among other things it'll depend on the rpms involved. dfco doesn't engage in most cars till 1800-2k rpm. unless you get the revs that high in 5th neutral will use less gas.
1991 Toyota Pickup 22R-E 2.4 I4/5 speed
1990 Toyota Cressida 7M-GE 3.0 I6/5-speed manual
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Your Cobalt with electric steering and manual transmission would be an ideal car for Engine-Off Coasting. As mentioned above, such a technique raises concerns with safety, other drivers, and traffic; also it raises legal questions. It should only be done by drivers who are 100% comfortable with it, and only where legal. Is it something you'd be interested in learning about?
this raises a question for me thats been buggin me: how would one know that you are in fact neutral coasting. it IS illegal in IL to be coasting down hill with the engine running mind you and the vehicle in neutral. BUT how the hell can anyone know if your in gear or not with a manual tranny?
I have yet to figure out how anyone would know. Even if you were in an accident, I'm sure plenty of cars pop out of gear when the car flexes in a collision. Of course, if you're dumb enough to say "but I was just coasting in neutral, I wasn't trying to go fast" when you get pulled over for speeding....
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Remember when coasting in neutral with the engine running - the faster you coast the higher the mileage reading.
I find that even keeping it in gear at moderate speeds and having it slow a little really pumps up the average mileage because of the DFCO which works in my xB down to less than 1000rpm when the engine is warmed up. Driving out to the Cape, my trip mileage jumped up quite a bit more than I expected when I DFCO down the back side of the Bourne Bridge in gear. Apparently 9999mpg really adds a lot to the average.
I've been using fuel cut on del. since I heard that leaving it in gear gets better mileage. I did some research on ALLDATA on my car and when the tps% goes to 0 and the rpms are above like 800-900 the injectors cut off for emissions and economy.
Using it in different situations, mileage hasn't really greatly improved or declined but what I have noticed is that when you let off the throttle really rapidly its pretty harsh. espically when I feather the throttle and I get really close to 0% throttle. ( where I should probably ether speed up or throw it in neutral). Another thing, my front mount is practically gone! 89 civic.
I just thought about how the older civics have that dashpot that stops the throttle from closing to fast. that would technically reduce mileage cause the injectors would shut off later, but it would make the transition to fuel cut off a lot smoother.
The data for newer civic's is the same. at 0% throttle above 800-1000rpm the injectors cut off. and they don't have a dashpot and the front lower driver side mounts are always bad.