The engine has to do a little more work to push against the torque converter compared to if you're in netural. If you've got approximately the same RPM either way, then it's feeding a little more fuel in.
I've setup a fuel rate gauge (see the "realtime monitoring for pre-obd2 cars" thread), and the difference in my 2002 GMC is miniscule but definitely there.
On my Odyssey V6, it idles at about .05 gph in gear, and in neutral it flips back and forth between .04 and .05. The resolution is really rough with numbers that low, but at least it shows that neutral uses less fuel.
Noticed something today on Marvin, he has a 3 speed hydraulic torqueflite derived transaxle....
Below 2000 rpm, if I put it into neutral for a second or two, then put it back in drive it appears not to engage drive until I press the gas again... thus you can be "neutral coasting" while still having instant access to acceleration should you require it... it appears to stay out even when you brake to a stop, and only engage when you touch the gas again. It does seem however to go back into drive fully when over 2000 rpm, guess that's because the tranny can still push the engine. Seems to need a certain amount of push from either side to engage, and lacking that stays out.
However, I think I remember one time a while back, I shifted into N, then went back to D and coasted down to a stop without brake use... and it sat there 5-10 seconds and then engaged drive slowly and began to crawl again. I didn't make any connections then about it staying in N though.
I remember The RoadWarrior..To understand who he was, you have to go back to another time..the world was powered by the black fuel & the desert sprouted great cities..Gone now, swept away..two mighty warrior tribes went to war & touched off a blaze which engulfed them all. Without fuel, they were nothing..thundering machines sputtered & stopped..Only those mobile enough to scavenge, brutal enough to pillage would survive. The gangs took over the highways, ready to wage war for a tank of juice
P&G (using N but not EOC) definitely works in an automatic. Proof is in the latest gaslog entry for my truck. I haven't gotten this kind of mileage in years, since the truck was brand new and I was driving 100% highway with the cruise control at 65. 18.31mpg!!!
I've been pulsing at 2000 to 2500 rpm, using as much throttle as I can while staying in third or fourth gear. It may not be as good as if it was manual, but it's sure better than nothing.
I've noticed on my '05 Passat that if I use the cruise control going over hills that it holds a higher gear longer than if I try to drive it myself. I even tried putting it in tip-tronic mode to hold top gear but the computer makes it down shift. I have been having lots of fun with coasting in N on the downhills. It does not seem to be making a big difference in my FE though.
jcp123- A newer tranny with OD and lockup would probably give your Mustang great highway mileage.
You might try gradual acceleration downhill and then coast in N going uphill. You just need to accelerate enough to get about 5 or so over the speed limit and then coast to about 10 under the speed limit if you can.
I have tried this with great success. It takes some experience to fine tune the driving style and when to accelerate and coast but is well worth it. If you had a ScanGuage, you would probably learn on this faster than I have (haven't been willing to shell out the money for a SGII yet).
You can look at my Gaslog chart and see the gradual improvements over the past few months with neutral coasting up hill. I am now seeing about 39 mpg when I started with only 32.
Scott, I'm curious why you chose pulsing downhill and gliding uphill. Is it because you can get a more useful pulse without causing a downshift?
In my truck I've been pulsing uphill and gliding downhill, just like I do in my manual transmission car. The theory is that the engine produces power more fuel-efficiently at higher loads, and that the wider throttle opening reduces pumping losses too. (Additionally, your speed is more steady, which helps with the difficulties of P&G.) However, with an automatic it's tough to achieve those advantages because it will downshift. My strategy has been working for me, but maybe I'll try yours too, to see if it works even better.
I actually picked this tip up from PaleMelanesian and an article that he had forwarded to me.
I am not as technically adept as you on the shifting details of my auto trans (I am just a marketing guy) but I think the basic concept is to accelerate downhill and use the advantage of gravity to help multiply my speed acceleration while using as little gas as possible to reach speed. Then I coast uphill in neutral with my engine idling at 700 - 800 RPM. The more I can avoid using the gas uphill, the better off my FE.
Now, I can't always coast all the way uphill in Neutral so I sometimes have to shift into drive and maintain my slowest speed through the rest of the slope (usually around 55 mph or so on the highway).
I am sure there is a lot more science behind this technique that I am not totally aware of. I will let PaleMelanesian weigh in on more details on this technique if he chooses too. All I can tell you is that I saw an immediate 2 mpg increase in my fuel efficiency when I shifted from coasting in Neutral downhill to this technique. I can't guarantee that it works equally well for all vehicles but it sure works for my 2000 Civic Coupe.