I was running a test today to find out if I was better off gliding in N or gliding in D. 88HF mentioned that I might have fuel injector shutoff so D might be more efficient. Coasting from 35mph to 25mph in D I was using 2.5 LPH. Same speed in N was using 2.0 LPH. So in N I'm using .5 Liter less.
FYI, the scangauge might not be in a position to determine that fuel cutoff has occured. You might need to put a probe on an injector lead to know for sure (or find someone who has model specific info). Monitoring the loop status might provide a clue, but nothing conclusive.
It's a little complicated. When each manufacturer wrote the software for each models in-car computer, they made different assumptions and otherwise created different behaviors. There is no guarantee that it is accurate without actually looking at the signal being sent to the injector (or knowing something about your cars computer).
The computer senses higher RPM, might be sending one thing to the obd port and doing another thing with the injector.
Whether it cuts off fuel is one thing - and certainly important.
Whether the engine rpms drop is another question, and also important.
If engine rpms stay steady that shows the transmission is "driving" the engine; that will make your coast lose speed faster.
In your case you are able to see gph so of course that rolls up all the information into one nuber.
I recently drove a Ford Edge awd, automatic. Coasting in N gave exactly the same rpms as coasting in D. Go figure.
In my own car, coasting in N gives about 800 rpm vs. about 1500 rpm in D. As it's an '89 I doubt it has fuel cutoff. ymmv, as usual.
Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.
My wife's transportation is a T&C with a 3.8L engine. My impression is that Chrysler, as well as everyone else, is doing something with the engine speed, when you let off of the gas. My impression is that they let the rpm drop a little, but not the same as if you had complete control from the gas pedal. The resulting feeling is that the car will coast further in gear, than it would naturally and that feeling makes people feel the engine and transmission seem to be more efficient.
I did some neutral coasting and I think it helped, but I don't have any instant feedback, like you have, so I appreciate the information. I don't care if the injectors shut off, or not, I just am trying to get it to get as good a mileage, as I can.
I get further coasts while in Neutral compared to Drive. It seems that the engine braking would cause this but I'm not an expert. Myself and 88HF ran a simple test. 65-55 from in N netted 30mpg, 65-55 in D netted 28mpg, while 60mph sustained netted 26mpg according to the SG2. This test wasn't scientific so the numbers could be fudged.
Gary, you can test it with your speedometer. Something as simple as coasting down your street from point X at speed a and then at point Y see what speed B is down to. Try it in D, try it in N... maybe 3 times or more each way. That'll tell you...