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Old 10-05-2014, 02:12 AM   #1
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MPGuino

Hi guys! Sorry I haven't been on in a while. Today I did something neat to my runner that I would like to share with you!

A few weeks ago a friend of mine told me about an arduino based miles per gallon analyzer called the MPGuino. I looked it up and found a person in Estonia who currently makes kits- apparently compatible with tons of vehicles! He even adds his own enhancements that make it even better

The kit is cheap for what it includes and offers, a single kit will only set you back $61.

A few of the many features are:
-instant miles per gallon
-average miles per gallon
-speed
-rpm
-distance to empty (NEAT)
-trip cost (SUPER NEAT)
-battery voltage
-estimated horsepower
-gph
-the list goes on
-soon he is going to add coolant temp

It's an open source thing, and easy to customize if you know how to program. I do know how to program, but the thing already seems perfect. I just took it for a test drive and surprisingly the speed calibration is dead on! I think the fuel consumption calibration will have to be tweaked though, it is showing that I am only getting about 11mpg

The system hooks up very simply, to your injectors and to your speed sensor. Installation of the electronics was stupid simple. Mounting it nicely is what took some time.

To install the electronics, I tapped into the No. 10 injector wire heading to the ECU from the injectors (I am pretty sure No. 20 will work as well). I also tapped into the SPD wire heading to the ECU. The only other connections are constant battery positive and ground. Getting into the engine bay is not necessary at all, this can all be done by removing the passenger side kick panel and tapping directly into the wire harness going to the ECU.

I'll keep you updated with my calibration settings in case anyone else decides they want to try this out

Here are some pics







This is the mod that keeps on giving! Seeing a readout of how much money it costs each time I floor it really does make my foot feel lighter!

Hope you enjoy!

Last edited by jennygirl; 10-05-2014 at 02:16 AM.
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Old 10-05-2014, 02:24 AM   #2
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That would be nice to have and I like how you mounted it in one of the unused slots. Also would be in great position for visibility. Great job!!!
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Old 10-05-2014, 02:46 AM   #3
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Thank you!

I do plan on turning my car into a spaceship, so I guess I am one step closer now

Glad you like the mod! I haven't even begun to realize how much money this will save me in gas. I think the days of driving like a maniac are over...
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Old 10-05-2014, 06:43 AM   #4
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Red face

I think this is beyond quite a few to install you forget how good you are.

Still trying to hook up the DVD player that I had for 10 years now.
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Old 10-05-2014, 11:49 AM   #5
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Do you think the unit undergoes a "learning curve"? To me the most valuable revelation would be ongoing MPG, and I am suspicious of the unit being way off on what seems like a critical feature. If I have to tell it what to read, rather then it telling me what the MPG is, the whole point of it seems kind of questionable.
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Old 10-05-2014, 12:09 PM   #6
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Do you think the unit undergoes a "learning curve"? ...
You have to calibrate it. http://ecomodder.com/wiki/index.php/Mpguino_calibration How is some fancy electronics imported from Estonia going to know how much fuel your fancy injectors inject per microsecond? You have to tell it. Which might be what you were thinking of with "learning curve."

The good news is that JennyGirl is going to get hers calibrated right on the money, and she'll share her information with the rest of us. (Well, I hope she will.) She can even post her calibration numbers here: http://ecomodder.com/wiki/index.php/MPGuino

According to the seller's website (remember: the seller is some guy working in his garage. Think David Hewlett), the unit can also display "distance to empty." To know that, it has to know the size of the fuel tank, but the calibration instructions don't discuss that. If I were going to develop a unit from scratch, I might have it display "gallons to empty." Then, when you fill up, you back-calibrate it and it can figure out how fast your injectors are squirting fuel. Of course, some people smarter than me may have already figured out that it can't be done this way.

Last edited by scope103; 10-05-2014 at 12:12 PM.
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Old 10-05-2014, 01:34 PM   #7
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That doesn't sound like calibrating. More like giving the unit a standard to work with and then the unit just measures miles and extrapolates. That wouldn't account for any actual changes in MPG. I would LOVE to know on an ongoing basis what my MPG is, but if the unit isn't measuring actual fuel used against miles traveled, it isn't calculating anything, merely extrapolating from a FIXED standard. It probably needs an inline flow meter to actually calculate fuel used vs miles traveled. Am I wrong (there's a first time for everything) or do some of the newer autos have a MPG readout?
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Old 10-05-2014, 01:42 PM   #8
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How I understand it (I haven't fully figured this thing out yet) is that you can set the number of gallons your tank holds. Once the speed and injector settings are calibrated properly, it is theoretically very accurate in being able to sense how much fuel your injectors are using... and therefore how much it has left.

