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Old 08-18-2011, 09:51 PM   #1 (permalink)
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Factory Avg Mpg Gauge isn't even close!

I have a 09 Honda Fit which has aN avg and instant fuel mileage display built in. Its usually off by 6-7 mpg. It says I'm getting an average mpg of 40, but really I'm only getting 33mpg. I'm building a car called the Gogebic XP and I want to build in a mpg tracking system. Can you guys give me a brief description of the different technologies or techniques to monitor mpg and which after market devices are best. For example, do systems measure fuel injection pulses per mile traveled or is it just a program based on the O2 sensor. Thanks,

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Old 08-19-2011, 05:39 PM   #2 (permalink)
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Originally Posted by GoGogebic View Post
Its usually off by 6-7 mpg.
That happens frequently.
My average is also off by that amount.
I've found the displayed average is further off when using hypermiling techniques.

I'm building a car called the Gogebic XP and I want to build in a mpg tracking system.
If you plan on using a commercial OBD2 compliant engine, you could get it with all the engine attributes, including the OBD2 stuff, then you can tap into that.

If you don't get an OBD or OBD2 compliant engine, I wouldn't bother and spend the time in getting it on the road rather than logging the fuel use.
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Old 08-19-2011, 05:58 PM   #3 (permalink)
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My 08 Sentra as built in MPG average only. It seems to use the same logic as my scangauge 2 that uses the OBD2 output because when I use the Scangauge to get real time MPG, the average gived by the car and the gauge come out identical once te car average stableizes (it's a bit eratic for the first few miles).

Best 15-mile commute city/highway mix: 37.7 mpg
Best tank so far: 31 mpg
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Old 08-21-2011, 10:23 AM   #4 (permalink)
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There's a TSB out for the 09 Fit's MPG gauge. There's also an engine-related recall on the 09 Fit. Take the Fit to a Honda dealer, and have them do the MPG gauge TSB while they're doing the recall work. Our 09 Fit's MPG gauge was off by that much before the TSB-indicated reflash was done. It's been within 1-1.5 MPG of hand-calculated MPG ever since we had the reflash done 20k miles ago.
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Old 09-04-2011, 04:31 PM   #5 (permalink)
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My 07 RAM's overhead is always off. It does best if I have a low mileage tank or low mileage travel for the first portion of the tank. Otherwise, it gives inflated mpg. I just watch it for giggles. My MPGuino is much better. MPGuino doesn't need OBD. It connects to the VSS and a fuel injector. Might be worth looking at.
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Old 09-05-2011, 03:09 PM   #6 (permalink)
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What you need is an MPGuino. Please see this subforum here on EcoModder.
Cost was about $50 when I got mine not quite two years ago. It's very accurate, reads fuel injector pulses and gets distance from the car's speed sensor.
OpenGauge / MPGuino FE computer - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com

MPGuino should work on any gasoline powered car with electronic fuel injection and an electronic VSS. I think it will also work on diesels as long as they have the same. Diesels with mechanical injection won't work unless you can somehow generate the electronic signal, I believe.
Coast long and prosper.
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Old 09-14-2011, 11:07 AM   #7 (permalink)
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For newer cars I think an OBD based solution would be better - a lot more info may be obtained than just the MPG.
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Old 09-14-2011, 11:39 AM   #8 (permalink)
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Originally Posted by 2009Prius View Post
For newer cars I think an OBD based solution would be better - a lot more info may be obtained than just the MPG.
...and, it does not require any "splicing" into any chassis wiring! Ultimate, "plug-n-play."

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