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    On-Line Gasoline MPG Calculator (Using MAF and/or MAP/IAT/RPM)

    For those that want to calculate MPG using MAF (and/or MAP/IAT/RPM) for gasoline vehicles I've put together a Webpage with a Javascript-based air/fuel flow calculator...
    ...
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    OBD-II Scan Tool Detection Schemes

    One issue with rolling your own MPG gauge and possibly "hard-wiring" it onto your vehicle's OBD-II bus is the issue of coexisting with any factory scan tools that might be plugged into your vehicle's...
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    Calculating MPG / Using a "Constant" A/F Ratio

    You should be able to make this work---I know because I have. As I've told people that have contacted me via email, the "hard part" of implementing a real-time MPG meter with embedded firmware is...
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    Using OBD-II LOAD to derive MAF

    There seems to be at least two different interpretations of the OBD-II parameter called "engine load" (i.e., LOAD, in the range of 0-100%), as reported over the OBD-II bus by modern engine computers....
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    How to "calibrate" OBD-II derived MPG when using IMAP

    "Plug-and-play" MPG calculation from OBD-II bus parameters is not out of the question for many vehicles---not just MAF-equipped ones. It all depends upon what is available on the OBD bus---from...
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    Been there...done that. As it turns out, this is...

    Been there...done that. As it turns out, this is a very "doable" project if you happen to have an OBD-II compliant vehicle with a MAF sensor---plus MAP, IAT and RPM sensors (almost 100% of OBD-II...
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    "Over-Correcting" MPG Using Long-Term Fuel Trim

    Marc is right. A modern vehicle's engine computer (ECU) constantly works to maintain a "stochimetric ideal" air-fuel ratio of about 14.7:1. The reason for this is emissions regulations, and not...
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    Let's Get the MPG Formula Right!

    For the record, the first "one-line" MPG formula above, taken from my Circuit Cellar article, is off by 100! The "4.54" should in fact be "454". The correct formula is:

    MPG = (14.7 * 6.17 * 454...
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