When you fill up the tank, you hit the left and middle buttons which is called "tank reset". The drawback to this method is that you can't do a partial fill up and have distance to empty work.

If you look at the calibration instructions on the ecomodder wiki maybe it will make better sense than I can explain it.

In the meantime, I'm trying to do some "easy" fixes to the car I had before my runner, I'm getting ready to sell it. It's an 05 scion xa. Having a devil of a time freeing the lower control arm from the hub assembly. I've probably been smacking it with a hammer for 2 hours. Earlier I replaced the PS and AC/water belts. I am so ready to be rid of this car, the engine bay is so cramped. It will be good riddance. Sorry, had to vent!
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Old 10-05-2014, 01:46 PM   #9
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Originally Posted by wireguy View Post
That doesn't sound like calibrating. More like giving the unit a standard to work with and then the unit just measures miles and extrapolates. That wouldn't account for any actual changes in MPG. I would LOVE to know on an ongoing basis what my MPG is, but if the unit isn't measuring actual fuel used against miles traveled, it isn't calculating anything, merely extrapolating from a FIXED standard. It probably needs an inline flow meter to actually calculate fuel used vs miles traveled. Am I wrong (there's a first time for everything) or do some of the newer autos have a MPG readout?
It knows how much fuel you are using based on the timing rate (sensed) and flow rate (user-set) electrical impulses from the injector sent to the ECU. Combining that with the speed sensor, it can extrapolate MPG.

So, yes, it is actually measuring fuel I agree, it would be rather pointless if it just based everything on speed.
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Old 10-05-2014, 01:56 PM   #10
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Sorry, I wrote this while others were posting at the same time, so there is some overlapping (but consistent) information.

The unit measures fuel flow by measuring injector pulse width. That's why it needs to be hooked up to one of the injector wires. The ECU recomputes injector pulse width for every engine revolution in response to throttle inputs, load, temperature, air flow, coolant temperature, and O2 sensor reading.

To a first order, fuel flow is proportional to rpm x injector pulse width. The unit can get rpm and injector pulse width by tapping into the injector wiring, and speed from the speed sensor. That gives the unit all the information it needs to calculate instantaneous fuel mileage, and by extension, average mileage and total fuel consumption.

However, as scope says, you need to supply it a calibration factor so it can accurately convert injector pulse width into milli-liters of fuel. That constant is different for every type of injector.

The program I published on this forum last spring uses data from the diagnostic port to do, among other things, much the same thing. However, it is useful only on '93 or later model trucks and 4Runners - earlier versions didn't supply the necessary data from the diag port. The unit jennygirl has found should work on any fuel injected vehicle, plus doesn't require that you tie up a laptop full time in your vehicle. Looks like a good find.

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Old 10-05-2014, 02:25 PM   #11
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I had one truck that if all I did was city driving, I got 100 miles less to the tank due to stop and ago and usually never got out of third gear. Next day I would do all interstate, 5th gear the whole way. That will play into your MPG as well and your 11 mpg may not be far off seeing as you live in LA and getting stuck in traffic.

Still it will show you how your driving habits really effect mileage and that can save you a ton of cash as you go.
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Old 10-05-2014, 02:27 PM   #12
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That's a neat little device, pretty much like a Scangauge but for older OBD1 vehicles
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Old 10-05-2014, 02:33 PM   #13
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The part some may be missing is that the pressure ACROSS the injector is always the same; the Fuel Pressure Regulator keeps the fuel rail at exactly 41psi above the pressure of the intake manifold. As a result, the ECU can control the amount of fuel injected simply by adjusting the injector open-time. If you measure that interval (and you know the liters/minute, which is now constant), you're measuring the amount of fuel squirted in.

Is it that simple? Well, almost. You'd think our injectors open once per two revolutions, right at the time the respective cylinder is starting the intake stroke. No such luck. The injectors open once per revolution (so twice per cycle), and they all open at the same time! The authors of the Arduino program, it seems, have already figured that out (of course, they're writing this software in 2008, for 14+ year old vehicles).
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Old 10-05-2014, 03:07 PM   #14
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Scope, that's some neat info. Do you have any idea why the ECU in my 87 has two ECU injector in lines? I.e. it is specified as No.10 and No.20 for return voltage lines going from the injectors to the ECU.

