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Old 01-12-2007, 08:06 PM   #21
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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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I think if i could get that type of FE i would have no problem driving a dildo shaped car.
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Old 01-12-2007, 09:21 PM   #22
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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.
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.
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Old 01-12-2007, 10:31 PM   #23
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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.
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.
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Old 02-02-2007, 09:48 AM   #24
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fuel cut

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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Old 02-02-2007, 02:00 PM   #25
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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.

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Old 02-02-2007, 02:50 PM   #26
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Hello -

...
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
Don't believe your scanguage GPH (or mpg) reading in an overrun condition.
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Old 02-02-2007, 02:53 PM   #27
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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.
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Old 02-02-2007, 04:27 PM   #28
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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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Old 02-02-2007, 05:24 PM   #29
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LxMike -

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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.
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.

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Old 02-02-2007, 05:59 PM   #30
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skewbe -

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

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