diy mpg gauge

[skewbe]

There's a couple ways to approach it, but referring to:
http://www.gassavers.org/showthread.php?p=64732

Assuming you can solder/record and view wav files/and understand what the program is doing given the wave forms and thresholds, and how to tweak it to make it work with your car after analyzing the signals:
1. you have to locate a good injector signal and a good vss signal. On my metro it was the yellow injector wire going into the resistor and the yellow and green wire going into the ecu.
2. hook them up to your line-in jack
3. run the program once then exit, locate the mpg.properties file it creates.
4. prepare to record line in in PCM at 44100hz 8 bits 2 channels into wav file
5. drive at a known speed (and rpm), make a guess at what mpg you should be getting, and start recording.
6. park it and save recording.
7. analyze the wave forms, if they look like mine you are done.
7a. If the are on the wrong channel, then you can fix it in the wiring or swap the processing of even and odd bytes in the processChunk method.
7b. If they are the wrong direction, then you will have to change the sign on the threshold in the mpg.properties file and the associated comparisons in processChunk for that channel.
7c. If the signals don't cross the default threshold, or noise is crossing the threshold then adjust the threshold (-128 to 127) in the mpg.properties file and/or fix your signal.

Ok, so if you made it through all that, lets "calibrate" it on the bench using your recording:
1. change defaultFile in mpg.properties to point to your recording.
2. run the program, note the speed and mpg
3. exit the program, adjust fuelfudge and vssfudge in mpg.properties a proportional amount (they are used in the divisor), and save.
4. rerun, note speed and mpg, and go to 3 if more adjusting is necessary, otherwise declare victory
5. set defaultFile back to blank and hook the computer back up to your car, enjoy.

Note, I'm considering a more user friendly version of the software, but not a priority for me at the moment. I was going to put this in my metro but the scangauge quit working in the saturn (so it is in the metro) and the saturns driver hasn't warmed up to the idea of having a computer in the car yet.

If a few of you are serious about this and understand what is going on with this cheezy bit of signal processing, PM me and I'll do what I can to help you sort it out.