Neutral at speed
 

In my ending quest to get the best mileage possible, I've dropped the tranny into neutral a few times going downhill and noticed that the engine RPMs are hovering around 1500, I would have thought it would drop to idle rpms.
Wondering if dropping in neutral actually aids in trying to improve mpg or just leave it in gear.

If you leave it in gear and get all the way off the gas, the engine goes into DFCO mode (Deceleration Fuel Cut Off). Basically, it turns the injectors off completely as long as it knows the transmission will keep the engine above running speeds. Cars have been doing this for at least 20 years.

Putting it in neutral forces the computer to keep the engine running on its own, thereby using more fuel.

In Europe, some of the small cars actually kill the engine completely when coasting or at a dead stop. We rented a Mercedes B Class (not available in the US) with a standard transmission. It would kill the motor every time you put the stick in neutral and let off the clutch, and automatically restart it as soon as you push in the clutch to put it in gear. And yes, I tested it to see if I was faster than it could react and I wasn't.

As for the idle speed, it's like the rev limiter. It has different settings based on a myriad of inputs. Put your truck in neutral and floor it. You'll find that the rev limiter is much lower than it is in gear. Same thing with the idle speed.

To maximize mileage, concentrate on coasting as much as possible and it'll net some gains.

Is not the 3.5gdi engine in fact a lean burn engine, where at off throttle there is more air and less fuel involved when coasting?
I have been doing some searching on this topic. As with my torque app i have noticed the afr readings pretty high when off throttle coasting.
Someone with some knowledge chime in

Not necessarily, it depends on the situation. I put mine in neutral on downhills where it can maintain speed. If I leave it in gear, the engine drags the speed down and I have to stay in the throttle to maintain a safe speed.

The dfco is causing those readings. The injectors are closed while coasting if certain parameters are met. See above. And I haven't seen any evidence the eb is a lean burn engine.

I don't think I understand what you're getting at here.

I think he is talking about engine brake or when the transmission downshifts to slow you down as you are coasting down hill. I could be wrong though.

Nah I got that part.

- Coasting in neutral: injectors on and burning fuel.
- Coasting in gear: injectors off and not burning fuel.
- Coasting in gear but applying some throttle: injectors on and burning fuel.

Simple as that.

Lol...if it turned the injectors off completely...would not the engine stall ??
no gas...no fire

So how much mileage are you trying to gain by going through this effort?