Arduino Economy Computer

spitsnrovers · Posted: Fri Apr 15, 2011 7:01 am Post subject: Arduino Economy Computer

So as not to hijack rumitcu's thread on his great battery monitor using an Arduino, I've copied several posts from that post to start this one.

spitsnrovers wrote:

Volksaholic · Posted: Fri Apr 15, 2011 7:48 am Post subject: Re: Arduino Economy Computer

Spinal Tap · Posted: Fri Apr 15, 2011 8:51 am Post subject:

Yes, the Digijet/Digifant pulse ALL 4 injectors at the same time. I know GM's ECU's ran a PWM signal to the injectors at a fixed frequency, varying the pulse's width to modulate fuel delivery. If you look at the video posted the other day, it looks like Bosch did the same thing (or maybe GM did the same thing as Bosch).Video is in this thread. It looks like a fixed frequency, but I'd throw a scope on there to be 100% sure.

But I guess that doesn't really matter, PWM vs Frequency, you just need to know the amount of time the injectors are on. Most uControllers have timers that can be interrupt driven.

So you'd have to measure the ON time, and accumulate it, multiply that by the injectors CC-of-fuel/unit time, to get the amount of fuel going into 1 cylinder. Multiply again by 4 to get all the fuel going in. This will get you pretty close, but error will be introduced by the fuel regulator, since that is partially controlled by manifold vacuum, the pressure that the injectors see is not constant. But you should be pretty darn close, as they say, close enough for government work. Smile

This, by the way, is how it's done by automakers (BMW and it's vacuum/economy gauge not withstanding).
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r39o · Posted: Fri Apr 15, 2011 9:13 am Post subject:

DUH! I understand!

The trick is the time measurement. It is actually (almost) frequency independent. (Almost because you need to measure fast enough.) You just want the on time. What you are trying to do is make a computed flow meter.

If you have constant pressure and know the flow rate of the injector, you know how much fuel. When you have your injectors cleaned, you get a nice chart of flow rates. In other words, old injectors will cause errors.

Now you got to worry if you can code your controller timers well enough so you can capture time with out errors introduced in the interrupt service routine.

I just can not guess how close you will be.

FYI: I have seen commercial flow meters that are put in line with the system feed line to measure the flow.

This is a neat exercise, but can you tell me why you want to do this?
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spitsnrovers · Posted: Fri Apr 15, 2011 9:14 am Post subject:

Thanks guys.
Checked the Bentley and found pin 12 is THE wire to the 4 injectors, with pin 14 being the common return.

Yes, the VSS unit on the speedo is a 2 wire system. But the Arduino needs only 1 wire for signal, so hope that works.

Spinaltap, The computations you gave should be able to be worked into the Arduino set up. Work won't start on testing and installing till sometime after June 1st.
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r39o · Posted: Fri Apr 15, 2011 10:10 am Post subject:

Use a O-scope to check the signals. I don't know what sort of signal conditioning your controller requires.

I am a PIC / ARM / Atmel person and hence am a bit more deeply embedded looking at things.
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"Use the SEARCH, Luke" But first visit the Vanagon FAQ!

1990 Multivan EJ 22, Rancho trans 0.82 4th, Small Car front AC, CLKs w/ 215/65-16, homemade big brakes 303mm, Konis, Recaros, etc....

Click to see my ads for Cup holders, Subaru clutch fix and CLK wheels (no wheels currently)

edgood1 · Posted: Fri Apr 15, 2011 10:52 am Post subject:

The way I did it with arduino was to use one of the chip's interrupts to count the number of times the injectors fire every cycle of main loop inthe sketch. Ofcourse you need to have accurate timing of the cycles, but it works ok.
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Spinal Tap · Posted: Fri Apr 15, 2011 11:35 am Post subject:

r39o · Posted: Fri Apr 15, 2011 11:42 am Post subject:

Maybe, just maybe, there is an rpm or load related indication you can get in real time. Great. Great if that helps. Maybe you can see things better in real time than on a per tank basis. Fine.

I can think of LOTS of other things the processor can watch that would make a real world difference in real time. Better dynamic oil pressure monitoring. Real coolant temperature (or close to it,) other voltages or, perhaps, charge current. Stuff that can ruin your day if something happens. But, that is just me, I guess....

Keep having fun!
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"Use the SEARCH, Luke" But first visit the Vanagon FAQ!

1990 Multivan EJ 22, Rancho trans 0.82 4th, Small Car front AC, CLKs w/ 215/65-16, homemade big brakes 303mm, Konis, Recaros, etc....

Click to see my ads for Cup holders, Subaru clutch fix and CLK wheels (no wheels currently)

tilstad · Posted: Thu Oct 10, 2013 9:12 pm Post subject:

I know this is an old post but.... Perhaps someone else is reading it. On the 1987 VW Golf GLI, which is the convertible in Europe, there was a small flowmeter installed on the fuel line running to the little in-dash clock/computer, which among other things displayed fuel consumption.

Just thought I'd mention it, as that could perhaps be another route to achieve the same.

ohhorob · Posted: Fri Oct 11, 2013 12:14 am Post subject:

spitsnrovers · Posted: Fri Oct 11, 2013 6:44 am Post subject:

Great to see the renewed interest. I had put this project in the Too Hard basked, but will have to revive it again. I guess the truth is I'm scared to get involved with the wiring of the ECU. Confused

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tilstad · Posted: Fri Oct 11, 2013 7:55 am Post subject:

I wonder if that Golf computer/clock could have been substituted for the vanagon digital clock. They were about the same size. Then again, it's quite some time ago I had a Golf like this, so I can't vouch for a good fit.

It did have a stalk though, with various buttons on it.

I believe this is how the cluster looked like, and based on the symbols I guess one could assume the functions of it. I seemed to remember it did dual trips aswell.

Image may have been reduced in size. Click image to view fullscreen.

denwood · Posted: Fri Oct 11, 2013 10:39 am Post subject:

The older VW trip computer (had one in my 84 scirocco) fuel mileage computer calculations are based on engine vacuum, so reasonably accurate but not nearly as precise as measuring fuel flow via injector duty cycles. Recent fuel mileage add ons are using this information via ODBII, so will not work on the vanagon. The reason you don't see flow meters installed is the fact that as mentioned, you would need two and enough intelligence to provide the difference between the two. The fuel pump runs 100% duty cycle, and any therefore any excess from the regulator is returned to the tank via fuel return.

I did a fair bit of reading on the topic of late, so simply installing a vacuum gauge to monitor will change your driving habits. Injector pulse, and some intelligence is the best way to monitor fuel flow...and being that we don' have ODBII, I would be all over this project using Arduino Smile

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