mpg readout margin of error - DodgeForum.com


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mpg readout margin of error

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Old 06-16-2013, 03:51 PM
Deadsquiggles
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Default mpg readout margin of error

Does anybody know the average margin of error on the mpg readout in these trucks? Mine tells me I'm averaging 14_15mpg but if i hand calc it, I'm only getting 10mpg. I didn't think the computer would be that off.
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Old 06-16-2013, 09:09 PM
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The computer can very well be that far off. The computer has no way to determine how much fuel you are using exactly, it bases the MPG reading it gives you simply off the amount of air that it is sucking in. This method is a guess at the best of times.
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Old 06-16-2013, 09:12 PM
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That's kind of dumb, to say the least.
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Old 06-16-2013, 10:30 PM
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Just made a 300 mile trip. Readout said 20.5, hand calc showed 19.3
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Old 06-16-2013, 11:02 PM
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Mine was within a couple MPG's. If your only getting 10 mpg via hand calc, something is wrong. I've seen bad numbers before, but never that low, unless your towing a 10000 pound boat uphill with the AC on....
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Old 06-17-2013, 10:29 AM
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I just did a big trip and mine read the opposite. The computer read 19.2 though hand calc'd I cleared 20.6 or 17.794 Gallons of Fuel for a 368 mile trip on mixed highway conditions.

My computer used to be closer to exact, until I changed to a Hipotek TB and the Superchip tuning. I think the most noticeable variations came shortly after the tuner.

I agree though, if you are running 10 MPG, either you are calc'ing something wrong like not starting out on a completely full tank, or you are constantly full throttle on and off, but still that shouldn't give you 10 mpg. My worst was like 12 or 13 mpg, but I had 2500-3000lbs on a trailer and I wasnt gentle...
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Old 06-17-2013, 05:19 PM
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I went from a full tank to a 1/8 of a tank and I got a 186 miles out of that. I try to be easy coming off stop lights. The only time I really get into it is when I'm on the highway and I pass somebody. Other than that, whether it's city driving or highway driving, I'm fairly tame with the throttle. I just swapped out my air filter and that helped a little bit so I still think my crappy mileage has an underlying cause. Problem is money don't grow on trees so even if I knew what it was, I still might not be able to fix it.
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Old 06-17-2013, 06:48 PM
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Quote:
Originally Posted by Deadsquiggles View Post
I went from a full tank to a 1/8 of a tank and I got a 186 miles out of that. I try to be easy coming off stop lights. The only time I really get into it is when I'm on the highway and I pass somebody. Other than that, whether it's city driving or highway driving, I'm fairly tame with the throttle. I just swapped out my air filter and that helped a little bit so I still think my crappy mileage has an underlying cause. Problem is money don't grow on trees so even if I knew what it was, I still might not be able to fix it.
Calculating to a mark on the gauge isn't very accurate - you need to calculate from one fill-to-the-top, to the next fill-to-the-top. The gauge itself isn't very accurate and then the fuel level sender signal isn't completely linear, which has to do with the float and it's positioning in the tank.

The algorithm used to calculate fuel flow in the PCM can be off by a fair margin since there's no "flow volume sensor" so it needs to do a best guess on how much fuel is used per squirt plus the other factors that it can sense to come up with it's guesstimate.
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Old 06-17-2013, 07:27 PM
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Even if it's not that accurate, I'm still not getting the mileage i should.
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