i talked to my friend about this, and he referenced me a road and track question/answer regarding fuel injector operation during deceleration/coasting:

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Quote:
You're correct about electronic fuel injectors being on or off devices. What you suspect is also true; during deceleration the injectors simply aren't opened. This leads to infinitely high "instant" mileage readouts, as you've seen.

The injectors are reactivated when engine approaches idle speed so the engine won't stall.

click here for the full q&a
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this means, during deceleration or braking the engine uses no gas if rpms are not near idle speed (~700 rpm). at 40 mph my rpms are around 1400, double that. thus i don't think FAS would help me save any more gas in the scenario i described previously.

 

That would be an incredible spot for an FAS every day...4 miles...I'm jealous! If traffic conditions put you into disease, then the least I can say is you should be sliding into Neutral every time you hit this stretch. It won't be infinite MPGs for free like an FAS, but you will see dramatic decrease in RPMs, probably 1.3 or 1.5 down to 0.7 or 0.8 (close to half at times) and that will yield even better results than you're currently getting. True, you're seeing 120+ MPG and it may be as high as 150 MPG, but in Neutral you're more likely at 150-170 MPG, and FAS is immeasurable, it's free, it's GRRRRRREAT!

 

Many years ago my wife parked her car in the garage with the transmission in Drive and got out. Even though the ground was level, the car rolled back out, then went down the driveway and smacked into a parked car across the street. Ever since then, she religiously sets the parking brake immediately after turning off the ignition!

Fortunately, on the '05 HCH you can't take the key out of the ignition unless the transmission is in Park. (I just tried it.)

 

helterskelter-

i just tried FAS today, on a 3.1 mile long (sorry, 4 was an exaggeration), very gentle descent - thanks so much tbaleno and pzev and everybody who supplied all these informational posts - helped me greatly. Using FAS for those three miles instead of coasting in gear boosted my mileage 4.2 mpg, which is a lot for a measly three miles.

route picture:

 

What about coasting in neutral? Isn't that what started this whole discussion? That's what I really want to compare - neutral coasting vs FAS coasting. How did you calculate the 4 mpg? How many miles were on the tank when the change was observed?

In any case, I think even at 4 mpg, the whole time pegged at 120+ mpg, I really don't think that 3% is going to make much difference. Certainly not enough for me to risk the safety issue of a FAS.

 

Awesome! That's a HUGE difference! Isn't that such a great feeling when you're flying down the road with NO engine?

 

My ICE actually STOPS, then restarts a moment later!

 

On the 20 mile daily route I usually take, my gauge consistently reads 52.0 mpg by the end of that section mapped below. With FAS, the gauge read 56.0 mpg. 20 miles were on the tripmeter for each trip.

I think you are referring to Auto-stop, when the car turns off the engine at stoplights. I'm referring to closing the fuel injectors during deceleration, which I believe somebody refuted by saying that if the 03-05 HCH ICE is ever running, it is using some gas, unlike on the 06 HCH ev-mode.