DFCO (again) vs neutral

[davelobi]

Has there ever been a definitive answer on which provides better economy while coasting? Set engine-off neutral coasting aside for this one.
Picture a long down hill. I can coast further (and a little faster) in neutral with engine idling than I can in gear with car jumping into dfco mode. It's a no brainer until you factor in that neutral (idling) coasting is still consuming a bit of fuel. I love playing with all three but wondered if anyone had thoughts on these two methods.

[CigaR007]

Very case specific since I have a hybrid vehicle, but I favor DFCO in shorter and steeper downhills to top off the HV battery pack. If battery pack reaches 75% SOC, I switch to Neutral coast down.

Always engine ON neutral coasting in long and sustained downhills, in my case.

[davelobi]

Originally Posted by CigaR007

Very case specific since I have a hybrid vehicle, but I favor DFCO in shorter and steeper downhills to top off the HV battery pack. If battery pack reaches 75% SOC, I switch to Neutral coast down.

Always engine ON neutral coasting in long and sustained downhills, in my case.

Ooh, I hadn't thought about hybrid cars because I've never owned one. Re-gen is an obvious plus for you.

Ok, hybrid vehicles aside, now what say you?

[redpoint5]

Don't have any evidence, but I'm thinking it comes out nearly even. You maintain more speed in neutral and therefore get a slightly longer overall coast.

I mostly N coast. There's a 2.2 section of road on the way to my parents house that if I can hit 75 MPH and then shift to N, I'll make it all the way to their house. DFCO makes me lose too much speed to maintain a coast up minor hills along the way.

[davelobi]

I suppose there are too many variables. Each coasting opportunity is unique in length, decline, etc. Each vehicle has different glide ratios in dfco. Rolling resistance, etc.
All I know for sure is that my wife hates riding with me when I'm working on a good tank. I corner way too fast, drive too slow, never use my brakes, etc. Then I jump on my truck and ruin the planet.

[davelobi]

I just saw this thread in "drivers ed"
https://ecomodder.com/forum/showthre...fco-41189.html
Kinda the same topic but I wasn't courteous enough to check around first. Just thought about dfco today on a long coast and hadn't posted on here in a few years.

[Gasoline Fumes]

Engine off in neutral is the true winner, but I'll use all three at different times. DFCO if I need to slow down or control speed, and idling in neutral if I'm trying to keep the heater output up in really cold weather.

Since idle consumption is fairly consistent, the faster you're going, the better idling in neutral gets. DFCO might be better at lower speeds. Drive a consistent route and have a way to measure trip MPG? Try both ways!

[davelobi]

Originally Posted by Gasoline Fumes

Since idle consumption is fairly consistent, the faster you're going, the better idling in neutral gets. DFCO might be better at lower speeds. Drive a consistent route and have a way to measure trip MPG? Try both ways!

Back in the day with the saturn I clipped a listening device (chassis ear) to one of the injectors so I could hear when it was clicking and when it fell silent. After a while I could feel when it went in and out of dfco. Was searching but never did find the actual parameters programed in that were required to allow dfco. Engine temp has to be some minimum, closed loop, minimum speed etc. At slow speeds for example it would fall out of dfco as not to stall.

Last summer I had a little 4cyl stick Tacoma and was in the middle of a really good mileage tank. Wife wanted to take it to the store so I said sure, knowing it was going to kill my likely pb on it. I was literally on the front porch with a coffee when she left. She started it and then just sat there playing on her phone or something. It was an excruciatingly long minute of idling but I fought off the urge to say something.

[Ecky]

If you need to coast to a stop (say, a stop sign), the best way to reach there is burning zero fuel, so either DFCO or engine-off coasting in neutral would be equal. Coasting in neutral while idling will burn more fuel.

If you're trying to conserve momentum, look at it in terms of cumulative pumping losses. If you DFCO, you have the cumulative pumping losses of the engine turning at whatever your cruising RPM is, being subtracted from your momentum. If you put it in neutral and idle, you have the cumulative pumping losses of idle RPM, but instead of them being subtracted from your momentum, the engine burns a bit of fuel. Shutting the engine off means zero pumping losses. Overall idle is a net win.

If you need to coast downhill and you need to bleed speed (e.g. speeding ticket risk), DFCO bleeds more speed and you burn zero fuel while doing it.