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Old 05-15-2009, 11:25 AM   #19 (permalink)
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The Crimson Crawler - '04 Hyundai Elantra GLS
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Originally Posted by 99metro View Post
Just my opinion...

I have heard lots said about fuel cutoff when in gear and the throttle off. I have a hard time believing that the fuel is stopped completely. This would mean the engine is rotating with just the spark plugs firing.
It stops ignition too. My car will DFCO. The RPM's go up when I drop a gear, and then there is a little "blip" and at the same speed, they drop by about 300 RPM. Once it's down to ~11 RPM, the tach suddenly freefalls to about 400, and then bounces back up to 1400 or so.
Originally Posted by jimepting View Post
Incidently, neutral engine-on coasting probably delivers worse FE than engine-on coasting in gear on most modern cars. As mentioned earlier lots of newer cars will go into fuel cut-off when deaccelerating in gear. Go to neutral and you are stuck with engine idle consumption if the engine is on.
DFCO does produce better mileage in the short run...but that's the thing. It's SHORT. Glides at least for me are about 1/3 to 1/5 as long as coasting in neutral. So yes, I'm getting 9999 MPG when in DFCO, but only for say 200 feet, instead of something like 150 MPG for 1000 feet.

I hope that clears some things up?
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