I don't know if this has been discussed before but, I learned something today.
Until recently I never paid much attention to my GPH on the scan gauge.
So today I had it on and while at a stop light I checked to see how much fuel I was using, 0.3 GPH in gear. I put the tranny in N and the GPH changed to 0.2

So at least in my car I can save some gas by using neutral at stop lights. Don't think I'll be saving a lot but every little bit helps.

Awesome info, I've been meaning to ask about this. Imo it means that no matter what, coasting in N should result in better mileage. I think. If you have the time, could you check the fuel flow when coasting in N compared to decelerating in gear at a kinda slow speed, like ~40mph? If the idle consumption when decelerating is greater than coasting in N, then coasting must be a win win no matter what.

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i have found with my car that in gear coastng shows higher milage reading on my scanguage than neutral coasting.

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"Sylvie" 2000 Honda Insight 5 Speed


http://www.gassavers.org/gaslog/sig.php?id=196

Really? That's very interesting. Do you know if fuel is being injected or not? For example, on the Camry, depending on coolant temps, when I coast (in gear) and drop below ~1200-1500rpm fuel starts being injected, and it pretty much idles down the road in gear. But if I'm coasting (in gear) above those rpm in top gear (greater than 50mph), no fuel will be injected. I'm wondering if the fuel flow for in gear idling is the same as N idling...

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I'll have to check gph readings and see.

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"Sylvie" 2000 Honda Insight 5 Speed


http://www.gassavers.org/gaslog/sig.php?id=196

My SG does the same thing, but what it doesn't know is that the injectors actually cut fuel while coasting in D (so it should read 9999).

Several vehicles benefit from Neutral idling -- the GPH arguement is quite valid. For maximum efficiency, long idling situations should be in engine-off mode (like at traditionally long lights, etc).

BUT...

The TSX, for example, has variable cam timing (i-VTEC) that cuts the cam timing dramatically at idle and uses very little fuel. It actually uses more fuel to shut-down and re-start if you're not sitting for at least 2-minutes (according to the on-board FE recorder). I don't use neutral idle anymore in the 'Teg either, as I'm worried about the longivity of the transmission going from N to D at a stop (a bit of a hard engagement). Coasting in engine-off N, starting up, and back to D with a rev-match seems to work well, tho...

RH77

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Same with my dad's Chrysler. It depends on the car whether its sensitive to being in gear or not.

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According to Ben (SVOboy) the fuel injectors on hondas turn off while coasting in gear, so the same goes for us.

Do you know if this applies to all Hondas? I generally drop into neutral for short coasts and turn the engine off for longer coasts because when I eave it in gear it slows down considerably faster and I know that when I'm stopped that going into N will save gas. I would just experiment, but I don't drive very often except when I'm on a job, so for me to go from tank to tank would be difficult, and I don't have a SuperMID.

Using liters instead of gallons on the SGII will give better resolution of the idle fuel consumption. I found that my idle fuel consumption at a stop went down about .1l/h in neutral. One gallon = 3.785l. Watch for any transitional changes that may eat up any gains over a short time out of gear.

If you do a lot of ICE-off coasting, changing the SGII engine type to "hybrid" and keeping the key in the "run" position as much as possible should give the trip mileage better accuracy.

GPH Fuel consumption in my car is about the same coasting in neutral or drive, but above 30 MPH it slows down faster in drive because of engine braking. MPH/GPH = MPG, so the faster you're going during ICE-on coasting, the better the gas mileage. ICE-on coastdowns in neutral at high speeds will give better gas mileage in my car because it remains at high speed longer.

It doesn't appear to me that you guys are differentiating well between coasting with engine on and engine off. When you are coasting with engine off NO fuel is being consumed. So how can your fuel consumption be less than that? Coasting in gear only slows your car down faster, how can that be good? If there was total fuel cut at any time with any car, the engine would die. Engine Off Coasting is a sure fire way to substantially raise your FE. It worked for me and has worked for many others.

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CO ZX2

garage/view/239

100+MPG Fill

Coasting Info

Front Fender Skirts

Turn off the fuel injectors, and the engine will die! Will it not? Does it restart itself, too? I'm confused....

All modern FI cars should have the injectors turn off (or maybe pulse depending on the post cat O2 reading) above a certain rpm with no throttle, depending on coolant temps (maybe other things too?), when the vehicle is above a certain rpm in any gear. Once the engine drops below a certain rpm, the car starts "idling" again, in or out of gear. I suppose manufacturers could tie the transmission switch into the vehicle idle, but the problem with this is if the switch goes, the car can stall at stops.

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If your speed is high enough the most auto trannys will spin the motor if you shut it off, So at higher speeds cutting fuel would not kill the engine.But once you get to a lower speed the tranny will stop turning the motor and engine will kill.

ELF. You are wrong on this one. If the fuel is shut off the engine is killed, not running under it's own power. Even though the engine is turning, it is being powered through the transmission, transmission being powered by the wheels. This scenario results in reverse FE. You are using energy you have already generated to turn over a dead engine. Not that hard to understand. Does this make any sense to you??

