Cost to Coast
 

Hi,

I just heard about Hypermiling yesterday. I had no idea! I thought I had no options in getting better MPG but now I see a few good techniques. My question is on the Pulse and Glide thang...

I have a 1997 Civic automatic transmission.
What is the difference (in gas savings) between P&G in neutral with the car being on & off? I ask because I'd rather not turn the car off while I'm driving. just because it's a pain. Does the car have to be turned off to get better gas mileage using P&G? Or will being in Neutral save gas?

thanks!

HHINLA

Depending on what your speed and idle fuel consumption are coasting in neutral may save gas. If the engine is at a high enough load, it probably won't. It really depends on the situation. Determining how much load is on the engine during a portion of your trip is the best way to accurately figure out whether or not popping in/out of gear is worthwhile in terms of fuel savings.

^ he's smart.

Get some instrumentation and see for yourself, though, :). It'll be worth it.

Welcome to EM!

In my 4 cyl GMC if I coast in neutral with the engine running it is burning 1.2 ounces of gasoline per minute. With the engine off it is of course not burning any.

So it would take less than 2 hours of coasting in neutral, with engine running, to burn a gallon of fuel.

If I coast down hill, in gear, such that the engine is braking the vehicle, it burns no fuel. But if I coast down the same hill in neutral, using the brakes to slow the vehicle, it is again burning 1.2 ounces of gasoline per minute. So it is much better to have it in gear than in neutral while coasting down hill, if I need to slow the vehicle.

You'll really want to check your owners manual before doing any engine off coasting with an automatic transmission. If your manual says your car can be flat towed you are okay to engine off. If it says you can't flat tow, its likely you will damage your tranny over time due to lack of lubrication and pumps not running.

The benefit of engine off is definitly there. If you do a search its been asked a few times and there are some good answers out there. How big a difference really comes down to how much fuel your engine uses at idle. Larger engines will use more. Older and inefficient engines will use more. My Paseo's 1.5L (in current modified state) uses more fuel idling than my Matrix's stock 1.8L engine. Instrumentation is the only way to know this.

Ok, sounds reasonable. What is the best instrumentation to get? Will ScanGuage tabulate the engine load? I'm not a super technical person but I'm willing to spend some time and money on this stuff. I read some great info on making the car more aerodynamic. I think I'll do that as well. Thanks for the comments!

HHINLA

Engine Load at stop
 

Hi,

Just got my ScanGuage II and I've been messing around with it. I haven't tested Engine Load in Neutral while moving yet. But, I have done a little testing while at stop lights. It seems the Engine load is slightly greater when In D4 at a stop rather than put in Neutral. I get around 34 LOD in drive and around 30 LOD in neutral stopped. I'm wondering if that will make any difference with the MPG or if it's not even worth it.

I'll do some tests with LOD while in neutral while I'm coasting next week. Though I have an automatic which switches off the fuel injector while in coast anyway. If this is the case maybe it wouldn't make any difference?

HHINLA

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.

I'm curious and my van can't have a scanguage:(

I'm running on deep cycle batteries to eliminate these drains. I have not done the testing to see how much benefit I get but MetroMPG has http://ecomodder.com/forum/showthrea...n-70-a-98.html

Good luck.

Watch the gph gauge in D and in neutral. gallons per hour. In the automatics I've checked, neutral does indeed use less.

Aha! Thanks for the tip! I'll report back.

HHINLA

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. :D

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

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

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.

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.

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...

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.

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...

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.

That's basically what I saw today.

If I got off the gas completely, in 5th gear, above 32mph, the MPGuino would go to 0.00GPH ahd the scangauge would go into open loop. the fuel would start flowing again once it slowed down to 32mph and closed loop would be indicated.

It also seems to show "open loop" if I even look at the gas pedal the wrong way while accelerating :) But there is not a significant jump in consumption between just below open loop and just above open loop. I guess I have to hook up the cheesey o2 monitor to see if the car computer is still checking the mixture or not.

But if I account for all that, and relight the engine with the throttle at an appropriate cruise condition (not decelerating, not over accelrating), it goes back to indicating closed loop within 2 seconds.

Yes, I'm also very skeptical about that. The only difference I can tell between glide in D or N is that in N you can go a lot farther. Even if indeed the engine is using no gas in D glide I'm going to change to N just because of how much farther it glides. Seems like at least twice the distance!!!

HHINLA