DIC MPG vs. Calculation By Hand

[mikennola0515]

Any idea as to why the DIC calculation would be consistently lower (by a couple MPG) than a manual calculation (dividing elapsed miles by gallons to fill the tank). By DIC calculation, I'm not referring to the "instant" fuel economy computation, but rather the one obtainable by using the "Business" odomoter, for example.

I keep track of every fill-up (always fill the tank completely) in this way.

Thanks,

Mike

[Dakster]

Is your truck completely stock? No programmer, exhaust, after market air filter, etc... etc.. All can effect the DIC computation.

THe one thing that seems to consistently work on my truck is the DIC Avg. MPG. It always seems to be within .25 mpg of my hand calc. (which means I probably are not filling up to the same point each time)

[Kennedy]

I have found the DIC calculator to be very accurate when not messed with. Most all aftermarket tuners mess with it though. I've deliberately steered clear of mods that affect this when doing my Economy tuning. I reset the gallons used and mpg each time I fill up. Sure it's all over the place at first, but it works out in the end. It's also a great tool to use to train yourself to drive smartly...

[Spoolmak]

I live in Canada and our gallon is 4.54 litres. My truck though has the software calculate MPG average as if it were a 3.79 litre gallon. If I calculate it manually, it is right on in terms of Canadian gallons used and miles travelled. That MPG figure is 20% higher than what the display tells me. Of course when I set the computer to to calculate kilometres and litres per hundred kilometers, it is right on. You'd think GM could do a software flash to help us Canadians. Even though we travel kilometres, buy fuel in litres, some of us still judge efficiency in MPG. Ayup, I do have grey hair....

[jbplock]

Any idea as to why the DIC calculation would be consistently lower (by a couple MPG) than a manual calculation (dividing elapsed miles by gallons to fill the tank). .... I keep track of every fill-up (always fill the tank completely) in this way...

Mike,

My 03 is stock with regard to ECM programming and has behaved the same as yours since it was new. I fill up and reset then trip odometer at each fill up and it's always 1-2 mpg higher than actual value (miles driven divided by gals used). I also use the business odometer for tracking oil changes and it's average mpg after 5-7 kmi is a little closer to actual but still higher. Might just be my imagination but it seems like the spread on mine has increased with age. I've often wondered if it correlates to increasing injector balance rates .. at 81kmi mine are still in spec but 1 or 2 are are near the limits.

:)

[mikennola0515]

I should have pointed this out earlier, but I have no modifications from stock (no chips, tire size changes, etc.).

Sorry for the delay in responding.