I tapped into No.10 for the MPGuino, and I found a post in their forum that said even if your ECU has more than one, you only need to tap one.

Why would toyota do this? There has to be a purpose
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Old 10-05-2014, 03:12 PM   #15
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i've always assumed it's just to spread out the current load required to pulse the injectors. The injector coils take a couple of amps per injector when they are pulsed. Doing all 6 with one wire takes a heavy wire and husky driver transistors in the ECU. A little easier if you break the issue in half.
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Old 10-05-2014, 03:12 PM   #16
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Originally Posted by Terrys87 View Post
I had one truck that if all I did was city driving, I got 100 miles less to the tank due to stop and ago and usually never got out of third gear. Next day I would do all interstate, 5th gear the whole way. That will play into your MPG as well and your 11 mpg may not be far off seeing as you live in LA and getting stuck in traffic.

Still it will show you how your driving habits really effect mileage and that can save you a ton of cash as you go.
Last night when I first test drove it (I haven't had a chance to take it out since as I've been hammering on this god forsaken car I'm trying to sell), it dawned on me that in lower gears your gas mileage is severely reduced. Only in 5th gear will you get anything close to reasonable. It shocked me that I had never really thought about that before, such a simple concept.
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Old 10-05-2014, 03:51 PM   #17
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... Do you have any idea why the ECU in my 87 has two ECU injector in lines? I.e. it is specified as No.10 and No.20 for return voltage lines going from the injectors to the ECU....
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i've always assumed it's just to spread out the current load required to pulse the injectors. ...
I think that's right. If I read the schematic correctly, 10/20 is divided between left and right banks. It may also be an attempt to reduce 'ground bounce,' but that shouldn't matter if they all fire at once.

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...I tapped into No.10 for the MPGuino, and I found a post in their forum that said even if your ECU has more than one, you only need to tap one. ...
That's true even if you have direct injection; each injector getting a separately timed pulse. For all except some '80s era Cadillacs, for every time injector #1 (say) fires, injectors 2-6 will fire, and for the same duration. So the calibration factor you enter isn't really the amount one injector squirts in per microsecond, it's the total of all 6.
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Old 10-05-2014, 08:17 PM   #18
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1- you can get an MSP430F5529, which can do most everything an Arduino can, for less than $15USD, but you might get stuck with voltage level translations... and considering you should be buffering the fuel injectors' pulses, that's a moot point.


2- measuring fuel injector pulse width is arbitrary, sort of. Fuel pressure changes in response to manifold vacuum, making any sort of inference regarding fuel flow based on pulse width inaccurate at best, and otherwise completely wrong.

That a forum moderator would support fallacy is disturbing, at best.


On the other hand, if you don't know these things already, you'd probably be better off not even attempting the things in this thread.

Last edited by abecedarian; 10-05-2014 at 08:20 PM.
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Old 10-05-2014, 09:11 PM   #19
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1- you can get an MSP430F5529, which can do most everything an Arduino can, for less than $15USD, ...
Even less http://www.ti.com/tool/msp-exp430f5529lp , but you still have to buy the display. And wire it all up. And program it (the arduino code is "open source," but for the MSP430 I'd be on my own). I'm a big fan of the MSP430. But it was worth the $68.50 (including shipping from ... Estonia!) to me.

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... 2- measuring fuel injector pulse width is arbitrary, sort of. Fuel pressure changes in response to manifold vacuum, making any sort of inference regarding fuel flow based on pulse width inaccurate at best, and otherwise completely wrong. ...
This, I don't get. Isn't the whole point of the FPR to keep the pressure ACROSS the injector constant, so the ECU can control FLOW just by pulse width?
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Old 10-05-2014, 10:49 PM   #20
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The teensy completely blows the arduino aout of the water in almost every way and only costs $20 for the really good 3.1 version. It even runs the arduino IDE if you want it to. It's about 32x faster clock speed, wider voltage input range, and tons of other features like bigger memory storage. But for some reason, I always go back to arduino.. I worked on a project a while back for a company and they had a bunch of leftover arduinos, so I guess that's why I use them so much. I have a stockpile of about 10 left that I got for free

In other news, calibration has begun! I just filled up the tank, took down the odometer reading, and hit the tank reset. Once I fill up again (at the same pump) I will be able to compare how many gallons the mpguino says I used against the gas pump amount and get my calibration values.

I did some highway driving tonight and my trip mpg was at 12.7 when I got home, can't wait to have this thing calibrated to know if that is for real or not! Yikes!
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