Cost to Coast

[HondaHound]

Originally Posted by orange4boy

Hondahound,

Something you might want to try is the engine load at idle with all accessories off then try it with blower fan, defrost, low beams highbeams, turnsignals, brake lights etc. This may give you an indication of alternator load and how that affects idle and driving fuel consumption. To check residual load you could unplug your alternator.

Ok, I'll try that this weekend. But, I think I'll pass on unplugging the alternator. I'm not really a car guy so finding it, unplugging it, (even though it's probably easy) is not something I want to do. I'll keep my hands clean on this one.

[HondaHound]

Just checked it over the weekend and my car does use less gas in neutral than D at idle. I got around .21 gph in drive and around .19gph in neutral. Not a huge difference but it seems to me it's worth it because I do a lot of city driving.

Also, I'm not even going to try neutral coast with my automatic. The fuel injector turns off when I coast and claims that I'm not using any gas in this stage. I get 0.0 gph when I do this. I don't know if it's really using no gas at that point but I don't know if there would be a way to test it with the gauge if it was.

HHINLA

[PaleMelanesian]

Bring up the Loop gauge. If it shows Open Loop in that case, you are indeed using no fuel. (DFCO - decelleration Fuel Cut Off)

There's a time for that, and there's a time for coasting in neutral. DFCO trades zero fuel usage for a shorter glide distance. You have to weight the situation to see what's best. Generally, it's better to coast in neutral, because of the longer glide distance. If you're having to stop anyway, use DFCO.

[HondaHound]

Originally Posted by PaleMelanesian

Bring up the Loop gauge. If it shows Open Loop in that case, you are indeed using no fuel. (DFCO - decelleration Fuel Cut Off)

There's a time for that, and there's a time for coasting in neutral. DFCO trades zero fuel usage for a shorter glide distance. You have to weight the situation to see what's best. Generally, it's better to coast in neutral, because of the longer glide distance. If you're having to stop anyway, use DFCO.

Who knew all this stuff? Thanks for all the tips! What I've found out is that indeed my car does read "OPEN LP" when in coast. But, when I shift to Neutral while coasting it goes into "CLSD LP" and the GPH guage starts to take readings again. That seems sort of strange. That would mean that all of a sudden the car is using fuel again even though I just went from D in N.

HHINLA

[Ford Man]

DFCO only works while the car is in gear at a certain rpm range. I don't completely understand it all, but I do know this much. Once the rpm's get so low then it starts to burn fuel again that is why you benefit from putting the car in nuetral while stopped, because with the car out of gear it's placing less load on the engine. You know there is load on the engine of an automatic stopped in gear, because if you let off the brake the car will slowly take off on it's own, but in nuetral it will just sit there with the brake off.

[Clev]

P&G definitely works with engine-on coasting. My record so far was 39.7 mpg in my Saturn Ion (5 speed, 30 mpg fwy rated), and this weekend, I rented a Malibu (4 speed auto, 29 mpg fwy rated) and averaged 35 mpg in mixed city/hwy driving. Both done with engines on at all times except in the drive-thru.

[dcb]

Originally Posted by PaleMelanesian

Bring up the Loop gauge. If it shows Open Loop in that case, you are indeed using no fuel.

You know, I'm not convinced that open loop indicates complete fuel shutdown. I thought I saw on the metro (with the mpguino ) that the injectors were still firing even when in overrun at a fairly high speed. I think I need to do some more tests on that...

[PaleMelanesian]

Please do some testing. We could all gain from it. I know some cars don't do DFCO at all, and some have some crazy conditions that must be met. (> 40mph in one case)

I have the older version of the Scangauge, that doesn't calculate fuel cut correctly. So I just don't. EOC all the way. I just have to start that much sooner so I don't need any braking.

[99metro]

With my other 3 automatics (2 Full Size Broncos, F250 Diesel), I can pulse and glide (40 to 55, then back down) by shifting to neutral, then at 40, shift to drive, repeat. I also neutral coast A LOT. Between my wife and I, we found good results from 55 mph, to coast down to 25mph before touching brakes at the stop sign. I'm sure others will go much lower than that. It takes some timing to find where to shift to neutral to be down to 25 or so coasting to a stop sign.

Neutral-coasting these gas guzzlers has netted the most FE gain. Unless your car coasts forever in Drive, you should really reconsider neutral-coasting with the engine ON. Watch the Scangauge and see what it does for you.

That Scangauge you got will teach you lots at where you can improve your MPG - enjoy!


PS Also you ought to consider adopting a self-imposed 55 mph speed limit...

[Clev]

Originally Posted by dcb

You know, I'm not convinced that open loop indicates complete fuel shutdown. I thought I saw on the metro (with the mpguino ) that the injectors were still firing even when in overrun at a fairly high speed. I think I need to do some more tests on that...

No. If it's 'open loop' in the engine-computer sense, it indicates that the engine is running a fixed (usually slightly rich) mixture, rather than relying on oxygen sensors and such. The engine usually runs open loop during cold start, since the oxygen sensors need to warm up before they begin to work. It could be that the computer goes into open loop BECAUSE it's cutting off fuel, but 'open loop' by itself actually means that the engine is running slightly richer than it should.