I don't know if this has any truth behind it. Maybe someone could test it out with their fancy computers or something.

On the manual transmissions do we have a fuel shutoff valve that shuts off fuel when its not needed. When decelerating, instead of pushing in the clutch and idling at 800RPMs with a fuel flow of X, if you leave it in gear, does the engine cut off ALL fuel to the engine because it is not needed. better to burn nothing than an idle amount.

I did this by leaving it in 6th when decelerating until it hit 1000rpms. I averaged about .5 a gallon more than normal... I tried not to change my driving habits but who knows.

Any thoughts???

 

If it cut off fuel the engine would shut off. I know a Prius does this, but a g35 does not.

 

^^+1 Agreed. RPM's mean combustion, which means gas is being used. There's no shut off valve for cars during operation, unless it's a hybrid when it's using battery power only.

 

No our cars do not have that, but you can save lots of gas by doing some of these things. Not all may be lagal.
1. Accelerate then shut car off and coast in nuetral
2. Remove side mirrors
3. Shut car off on downhills
4. inflate tires to correct pressure
5. shut car off at stop lights
6. empty trunk of junk to include spare tire
7. Proper tuned car is a necessity
8. Last but not least, drive slowly or less than 60MPH
9. They all work, then again if that's what you were after, why the heck did you buy a G35???????????????????

 

With any tranny and in most any fuel injected car, when you take your foot off the gas and have the car in gear (ie engine braking), the injectors are not firing (ie no fuel is being consumed).

 

That's a new one to me. I was of the assumption if the car is on you're burning fuel. If there's something I don't know please inform me

 

http://en.allexperts.com/q/Automotiv...ne-Braking.htm

 

i kind of think that by down shifting the wheels/transmission is driving the engine, not combustion. So why would fuel need to be in there. I read on another forum that most new Japanese and German cars do this. Does it need a little for lubrication? Not that I would do it, but what would happen if the engine was shut off at 60 mph in sixth gear. Do you think you would decelerate faster?

 

Thanks for the info DaveB. Well this report that I saw on the news reported all the things that I listed and showed a significant increase in MPG. I just can't remember what brand car it.I can assure you however it wasn't a hybrid or anything like that, it was just a normal 4 bangger. They did however include that fact that some of the methods the guy used could be illegal in some states.

 

Our car does indeed cut off the fuel if the rpms are over the idle rpm. And yes, the engine is "off" in this case, and that's fine, because the car is powered (a/c, steering assist, etc) by belts off the crankshaft, which is still turning w/ the rear wheels.

I can't find it but I believe someone quoted something in the service manual. You can prove this yourself if your car features the MPG screen by coasting at say.. 20mph w/ the realtime monitor on. If you coast in N, you will get something like 25mpg.. if you coast in gear, you will get "infinite" mpg -- that is, your mpg meter will be pegged.

 

Theoretically, NO, you would actually decelerate slower. If you leave the car on, and drop to say 3rd gear @ 60 (could probably even hit 2nd if you rev-match correctly), you're using compression and the weight of the car against the motor to slow you down; this is called transmission braking (read, "braking", not breaking). If the car were shutoff and in neutral (READ: PUT IT IN NEUTRAL BEFORE YOU SHUTOFF THE CAR!!!) you're basically just rolling with nothing more than wind resistance and tire friction to slow you down. Make sense?

 

If the car were shut off and in neutral while moving please be aware that you will not have any power steering or power brake assist. That's a potentially dangerous situation.

 

+ 1

 

The problem with no power steering for most people is that the steering is too loose.

You do still have vaccuum built up for 1 or maybe 2 stops, even after you turn the car off.

 

IMHO as I've not risked my life to try:

1) No power steering = steering WAY stiff. It would be an easy matter of gearing to make a too easy steering stiff and eliminate the PS all together

2)From my old cars, no vacuum signal from the engine = no power brakes. Okay going down a hill would = one having to stand on the brakes as much as possible. The brake booster doens't "store" vacuum as far as I know.

If manual, it's an easy thing to try. Park car on hill, put it in neutral and try to stop the car. With an auto, if you can turn the ign off in neutral, that might work.