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CO ZX2

garage/view/239

100+MPG Fill

Coasting Info

Front Fender Skirts

Coasting in gear doesn't have to equal reverse FE. You can coast to stops or in locations where it would be advantageous to have the resistance to keep you from going 90 down the hill and dying.

Ted, the fuel is cut and the engine becomes an air pump as it is still connected to the wheels and rotated through that physical connection.

I've found that to be true in my old honda (89) but not true in my new honda (2007)

I was only trying to explain to Ted that the engine would still be turning over at speed and not completely stopped, so it wouldn't have to restart. I didn't mean to imply the FE would be better.

[QUOTE=omgwtfbyobb If you have the time, could you check the fuel flow when coasting in N compared to decelerating in gear at a kinda slow speed, like ~40mph? If the idle consumption when decelerating is greater than coasting in N, then coasting must be a win win no matter what.[/QUOTE]

I checked today, hitting neutral at 40 mph....GPH was at .07 no throttle in drive.
switching to N at 40mph.. GPH went to 0.9 for about 2 seconds and then went back to .07

Seems to be no help going to neutral for coasting , at least in my car.

But at the same time though you're losing inertia energy because of engine braking. If you drop it into neutral, you'll coast longer, or at least that's the case with the cars I've owned.

Exactly. In my case, I loose energy twice as fast with the car in gear, so since the idle rate is pretty much the same in both cases, coasting in N must always be a win-win situation.

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Your right, I wasn't thinking about engine braking just the SG readout. I did some neutral coasting today, my tranny shifts back in gear real smooth and easy even at speed so I'm going to see if this helps with overall mpg.

If your engine runs extreamly rich on start-up, then to restart your engine can use more fuel, then if you had let it sit there idleing if it would only have been idleing for a few seconds.

I have noticed that on my newer car (2002 Mazda Mpv with auto trans) when I lift the transmission disengages and the engine falls to idle. When I hit the throttle the trans reengages. The MPV is a ULEV and to keep the converters at temperature the exhaust gas has to be hot. So no fuel cut while coasting. This is my guess......

So FE is sacrificed for emissions in this case. Pllus it makes for some nasty bumps from the driveline while driving in traffic, not so good.

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B W

http://www.gassavers.org/gaslog/sig.php?id=292
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Hello -

Idling at neutral at speed X gives me roughly a 3/1 ratio of MPG/MPH :



When I am in gear at these speeds, the increased RPM decreases to roughly a 2/1 ratio. This tells me I am still injecting fuel, even when my foot is off the accelerator pedal.

CarloSW2

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Don't believe your scanguage GPH (or mpg) reading in an overrun condition.

Strange as it seems - I see fuel being injected at .3gph going down First Beach hill at 25-30mph with foot off gas in gear but I also do NOT see the engine temp rise - if I put it in neutral at the bottom of the hill to coast a little I see the same fuel burn rate and the temp increases . . . indicating that the injectors are being driven but no fuel is getting into the engine when going down the hill (engine braking). This may also skew the fuel use in the SGII at fillup showing more fuel used than actual if engine braking is used a lot for the tank of gas.

I think i got it figured why i sometimes see a high mpg reading when coasting in gear. out of gear coasting my engine idles a bit higher than when stopped and when in gear it drops and i think thats why i sometimes see higher readings.

I have started doing alot more Engine Off Coasting and it's showing on the SG, now just gotta see what it shows at the pump.

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"Sylvie" 2000 Honda Insight 5 Speed


http://www.gassavers.org/gaslog/sig.php?id=196

LxMike -

The SG is way off for me in that condition. It is always a 10/1 factor. If I am coasting with engine off at 39 MPH, the instantaneous display shows 390 MPG on the SG. Since this is an "infinity condition", aka divide by zero (something akin to X MPH / 0 RPMs), I think the SG is just pasting in a safety number to keep from going bonkers.

What is interesting is that for my car, this might mean that I am getting better MPG for "run X" than the SG is reporting. If it is averaging in "10/1" MPG for the period that I am coasting with the engine off, then it is lowering my actual MPG figures.

CarloSW2

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skewbe -

Do you really think so? I was hoping to *infer* gas consumption from SG behavior.

From reading saturnfans.com, this behavior is consistent to what other people have written. What they say is that fuel injenction does decrease, but does not get very close to zero until you almost reach the car's idle RPM. However, at the idle RPM, the fuel injection will be maintained in order to keep the engine turning over.

The following is *NOT* the post I got this info from, but it does talk about ECU/PCM behavior in Saturns :
http://www.saturnfans.com/forums/sho...0&postcount=25

That's what drives me nuts about the SG. I don't know how it is programmed. How does it actually derive fuel consumption? Since it is a jack of all trades, it must be using lowest common denominator inputs across all OBD II implementations.

I mean, why does it need to know my engine size? For real accuracy, it should only be looking at the actual amount of fuel being injected into the engine. If however, it is extrapolating the fuel consumption by monitoring other ECU/PCM input data, then the engine info makes more sense to me.

I love the SG, but it really just makes me hunger for one of the high end engine data monitors that are in the $500+ range.

CarloSW2

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