How To Increase Your Gas Mileage

frost

^ interesting you say that, because when I'm looking at my instant fuel gauge, and I drop it into neutral, I will go into the 40mpg+ area, but it stays in the 20s if I just let off.
Thoughts?

ChrisSlicks

It goes 40+ in neutral but should go off the chart (60+) when you lift off completely.

frost

I'll have to give this a better look tomorrow, sure would be handy to stay in gear.

dad

Coasting in neutral consumes more fuel. In neutral, the injectors fire to keep the engine at idle, so you are burning fuel. Coasting in gear, the ECU switches to deceleration ... which happens to have an injector pulse width of zero.

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monthtrial

FYI: I'm no mechanic nor an auto engineer... just a dude using common sense and the fuel gauge read-out on my car...


I still don't understand why coasting in neutral would burn more fuel?

Are you suggesting that simply lifting OFF the gas consumes less fuel than placing the car in neutral to idle @ 750 RPM? I think there's a direct correlation between fuel consumption and RPM range - unless you're bogging the engine or loading it.

If your theory is correct, I could be driving down hill in second gear @ 6,000 RPM with my foot off the gas pedal (yet maintaining speed due to gravity & slope/grade) and save more fuel than popping it in neutral.

Very, very arguable, irrespective of however technical you may wanna get w/ injectors or widths.

Sure, there may be a point at which the speed one drives w/ the foot off the fuel pedal conserves fuel, but gearing and velocity have to be factored in and there comes a point where idling and maintaining a certain momentum (vs. losing momentum due to engine speed slowing the car) is more efficient.


Can you refute my non-technical assessment? If so, please do so in plain english.

wstar

Well, if he's right about the fuel getting cut during engine braking, then yes engine braking would save more gas than coasting. However, I find this hard to believe. Cut fuel = no more combustion. The drivetrain would simply be spinning the engine and sucking air through the pistons for compression braking, but without any ignitions happening (which means really they could cut the spark plug current off too). I suppose in theory this sounds possible, but I would think I would hear the difference between an engine that's undergoing combustion and one that isn't, and I would think the transition between the two states would be rather abrupt and noticeable. Sure seems pretty smooth to me.

I'm not saying it isn't true, I'm just saying I find it hard to believe

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ChrisSlicks

The mechanical noise of all the engine parts moving far exceeds any noise the actual ignition makes.

In full lift off the injectors do not fire (there may be no spark either, but I'm not sure). It matters not the gear or the RPM's as long as the engine is above idle speed. As you approach idle the injectors will begin firing again to prevent stall.

You do get great mileage in neutral as well because idle fuel burn is minimal and there are times where that is going to save more fuel than lift off if you can do it for longer. But if you're going down hill you absolutely should be in gear.

dad

There is a distinct change in pitch between accelerating and coasting.

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