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 Post subject: DIY MPG Gauge
PostPosted: Sun Jul 22, 2007 2:33 pm 
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FYI, the best thing you can do for improving MPG is to have timely feedback. If you have a laptop or tablet in your car with a line-in, you can make your own mpg monitor for a couple bucks:
http://www.gassavers.org/showthread.php?p=64732

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PostPosted: Sun Jul 22, 2007 11:04 pm 
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is this for newer cars only, or will it work on my 91 metro as well ?


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PostPosted: Mon Jul 23, 2007 8:10 am 
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It should work on any electronic fuel injection car. It uses the computers sound card to watch what the injectors are doing and to watch the vehicle speed sensor.

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PostPosted: Mon Jul 23, 2007 10:22 pm 
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I tried reading you tutorial again, but i'm still a novice at electronics. Where did you get the VSS and Injector signal from ?
Was it from the ECU or the ALDL connector under the dash?

my car is a 91 metro.


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PostPosted: Mon Jul 23, 2007 11:20 pm 
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on my 98 3 cylinder:

There is a yellow wire going to the injector resistor (drivers side firewall heatsink affair), I attached one probe to that for the injector signal.

Under the glovebox I found a yellow wire with a green stripe going into the pcm, tapping into that provided the vss signal.

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PostPosted: Tue Jul 24, 2007 8:48 am 
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I will have to look up schematics and try to find those wires on my 91

thanks :D


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PostPosted: Tue Jul 24, 2007 12:59 pm 
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I still have too many question on how to do this. I really want to but I guess I am not that good with electronics. I dont know what kind of resistors and diode to use in the circuit from your schematic (dont want to fry my audio input)

And I have found where to get the VSS and injector signal from, but I dont understand the software on the computer. I understand its a java code, but will I have to compile it to make an exe and will this run under windows? so basically does the software just translate the incoming audio as speed, distance and mpg etc...

I guess I will just have to wait, until someone makes a much detailed tutorial on how to do this for us novice users.


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PostPosted: Tue Jul 24, 2007 3:52 pm 
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Me too.
john :D


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PostPosted: Tue Jul 24, 2007 4:21 pm 
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could you please upload the compiled java program that you wrote, I would like to download it and try it out.

thanks :worship: :worship::worship::worship:


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PostPosted: Tue Jul 24, 2007 10:07 pm 
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Here is the compiled java jar:
http://www.gassavers.org/showthread.php ... #post65266

I used 10k resistors and signal diodes from radio shack, couple bucks worth of stuff.

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PostPosted: Fri Jul 27, 2007 1:47 am 
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The cheapest way I know of is a vacuum guage. Running it with the highest possible vacuum reading will give the best possible mileage, not changing anything other than throttle position.

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 Post subject:
PostPosted: Fri Jul 27, 2007 7:18 am 
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Actually, if you have a laptop or tablet (or in car computer), this is now the cheapest way as it is a couple bucks worth of hardware :)

The vacuum gauge cannot be calibrated to tell you how many mpg you are getting and will not give you average readings (very important for P&G, the most fuel efficient driving style ), but for granny style driving it can be effective.

http://www.gassavers.org/showthread.php ... ght=vacuum

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 Post subject:
PostPosted: Sat Jul 28, 2007 9:00 am 
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hmm. If I could just see a picture of this, I would start on one for my self, ans possibly make a simple tutorial to help the novice people.


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 Post subject:
PostPosted: Sat Jul 28, 2007 9:33 am 
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I may do a permanent install and better documentation, but I have a lot of "how do I permanently install a computer and display" stuff to sort out first. My ramline 510 is acting up, and lots of other nitty gritty details, so it will be a while.

A picture wont tell you much, the schematic is much more useful.

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 Post subject: DIY MPG GUAGE TUTORIAL
PostPosted: Mon Aug 27, 2007 9:16 pm 
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I would like to make a tutorial on how to make this DIY mpg guage, for the people who needed a little help. All credit for all of this goes to skewbe, who originally though of this and made this possible. I am sorry if the tutorial is a little messy, because its hard to explain this type of stuff.

