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.

[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...

[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.

[cfg83]

mpmetro -

Originally Posted by mpmetro

...



...

Plastic box containter. Righteous!

CarloSW2

[mpmetro]

Originally Posted by sonyhome

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

i know... i cant solder.

[itjstagame]

Originally Posted by sonyhome

itjstagame :

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

I've already done some of the programming. Java was new to me too but not that hard to pickup. I added a way to 'guess' VSS pulses based on tire size and final gear and a way to calibrate vss pulses over a given number of miles.

I'm also trying to add the cid and crr calculations but stopped at trying to figure out how to use the actual temp, pressure and humidity to get air pressure index. Also I didn't want to release anything until I could get it installed and calibrated (and debugged!) in my truck, but I'm kind of scared to throw a resistor in line with the negative on my injector and can't find my VSS (tons of wires to my trans and transfer case and not sure what I need). For now I'm just using small tankfuls and trying to drive (I have no time to work on most these things anyway).

A graph might be nice but I think I'd rather see a more 'gauge' like interface (with a needle). The only other diagnostic I'd like to add is instantaneous HP/power and keep track of that over trips too.

For instance the same trip done at 45MPH and at 75MPH, the 75MPH will neccisarily have to have generated more energy/hp and most likely used more fuel.

I was also wondering about trying to find a pinout diagram of my ecu and pull signals there. Not the processed signals from an ODB connector, but the actual inputs to the ECU and bridging them.

[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]

sonyhome: Yes on all accounts

itjstagame:
I believe my injector has a switched ground, so I'm on the other side of that, counting on the voltage drop across the resistor to give me a signal.

My VCC is a switch, which mysteriously does go positive and negative??? Don't care. The wagon is a magnet, or a hall effect thing, I expect that might take some figuring at slow speed and/or an op amp.


anyone: You can mess around with my wav recording for defaultFile. It's a bit more relevant than mic noise. It's too big to post so PM me your email and I'll forward it,2.5 meg. Tell me if you think the rpm "whine" on it is the alternator if you listen to it.

[itjstagame]

Ok, so you're on the same leg with the resistor in the middle, sounds good to me. I still worry about changing the ground of my injector (through a resistor) affecting pulsewidth, but I guess it doesn't matter and I can always change it back if there's a problem.

Yeah, I suspect VCC to go positive and negative but I guess that's all good too. Just need to find my VSS and start splicing.