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I asked Nissan to comment on why the fuel mileage when calculated manually is always lower than the electronic method. Much to my surprise they said the computer is much more accurate than manual caculation because when calulating manually we can always be sure the accuracy of the gas pump and the amount of fuel we are actually putting in. Regardless of the amount fuel in the car if you reset the miles and average speed the computer is accurately determining your MPG. This is what they say.
 

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This is what I have said in more than one fuel mileage thread. Unless your are refueling with measured cans, there's no way to know, accurately, how much you are putting in.

Being friends with a former Indy car team owner, I've known their fuel computers can be accurate down to the lap. If they see they aren't going to make the finish, they will electronically reduce engine power and thus raise mpg to make it.
 

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fotomoto said:
Unless your are refueling with measured cans, there's no way to know, accurately, how much you are putting in.
But what about the gas pumps being regulated? They are calibrated constantly & certified. If they are off, the owner gets severely fined.

Also, what about people who state that gasoline becomes less dense with heat? A gallon bought in the hot sun is not as good as one bought in the cold night. So there is no truth to this? The Nissan computer cannot adjust for fuel density in it's calculations.
 

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none said:
But what about the gas pumps being regulated? They are calibrated constantly & certified. If they are off, the owner gets severely fined.
600 inspectors for the whole country:

http://www.cbsnews.com/stories/2008/08/21/cbsnews_investigates/main4371783.shtml


Back to the manual calculations: when and how the pumps shut off in auto mode, if the person filling continues to add gas after that, how does one fill to the exact same tank level every time, etc., are more variables that make personal calculations questionable. Is this method ball park accurate? Sure.
 

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Nissan believes they have the most accurate figure.
The gas station believes they have the most accurate pump.
The owner believes they know the real truth.

LOL
 

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I agree with you there, I drive it and don't worry about numbers.

If I drive like an idiot (Most of the time) I get around 24mpg.

If I drive sensible with no Jack Rabbit starts, and stay at or a little above the speed limit, i get 38mpg.

At $2.23 a gallon, it doesn't take much $$$ to fill the little 13.25 gallon tank and keep on rollin'
 

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Regardless of how I check my mileage (I track miles since my last fill up, mostly fill at the same station at about the same time of day and don't top it off), it pretty much matches what my computer says, within 2 miles at most.

I never do worse than 28 mpg (except in summer when I'm running the a/c constantly, I haven't checked that yet). I haven't had the chance to check it on real high way driving, though. I typically get 30 mpg.
 

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I wondered what people thought about this.. here's my .02,

Being a 13yr ase certified master tech and speed shop owner turned scca WC GT tech, I know a fair amount about what goes into calculating fuel mileage and what parameters of the fuel maps meter fuel when. The cube is very accurate from my view point on its mileage. However, there are spots in the "instant" calculations that I find holes in. The biggest is cruising idle compared to cruising full decel. A vehicle when at speed with zero throttle input actually will stop injecting fuel into the cylinders. A vehicle at speed when at idle will be injecting fuel, significantly. The cube doesn't account for this based on its instant reading. The computers basic fuel mapping is based mostly on air flow in cubic feet per min over inHg of vacuum, plotted over rpm. My guess is the cube only uses throttle position over vacuum. Other cars calculate it differently and could possibly be more accurate. Whether it REALLY matters or not, I couldnt tell you. If nissan engineers say that its more accurate than manual calculation, then so be it. My interpretation probably isnt significant enough.

On the fill up note, the only way to accurately gauge the fuel mileage is to use the same pump, at the same station and fill the car till it vapor locks and kicks the pump off. The design of the fuel filler tube and check valve will cause the pump to stop at almost the exact same time, every time. So, fill up, reset mileage, drive your distance, return and fill up, subtract fuel used divided over miles driven and boom, you got it.
 
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