# Fuel Used value



## 70AARCUDA (Nov 14, 2010)

...it's a "calculated" value, determined by the Engine Control Unit (ECU).

...basically it's a 'totalized estimate' of how much fuel the ECU has commanded the injectors to squirt into the engine.

...sum-up (roughly) how much gasoline has been used, convert that value into gallons, then divide it into the distance traveled, for an approximately accurate "Average MPG" number.

...FWIW, the displayed value seem to be _consistantly_ about *5%* LOWER than the actual, tank-fillup, value...at least for our LTZ.

...what are other people seeing?


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## SilverCruzer (Nov 30, 2010)

70AARCUDA said:


> ...sum-up (roughly) how much gasoline has been used, convert that value into gallons, then divide it into the distance traveled, for an approximately accurate "Average MPG" number.


What I have noticed is the computed calculated avg mpg is exactly this value divided into the miles on my trip odometer.
I was wondering of the three variables in the calculation, which one(s) are real? If the fuel used is real, then there is no point in trying to compare mpg using what the tank fill up says since I am suspect of the reliability of how much I pump based on top off click, no top off click, cut short click, etc. What it seems is the only real variable is the miles, then to get avg mpg, the computer does what you mention to calculate fuel flow.


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## 70AARCUDA (Nov 14, 2010)

...MILES are real, coming directly from the trip odometers (A or B). It's the GALS values that are only 'approximate', hence:

MPG(approx) = MILES(accurate) / GALS(approx)


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## SilverCruzer (Nov 30, 2010)

Yeah, I knew the miles were real.
All being said, I tend to think the gallons used calculation is more accurate than when I check the "gallons bought" at fill up because I don't really know if I am actually filling it up consistantly.


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## 70AARCUDA (Nov 14, 2010)

SilverCruzer said:


> Yeah, I knew the miles were real.
> All being said, I tend to think the gallons used calculation is more accurate than when I check the "gallons bought" at fill up because I don't really know if I am actually filling it up *consistantly*.


...that's *why* the *'ONE-CLICK'* method is recommended by *ecomodder* nuts (like me):

1) Fillup at the _same_ gas station at about the same time of day.
2) Use the _same_ gas pump, with car level as possible.
3) Insert/position the gas nozzle aligned _vertically_, not leaning to either side.
4) Use the _slowest_ 'automatic' filling setting on handle, do not use hand control.
5) Let the pump run until it _automatically_ "clicks" OFF--you're done.
6) Always use this SAME process.

...the above process won't be 100% perfect, but it _will_ minimize the small tank-to-tank variances between subsequent refills.


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