Shifting into Neutral to Save Gas?

[zackwatt]

Originally Posted by Even Steven

Actually, it will not save you any gas. A little known fact about modern engine management systems is that they have the ability to cut off the fuel pulse entirely when coasting, such as a long downhill grade. Now, I'm not a Porsche mechanic, so I'm not 100% sure that Porsche does this, but I do know for a fact that most other manufacturers program their engine management systems to do this in order to raise their average fuel economy.

So the next time you're coasting down a hill, if you put your transmission into neutral, remember that you're forcing the computer to send fuel to your engine to keep it idling. If you were in gear instead, the fuel pulse may be shut off entirely by the engine management system, thus increasing your fuel economy.

If you doubt this, just do a little bit of research on the Internet and you'll discover it's true.

You Sir, Are Correct.

Modern engines use NO fuel to coast to a stop. In neutral there is no longer a mechanical linkage to the road to drive the rotation of the engine. Therefore something must be done to "run" the engine, so engine management must start the fuel flow.
Just think, you are getting those last few feet for FREE. YAY!

[JCL12]

Originally Posted by zackwatt

You Sir, Are Correct.

Modern engines use NO fuel to coast to a stop. In neutral there is no longer a mechanical linkage to the road to drive the rotation of the engine. Therefore something must be done to "run" the engine, so engine management must start the fuel flow.
Just think, you are getting those last few feet for FREE. YAY!

To Clarify: you are saying that when you coast in drive, all fuel flow ceases and engine RPM is maintained by absorbing the cars kinetic energy, effectively slowing it down faster but using zero gas?

[Even Steven]

Originally Posted by JCL12

To Clarify: you are saying that when you coast in drive, all fuel flow ceases and engine RPM is maintained by absorbing the cars kinetic energy, effectively slowing it down faster but using zero gas?

Yes, in a nutshell. It's not quite that simple, but the fact remains that a modern fuel management system has the ability to shut off the fuel pulse completely when a vehicle is coasting. Think of it this way--Why should the engine management system waste fuel by sending it to engine engine in a car coating down a hill? Fuel isn't required in such a situation, so it can simply be turned off. If you put the transmission into neutral while coasting, you are forcing the engine management system to start sending fuel to the engine to keep it idling. Therefore, it is more economical to leave the car in gear and coast down a hill instead of popping it into neutral and coasting down the hill.

Like I said earlier--do a little research and you'll learn all about it. I happened to learn this stuff in school

[spark00]

Originally Posted by Even Steven

Yes, in a nutshell. It's not quite that simple, but the fact remains that a modern fuel management system has the ability to shut off the fuel pulse completely when a vehicle is coasting. Think of it this way--Why should the engine management system waste fuel by sending it to engine engine in a car coating down a hill? Fuel isn't required in such a situation, so it can simply be turned off. If you put the transmission into neutral while coasting, you are forcing the engine management system to start sending fuel to the engine to keep it idling. Therefore, it is more economical to leave the car in gear and coast down a hill instead of popping it into neutral and coasting down the hill.

Like I said earlier--do a little research and you'll learn all about it. I happened to learn this stuff in school

This is interesting. Is this same for manual transmission also? I tend to leave my shift on neutral when I'm coasting to stop. I would like to save gas for environmental reason if I can. haha.

[Even Steven]

Originally Posted by spark00

This is interesting. Is this same for manual transmission also? I tend to leave my shift on neutral when I'm coasting to stop. I would like to save gas for environmental reason if I can. haha.

Yes, it works the same for manual trans cars too. I wouldn't be too concerned about putting it in neutral when coasting to a stop. The difference in fuel economy would be absolutely minimal. If you were always coasting down long hills in neutral or in gear, then you may notice a tiny difference in fuel economy, but even then it would be so small that it would be hard to accurately measure.

Either way, I'm sure that the differences would be hard to measure, but I was just trying to point out that coasting in neutral doesn't save gas....