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Old 05-19-2015, 12:05 AM   #21
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My first tank chasing the Scangauge live MPG figure gave me a decent increase (69.5 mpg compared to 55 and 60 on previous fills, same route) - but at the cost of speed!
My car has a live bar topping at 60 mpg, but now I can focus on rolling along at 90-120 mpg on some sections of my route. These figures are just guesstimates, as they are provided by my Hyundais computer, and it is always wrong - but give me a useful sense of bad, good and better styles of driving, gears and speed. My car told me to expect 74.8 mpg when that 69.5 was the true figure.
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Old 05-19-2015, 05:58 AM   #22
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The ScangaugeE has a graph that, I think, is a metric of how efficiently you are driving. The Ford hybrids have the leaves for the same, and other new cars have something for the same purpose.

Instant MPG is almost useless on its own. The Scangauges, and others, have other data streams to use in conjunction with it. I default to Throttle Position Sensor, but there is also Engine Load and Manifold(or Boost) Pressure to use in conjunction with the instant MPG to see what you are doing, if anything, effects the car's efficiency,
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Old 05-20-2015, 01:35 AM   #23
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Any feedback is useful, instant MPG is proabbaly one of the most useful if used correctly.

This is from another well respected Hypermiling SIte:

Vehicle fuel economy feedback is possibly the most important fuel saving item one can add to their car or truck if it not already equipped. Most CleanMPG’ers see an approximate 15% increase once an add-on ScanGauge for 1996 and newer vehicles is installed. Some of the more advanced highway techniques including SHM for Toyota Hybrids and SAHM for many Honda’s make this device almost a necessity.

How else can you understand how you got the average MPG over a 10 mile journey, if you don't which parts of that journey you got high MPG and which parts you got low MPG?

How do you know when your car has shut off the fuel, if it does that, when using engine braking coing up to lights? For example, on our Skoda I know that until the engine is warm I shouldn't use engine braking as it uses more fuel than in Neutral, I can only know this from the instant MPG guage in the car.

The more information you have, the better you can make decisions on how best to drive in different circumstances to get the best MPG.

In my Skoda I would use the instant figure all the time, occasionally checking the trip average. The idea being that I try and keep the instant below the average, which will in turn bring the average down as well.

Hope this helps.

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Old 05-20-2015, 02:18 AM   #24
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But how accurate are the instant MPG readings? I find the slightest adjustment to throttle can result in the figure dropping to stupidly impossibly low figures. In neutral going down hill it reads 99.9 MPG, in gear coasting down hill it reads 0.00 MPG.
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Old 05-20-2015, 05:38 AM   #25
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But how accurate are the instant MPG readings? I find the slightest adjustment to throttle can result in the figure dropping to stupidly impossibly low figures. In neutral going down hill it reads 99.9 MPG, in gear coasting down hill it reads 0.00 MPG.
That is quite true. My wife's Chrysler Town & Country minivan has an instant fuel economy bar, and it's quite comical to see it rise and fall as a result of every different throttle position! But, as long as you don't take the information as gospel, it can still be helpful to a certain extent.

Also, I found out that I can indeed reset my MPG readout. There's only one knob to control all of the trip computers functions on my car, and you use it to cycle through the functions (trip A & B, DTE, avg. mpg, and vehicle system information) as well as to reset. I had wrongly assumed that the reset function only worked in the trip odometer mode. So, I reset it after today's fuel up and we'll see what happens over the next week.
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Old 05-20-2015, 05:51 AM   #26
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Originally Posted by Draigflag View Post
But how accurate are the instant MPG readings? I find the slightest adjustment to throttle can result in the figure dropping to stupidly impossibly low figures. In neutral going down hill it reads 99.9 MPG, in gear coasting down hill it reads 0.00 MPG.
That's because your car is using DFCO(decelerating fuel cut off).
While in gear, the ECU shuts off fuel to the cylinders while coasting. While in neutral, some fuel gets burned to keep the engine spinning.

Just because the car DFCOs while in gear doesn't necessarily mean more fuel will be saved from coasting in gear on a trip. While in gear there will be engine braking slowing the car. Great for reducing brake wear when you need to slow down or simply the speed in check. Not so great if you end up burning more fuel than saved in order to reaccelerate after the coast.

That said, instant MPG can fluctuate rapidly and wildly at times. I don't look to it to see what my fuel consumption actually is, but to see if it gone up, down, or stayed steady. That can tell me if a change I've made or in the trip conditions is good or bad, or if I simply lost focus and let my foot get a little heavier on the pedal.
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Old 05-20-2015, 07:27 AM   #27
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Mine is optimistic too! Several times during a recent 5000+ mile trip, my MMI indicated 40.2, and 40.8 mpg, but real world miles/gal math showed a high of 38 and change. Was really primed to break that 40 mpg barrier, but no joy.
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Old 05-20-2015, 09:45 AM   #28
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2 to 3 MPG is perfectly normal, that seems to be the optimistic average of most on board computers.
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