the engine is essentially off. This added resistance acts like an engine break, slowing the vehicle down but it does so with almost no fuel consumption.
"

Most new cars have fuel-cut off, where above a certain speed the injector duty cycle will be 0.

So its not just "my computer", it is everyone's computer.

You know even the instantaneous mpg reading on the frs shows 127 (If i remember correctly) when you coast in gear right?


http://groups.engin.umd.umich.edu/vi...ganesan_w2.pdf

page 140.

Game.Set.Match

[SirBrass]

Edit: delete, please

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[strat61caster]

Originally Posted by Pete156

Well let me tell you something, you will die if you do so! As long as the engine is "running", it is burning fuel.

http://en.wikipedia.org/wiki/Energy-...ing_or_gliding

When coasting with the engine running and manual transmission in neutral, or clutch depressed, there will still be some fuel consumption due to the engine needing to maintain idle engine speed. While coasting with the engine running and the transmission in gear, most cars' engine control unit with fuel injection will cut off fuel supply, and the engine will continue running, being driven by the wheels.

The technology has been around for at least 20 years. You bet your ass the fuel injectors stop injecting fuel when coasting in gear, or at least a significantly reduced amount.

Here's a paper from 2009 where the abstract talks about how (5 years ago) modern vehicles use almost zero fuel whilst coasting:
http://papers.sae.org/2009-01-0416/

I tried to find the original paper proving fuel shutoff was possible and beneficial but no luck.