The way this MPG guage, works is that it collects the signals from the Injector Resistor, and the Speed Sensor (VSS) and sends them as Audio Signals to the computer, and then the program that skewbe has written, converts these audio signals into MPG, distance, speed and other various readings. It gives Real-Time MPG.

Things You will need:
- Laptop or computer (in car) with Audio in, or MIC input
- Bunch of wires
- Stereo Connector (can get off old headphones)
- (2) 10k resistors
- (4) Diodes
- MPG Software (download Here: http://rapidshare.com/files/51737905/MPG.zip.html )

First of all, you need to assemble this simple circuit.Here is the schematic you need to follow: (make sure the circuit and soldering is good, and none of the wires are touching each other, because we dont want a short to mess things up!)
Image
Here is a picture of the circuit assembled:
Image

Here is a picture of the stereo connector I used. Just connect the wires coming from the stereo connector, to the wires coming out of the circuit as they are labeled:
Image


Now locate the Injector Resistor and VSS signal wire in your car.
See in the picture, the injector resistor is a silver heatsink looking thing, and the VSS wire is (green and yellow) and will be coming out a connector on you ECU.
Image

Image

First connect a long wire to the yellow wire that is coming out of the Injector Resistor. You dont have to cut the original wire, just place it in the yellow connector and close it.

Image

Image


Then run the wire that you connected to the yellow injector resistor wire to inside the car. (I made it go through the hole that the A/C uses to drop out water)

Next Remove you Fuse box under your dash by removing two screws, just to get it out of the way so you can see your ECU. There will probably be two plugs going into the ecu.
Look at this thread for more info on the pin out of your ECU: http://www.teamswift.net/viewtopic.php?t=28842

Look for a Yellow and Green wire. That will be the Vehicle Speed Sensor wire (VSS). Connect another long wire to the VSS wire.

Next find a ground spot. I just used a screw that was connected to the metal body of the car. Connect a long wire here also.
Image

Should have something like this now:
Image

Now comes the part where you connect the 3 wires coming from your car, to the circuit that you made.
- Connect the injector wire coming from the Injector Resistor to the Injector wire on the circuit, -
Connect the VSS wire coming from the ECU to the VSS wire on you circuit.
- Connect the ground coming from the body of the car to the ground wire of the circuit.

You should have something like this right now (dont really need the box :P )
Image

Next connect the stereo connector to the input of your laptop. Make sure that under audio Recording control settings, your laptop is set to INPUT from microphone, or from Line-IN.
Image
Image

If you have not done so, download the software from the link above, extract the 2 files to some folder. Make sure you have the latest version of JAVA, (or download it at JAVA.com) Test run the MPG Monitor.exe file, and a dos window along with a grey window should open:
Image

Now start the car, connect the stereo jack to your laptop, and start the program. The readings may jump a little at the beginning. But anyway, go for a test drive in a small quite street, with no traffic just to check things. Compare the speed the monitor gives and speed on speedometer. And the mpg reading should be somewhat accurate.

NOTE: If the speed is jumping really high when you start the car, and not moving at all, it is possible that you got the injector and VSS wire mixed up. So simply switch them over, and try again.

I wanted to make the text bigger in the program, but dont know the java to do it, so to make it appear bigger, I just reduce the screen resolution, so its easier to read while driving.

WARNING!!!: I would not suggest you actually use this on a real trip through traffic unless you have the system mounted in a such a way that it does not distract you from traffic and driving. I am not responsible for anything happending to you. Even I have not used this system in real traffic yet, but will do when I have done a permanent install with a small car PC lcd mounted. Also I advise you to test it with an older laptop, because you dont want to mess up the audio ports. It shouldnt harm your laptop if you correctly made the circuit, and all wiring. I have been using it on my $500 dollar laptop, and it works great.

Picture of laptop connected:
Image

Once again all credit goes to Skewbe, who thought of this MPG guage. It is his invention. I simply made a tutorial following his directions.


