engineermike

Lol at what? I've logged this a hundred times and even seen the tables governing it in ECM's dating back nearly 20 years. The engine would stall except that the transmission keeps it spinning. That's the point of all the parameters that must be met. . . to keep it from killing totally and having to restart.

If you are coasting, then you don't need power, gas, or fire.

acadianbob

I'll try a better explanation (I hope). There are numerous places where I can do a long coast if I put it in neutral. If I leave it in gear, the engine shuts the fuel off, and the truck slows down way before I want it to (or that is safe). Then I would have to stay in the throttle to make it. I would think that would use more fuel. An example is a long downhill with an exit ramp at the bottom of the hill. If I leave it in gear at the top of the hill, it slows way down and I don't make it to the ramp; so throttle is needed. If I put it in neutral, I easily make it all the way to the ramp without slowing dangerously.

So, I'm assuming that, even though I'm using fuel as it idles down the hill in neutral, I'm using less fuel than leaving it in gear and having to stay in the throttle. That's my theory and I'm stickin' to it! Does that make any sense?

I do agree that, if you are just coming generally to a stop, you should leave it in gear. You get the engine braking to save on the brakes and you get the fuel shut off.

I will often shift to "manual" and downshift the truck as I come to stops; especially higher speed stops like a freeway exit. Anyone else do that? I sometimes wonder if there are any long term effects on the tranny from doing that. What do you think?

engineermike

Makes sense now, but I don't think there is any appreciable difference between coasting in neutral vs coasting while lightly holding the throttle. Neither shut off the fuel and neither have any load on the engine. Since you can't take advantage of the DFCO in those situations, the only thing you could do that would be an improvement would be killing the motor and using the brakes, but there are safety and maintenance concerns with that. I do like my 3.15 rear gears because they coast in gear better, which maximizes the DFCO.

acadianbob

Yeah, any differences are likely to be unnoticeable.

greggebhardt

According to the mileage indicator I get BETTER milage slipping the vehicle out of drive when costing to a light or going downhill. Do not do it all the time but there are time when I anticipate a light way ahead and this works well.

Each to his own.

f150man3.5

According to my mileage indictacter i get max mpg's coasting in gear. And according to my torque app there is no fueling going on either, hence it shows high afr's while coasting in what engineermike calls "dfco"mode

f150man3.5

Further more. Coasting down hill, my truck will coast, it does not slow down as others have indictacted theirs do. I have 3.73 and i believe the 3.15's would coast better

techrep

iTrader: (1)

I understand the tranny will keep the pistons pumping and the plugs firing...but if you cut off the fuel...the engine die's and is no longer completing a combustion cycle.

engineermike

Yes, that's kinda the point. Please google this. It's quite well-known and not a new concept.

vteckiller2000

The engine is kept at the proper rpm it would be at in gear at the speed you are traveling, the point is to limit a jarring, possibly damaging shift back into gear while moving. Notice when rolling at speed and you put it back in gear from neutral, it was holding at the proper rpm for the cruising gear it would be in had it not been shifted into neutral.