diy mpg gauge

[itjstagame]

Originally Posted by skewbe

One last note, trying to determine distance from rpm and gear ratios wouldn't work for me, I spend most of my time coasting with the engine off. I really need that vss signal if I want to know how far I've travelled (the 'M' in 'MPG').

Ah, very good point. Yeah, VSS is easier, I was only saying that if you only had a mono jack, just that you could get fairly close with one signal.

For calibration there are a set number of VSS pulses per mile, speed is just the rate of pulses, but I'm calibrating toward the constant number of pulses per mile?

Also how'd you decide how much fuel to attribute to each pulse? Do you have some formula based on the cc of each injector? Becaues obviously 50% pulsewidth isn't an exact amount of fuel, only if you know how much fuel the injector delivers at that 50% pulsewidth. And do most injectors ramp up linearly? ie. 80% pulsewidth used exactly 60% more fuel than 50% pulse width?

Lastly, I can solder and I can follow a diagram, but I'm afraid my electronic skills fail at the basics, so if I'm told I want to output a constant .6V I don't know if that means I need a resistor a transistor a whatever, etc. Can you give me an idea of what kind of diodes you use and what rating (varies based on VSS out signal I'm sure). And it looks like you hook the + audio signal to before the diode bridge but still on the negative (grounded) side of the VSS/injector? Or do you tap in to the + side and use the - only after the diode bridge, also aren't you making the whole ground for that injector pass through that bridge, is that an issue? Can I just use any common ground in the car? This seems it might work for the injector, but the VSS is a stand alone pulse (probably VAC)?

[itjstagame]

Actually I guess the only other signal that would be nice to have is TPS. Then you can compare throttle position to pulse widths and various loads.

I don't think I like MPG as an indicator, I'd like to see acceleration or maybe energy produced per gallon. I often wonder is accelerating slowly at 12MPG is better than accelerating quickly at 8MPG, etc. Finding the most efficient spot for acceleration coupled with EO P&G should help a lot. I would assume this would be maximum torque rpm, but I wonder how much of an effect throttle position has, especially with today's ecus, even at the max tq rpm, if you're cruising or WOT it's very different, typically different target AFRs and advances. Even building my own ECU I'm not sure 'theoretically' which would be better, lean is for efficiency but more power seems more efficient (unless it's less power/Gal).

Maybe the cruising/leaning is simply to try to help the fact engines aren't as efficient maintaining a steady state load versus accelerating against a load? That's why stuff like dropping out cylinders helps?

Sorry I keep posting, I'm just anxious to get playing with my vehicle and can't at the moment.

[caprice]

I'm lost here, but excited too... what do you have "do" to use this DIY MPG Monitor?

I know a little bit about programming, and my brother knows Java, so that helps.

In fact I have used "WIN ALDL" and an old computer to track the performance when I upgraded to TBI in my car.

[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.

[GasSavers_Doc]

I've got mpg.java to work but have not sure how wire anything to it yet. Trying to work out how to code Java so I can get an Oxygen sensor reading as well. Can this kind of app run off two sound cards so we have 4 channels.
Very Impressive work!!!

[mpmetro]

Here are some pics of my circuit I made. I am not sure if it Is right, but I tried. My wires arent too thin are they? (speaker wires) And I put it in a nice box. I still have to connect it to my laptop and calibrate. (going to connect it to an older computer first, just to make sure, I dont fry my good laptop)

one more question... since my car is a 91 metro 3cyl, similar to your metro skewbe (is it 3cyl ?), I was wondering if I will still have to do all the calibrations etc...

[cfg83]

mpmetro -

Originally Posted by mpmetro

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Plastic box containter. Righteous!

CarloSW2

[itjstagame]

Originally Posted by mpmetro

Here are some pics of my circuit I made. I am not sure if it Is right, but I tried. My wires arent too thin are they? (speaker wires) And I put it in a nice box. I still have to connect it to my laptop and calibrate. (going to connect it to an older computer first, just to make sure, I dont fry my good laptop)

Ok, that's what I understood from diagram posted earlier, but I still can't tell if you're tapping inline to the 'ground' from the injector or if you're bridging off or if you're tapping into the positive side.

I'm also still confused on what the diodes do (which is fine I don't really need to know ) and I'm confused why VSS signal would be hooked to a common ground, I picture it acting like the pulsing coil on my motorcycle, it's generates a small VAC current due to the magnet going toward and away from the circuit.

Also I was going to swap the 10k res for a 25k pot for calibration (I just need to be unlazy).

[skewbe]

looks right, you might want to use shielded wire to the probes and ground them near where they tap into the signal for less noise.

You might get lucky and not have to calibrate. I'm a little confused on right vs left so you may need to swap those to get it to work right.

[sonyhome]

skewbe:

I'd love to code the program to make what I think would be a great hypermiling diagnostic tool, I have quite a few ideas on how to present the data usefully. However I need lo learn Java first . I did look at the graphic libraries, and it's too bad, it seems one has to code the graphic interfaces (for like 2D graphs, gauges etc.) so there's some overhead work to make a cool tool.

I think the config file you have is pretty well thought, it does allow adjusting the tool.

itjstagame :

With this gizmo you could have what you want. It's just a matter of programming.

Caprice:

I think it boils down to this:
- Find Vss and one injector wire
- Solder wires to needles and stick them in to tap those signals.
- At the other end, follow the diagram, aka solder to a 1/4" (?) headphone plug (each wire to center connectors and the diode bridges between those wires and the outside ground connector), and the ground to the car's chassis. Note that there's a resistor there, and it's to make sure you don't just ground the signals with the diodes. When the diodes pass current, it's via the resistor, which makes the current draw very small.
- Boot your PC or whatever, and run skewbe's Java app. For that I personally made a batch file that just calls the java program, else Windows doesn't launch it (maybe one needs to register the .java extension as a runnable program?).

The program works w/o the car: just with noise on the microphone it'll do some random stuff.

mpmetro:

That's some ugly soldering LOL
make sure that glue holds tight.