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Discussion Starter · #1 ·
Does anyone know how many miles of history is retained in memory (I assume it is not infinite) and what is the formula used to calculate the MPG? I assume that there is some integration of MPG over time with possibly some weighting for recent history.
 

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Does anyone know how many miles of history is retained in memory (I assume it is not infinite) and what is the formula used to calculate the MPG? I assume that there is some integration of MPG over time with possibly some weighting for recent history.
Hit reset and it starts all over....:)
 

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Does anyone know how many miles of history is retained in memory (I assume it is not infinite) and what is the formula used to calculate the MPG? I assume that there is some integration of MPG over time with possibly some weighting for recent history.
I don't think it keeps a history. Just a constantly changing average calculated on miles travelled and fuel consumption since the last DIC reset.
 

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Discussion Starter · #4 ·
I don't think it keeps a history. Just a constantly changing average calculated on miles travelled and fuel consumption since the last DIC reset.
Based on what happens when you do hit reset, there must be some history. As soon as you hit reset, the Economy changes with every little change in throttle pressure/RPM. After a while, it gets much less sensitive to the impact of throttle wide open events, so :confused: :confused: :confused:
 

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Based on what happens when you do hit reset, there must be some history. As soon as you hit reset, the Economy changes with every little change in throttle pressure/RPM. After a while, it gets much less sensitive to the impact of throttle wide open events, so :confused: :confused: :confused:
When you hit reset while driving at expressway speeds, for instance, your MPG will immediately start out at like 35 MPG because that's what the instantaneous calculation is based on a snapshot of the engine performing with very little effort and calculated with very small (large margin of error) numbers. You'll notice, however, that it quickly falls (actually, gets more accurate) as the numerator (miles travelled) and the denominator (gallons consumed) in the equation fuel economy=miles/gallons become larger and thus more reliable.
 

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Based on what happens when you do hit reset, there must be some history. As soon as you hit reset, the Economy changes with every little change in throttle pressure/RPM. After a while, it gets much less sensitive to the impact of throttle wide open events, so :confused: :confused: :confused:
Yes and the history is what is held in memory until the next time you hit reset. Now, how many digits of memory are held is an interesting question. I seem to remember that the most often used figure is 10. I would imagine based on my observation that the DIC calculates to .00. So the ten digits could be 12,345,678.90 so it could be as high as 100 million miles. However, since it displays a decimal - I bet it goes to 5 digits so the number could also be as low as 12,345.67890 which would make 100 thousand miles of history. That makes sense.
This however is just my opinion.:D
 

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Discussion Starter · #7 ·
When you hit reset while driving at expressway speeds, for instance, your MPG will immediately start out at like 35 MPG because that's what the instantaneous calculation is based on a snapshot of the engine performing with very little effort and calculated with very small (large margin of error) numbers. You'll notice, however, that it quickly falls (actually, gets more accurate) as the numerator (miles travelled) and the denominator (gallons consumed) in the equation fuel economy=miles/gallons become larger and thus more reliable.
Reliable to a point. If you are in the low end of total miles on your car and the MPG is still improving with 'extended break in', then the history masks the change in performance.
Also, I tracked the MPG manually on my previous Saturn and I could spot trouble comming with a drop in gas economy that I could not relate to other outside factors - such as hot temp and use of air conditioning.
 
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