Neutral at stop lights, save gas??

[CO ZX2]

Originally Posted by rh77

My SG does the same thing, but what it doesn't know is that the injectors actually cut fuel while coasting in D (so it should read 9999).

Several vehicles benefit from Neutral idling -- the GPH arguement is quite valid. For maximum efficiency, long idling situations should be in engine-off mode (like at traditionally long lights, etc).

BUT...

The TSX, for example, has variable cam timing (i-VTEC) that cuts the cam timing dramatically at idle and uses very little fuel. It actually uses more fuel to shut-down and re-start if you're not sitting for at least 2-minutes (according to the on-board FE recorder). I don't use neutral idle anymore in the 'Teg either, as I'm worried about the longivity of the transmission going from N to D at a stop (a bit of a hard engagement). Coasting in engine-off N, starting up, and back to D with a rev-match seems to work well, tho...

RH77

It doesn't appear to me that you guys are differentiating well between coasting with engine on and engine off. When you are coasting with engine off NO fuel is being consumed. So how can your fuel consumption be less than that? Coasting in gear only slows your car down faster, how can that be good? If there was total fuel cut at any time with any car, the engine would die. Engine Off Coasting is a sure fire way to substantially raise your FE. It worked for me and has worked for many others.

[Ted Hart]

Originally Posted by budomove

According to Ben (SVOboy) the fuel injectors on hondas turn off while coasting in gear, so the same goes for us.

Turn off the fuel injectors, and the engine will die! Will it not? Does it restart itself, too? I'm confused....

[omgwtfbyobbq]

All modern FI cars should have the injectors turn off (or maybe pulse depending on the post cat O2 reading) above a certain rpm with no throttle, depending on coolant temps (maybe other things too?), when the vehicle is above a certain rpm in any gear. Once the engine drops below a certain rpm, the car starts "idling" again, in or out of gear. I suppose manufacturers could tie the transmission switch into the vehicle idle, but the problem with this is if the switch goes, the car can stall at stops.

[ELF]

Originally Posted by Ted Hart

Turn off the fuel injectors, and the engine will die! Will it not? Does it restart itself, too? I'm confused....

If your speed is high enough the most auto trannys will spin the motor if you shut it off, So at higher speeds cutting fuel would not kill the engine.But once you get to a lower speed the tranny will stop turning the motor and engine will kill.

[CO ZX2]

Originally Posted by ELF

If your speed is high enough the most auto trannys will spin the motor if you shut it off, So at higher speeds cutting fuel would not kill the engine.But once you get to a lower speed the tranny will stop turning the motor and engine will kill.

ELF. You are wrong on this one. If the fuel is shut off the engine is killed, not running under it's own power. Even though the engine is turning, it is being powered through the transmission, transmission being powered by the wheels. This scenario results in reverse FE. You are using energy you have already generated to turn over a dead engine. Not that hard to understand. Does this make any sense to you??

[SVOboy]

Originally Posted by CO ZX2

ELF. You are wrong on this one. If the fuel is shut off the engine is killed, not running under it's own power. Even though the engine is turning, it is being powered through the transmission, transmission being powered by the wheels. This scenario results in reverse FE. You are using energy you have already generated to turn over a dead engine. Not that hard to understand. Does this make any sense to you??

Coasting in gear doesn't have to equal reverse FE. You can coast to stops or in locations where it would be advantageous to have the resistance to keep you from going 90 down the hill and dying.

Ted, the fuel is cut and the engine becomes an air pump as it is still connected to the wheels and rotated through that physical connection.

[Matt Timion]

Originally Posted by budomove

According to Ben (SVOboy) the fuel injectors on hondas turn off while coasting in gear, so the same goes for us.

I've found that to be true in my old honda (89) but not true in my new honda (2007)

[ELF]

Originally Posted by CO ZX2

ELF. You are wrong on this one. If the fuel is shut off the engine is killed, not running under it's own power. Even though the engine is turning, it is being powered through the transmission, transmission being powered by the wheels. This scenario results in reverse FE. You are using energy you have already generated to turn over a dead engine. Not that hard to understand. Does this make any sense to you??

I was only trying to explain to Ted that the engine would still be turning over at speed and not completely stopped, so it wouldn't have to restart. I didn't mean to imply the FE would be better.

[ELF]

[QUOTE=omgwtfbyobb If you have the time, could you check the fuel flow when coasting in N compared to decelerating in gear at a kinda slow speed, like ~40mph? If the idle consumption when decelerating is greater than coasting in N, then coasting must be a win win no matter what.[/QUOTE]

I checked today, hitting neutral at 40 mph....GPH was at .07 no throttle in drive.
switching to N at 40mph.. GPH went to 0.9 for about 2 seconds and then went back to .07

Seems to be no help going to neutral for coasting , at least in my car.

[repete86]

But at the same time though you're losing inertia energy because of engine braking. If you drop it into neutral, you'll coast longer, or at least that's the case with the cars I've owned.