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Originally Posted by Jalberdi99
Do i reset it before filling up or after filling up? Or it doesn't matter?
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When you get in the car after filling or just before you get out before filling. It really dosen't matter. Just never reset it between fillups and compare it to a manual calculation. It will be way off then.
I have 32 years experience in flow calculating instrumentation and unless your injectors are severely clogged or worn the calculations done by the Computer will be fairly accurate. The more wear or clogging of the injectors will affect the calculations. The calculation done by the computer relies on the pulse length that the injector remains open. The more pulses the more fuel used. But I would expect it the injector problem would have to be so bad that the actual performance decrease would also be noticed.
Even though the fuel pumps where you get gas are supposed to be calibrated and certified the longer it goes between calibrations the more error it has in the amount of fuel it delivers. Another factor in manual calculations is different pumps have different cutoff points, what this can do is cause a inconsistent refueling of your vehicle. All of which affects calculations of fuel mileage.
The best way to figure mileage to reduce percentage of error is to add up the gallons over several tank refills. Then you can use the miles you drove during the same period. I usually do that when on trips, and its then when I have found the DIC to be fairly close to my manual Calculation.
I hope this helps.