I'm trying to figure out which will yield the best gas mileage at 45 mph: coasting in Neutral at idle speed (550 RPM) or decelerating in Drive @ 1300 RPM?

I've heard at idle speed you're at a lower RPM but using more gas. I've also heard when decelerating, your injectors practically shut off, yielding better mileage although at a higher RPM.

Could a few of you tuners shine a little light on this for me?

 

Taking the truck out of gear while moving is not a good idea.


my 2 centavos

 

There is a parameter called DFCO, deceleration fuel cut off. Once you let off the gas(in gear), wait a few seconds and you can usually tell when it is enabled. When DFCO is enabled you are getting great mpg.

 

2 vague. Trever, what is the downside as why it's bad? I've done this.

 

Less controll of the vehicle.



don't do it again Tom....

 

Coasting for sure!

 

You definitely are going to coast further than decelerating in gear due to reduced drag but it is more practical to modify the DFCO settings to maximize fuel economy.

 

Its hard to modifiy the DFCO becuase when decelerating with it on the torque converter will unlock then the engine rpms drop to where the DFCO disengauges then sometimes DFCO cuts on again. Then theres wierd delays and anoying shuttering and popping noises.

 

The wear and tear of taking the vehicle out of gear with an auto transmission will cost WAY more that a couple of sips of gas. Putting an auto in neutral varies the fluid pressure, wears the clutches (or band, depending on what gear it's in), and putting it back in gear creates more heat, among other issues (planetary gearset wear to name one).

If it's a manual, I doubt the mileage affliction will be measurable. I tend to coast to a stop because I'm too lazy to keep my foot on the clutch all the time in Atlanta traffic. It's doesn't hurt anything to pull a synchronized manual transmission of gear though.

 

I've never heard of DFCO before.

I've been able to increase my gas mileage by dropping it from OD to N when coasting to a stop. I've done it on the highway before also when closing in a a slower moving vehicle ahead.

There is no loss of control other than not being able to accelerate. The engine doesn't shut off, the RPM just drop to 500.