Last edited by mpmetro on Tue Aug 28, 2007 9:57 pm, edited 1 time in total.

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 Post subject:
PostPosted: Tue Aug 28, 2007 1:16 am 
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Location: Milwaukee, Wisconsin
Nice tutorial! Always like when good pics accompany text. :D

Now I have to set about finding a cheap laptop.

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 Post subject:
PostPosted: Tue Aug 28, 2007 4:37 am 
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Sweet!! Thank you mpmetro!

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 Post subject:
PostPosted: Sat Oct 27, 2007 10:51 pm 
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i would say a vacuum gauge is still cheaper than a laptop.


i use a vacuum guage and a wideband.

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 Post subject:
PostPosted: Sat Nov 03, 2007 8:39 am 
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vacuum gauge is cheaper yes. Wideband? not always, and not cheaper than a pre-built mpg gauge (i.e. scangauge, supermid). But if you were a total geek and installed a computer in your car for mp3 and navigation maps and cheap webcam rearview and whatever else, then something like this makes a lot more sense if you are mpg conscious.

This (or a scangauge or a supermid) has a couple huge advantages over a vacuum gauge or o2 meter (been there), namely it has average readings as well as intantaneous , and they are calibrated to mpg.

With just instantaneous readings (even if it were actual mpg) you may never learn the optimal strategy for, say, approaching a hill, or for navigating other obstructions in the flow of traffic. If you decide to try the most effective fuel saving technique, pulse and glide, an average reading of some sort is a must in my book. I manage around 70mpg CITY with a scangauge and a kill switch and a lot of practice.

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 Post subject:
PostPosted: Fri Feb 01, 2008 7:35 pm 
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Location: Abbotsford, BC
skewbe wrote:
vacuum gauge is cheaper yes. Wideband? not always, and not cheaper than a pre-built mpg gauge (i.e. scangauge, supermid). But if you were a total geek and installed a computer in your car for mp3 and navigation maps and cheap webcam rearview and whatever else, then something like this makes a lot more sense if you are mpg conscious.

This (or a scangauge or a supermid) has a couple huge advantages over a vacuum gauge or o2 meter (been there), namely it has average readings as well as intantaneous , and they are calibrated to mpg.

With just instantaneous readings (even if it were actual mpg) you may never learn the optimal strategy for, say, approaching a hill, or for navigating other obstructions in the flow of traffic. If you decide to try the most effective fuel saving technique, pulse and glide, an average reading of some sort is a must in my book. I manage around 70mpg CITY with a scangauge and a kill switch and a lot of practice.


How did you install your kill switch ?

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 Post subject:
PostPosted: Thu Mar 20, 2008 6:22 pm 
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this seems simple enough. to put this in easy terms-this just compares how many times your injector is pulsing compared to how fast you are going, right?

MPMETRO-"?"-how did this work on your 91 metro? I have a 91 and i thought the only speed sensing on it is the cable. The 91 doesn't have an electronic speed sensor on it......?


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 Post subject: Re:
PostPosted: Sat Mar 22, 2008 2:46 am 
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disrespected3cyl wrote:
The 91 doesn't have an electronic speed sensor on it......?

It should have one in the speedometer. It's there to tell the ECU how fast you're going.

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 Post subject: Re: DIY MPG Gauge
PostPosted: Sat Mar 22, 2008 6:42 pm 
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oh, then please forgive me. I thought it was just a cable that went right from the trans to the instrument panel.


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 Post subject: Re: DIY MPG Gauge
PostPosted: Sat Mar 22, 2008 8:37 pm 
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it worked fine on my 91. I used the speed sensor signal from the ECU... But I ended up taking it out of my car, because I dont want to lug around a laptop... Once I get an integrated PC and screen in the car, I will install this again.

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 Post subject: Re: DIY MPG Gauge
PostPosted: Sun Jun 29, 2008 10:01 pm 
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How old of laptop will still work for this? My dad has a old one laying at his house in closet. I am guessing it has to be newer than his to run java.
Mpmetro how accurate was it?

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