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Old 07-21-2014, 05:58 PM   #1
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Default 1v difference between Pin 28 and indicated voltage?

I was troubleshooting some issues this past weekend and I noticed that the voltage coming in on the main board pin 28 is about 1v higher than the voltage I read from the 12v point on the ECU "header" (if that's what it's called).

Also, in Tunerstudio I noticed that the indicated voltage matches what I found in that header.

I decided to try and trace down what was reducing my voltage and I found that on one side of D10 (an n4001 Diode) the voltage matched input voltage and on the other side there was a drop. I got out a spare N4001 and checked how much voltage I read from a "fresh" diode and found it to be roughly the same.

Is this voltage difference something that is compensated somewhere in the programming? Reason I ask is that we have these curves for fuel injectors for example and they rely on the voltage that the ECU chip sees and it seems that the power supply itself is actually higher than indicated.

In addition, with the new alternator control code, I worry that keeping the battery at 14v (indicated on MS) really means the battery is being hit with 15v.

Is this not a big deal? Am I missing something?
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Old 07-21-2014, 06:01 PM   #2
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Finding links... Maybe answering my own question.

Megasquirt MSEXTRA / MS3EFI • Battery correction. THe correct procedure? (View topic)

Looks like I missed the battery voltage correction stage of my set-up.

I love megasquirt, I don't love the confusion regarding set up.

Last edited by Chiburbian; 07-21-2014 at 06:15 PM.
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Old 07-22-2014, 11:11 AM   #3
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They are working on a pretty big documentation overhaul. What MS variant do you have?
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Old 07-22-2014, 11:13 AM   #4
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Quote:
Originally Posted by Chiburbian View Post
Is this voltage difference something that is compensated somewhere in the programming? Reason I ask is that we have these curves for fuel injectors for example and they rely on the voltage that the ECU chip sees and it seems that the power supply itself is actually higher than indicated.

In addition, with the new alternator control code, I worry that keeping the battery at 14v (indicated on MS) really means the battery is being hit with 15v.

Is this not a big deal? Am I missing something?
youre supossed to meter your voltage at the injectors.

calibrate your battery voltage in software so it matches your reading at the injectors.

most installs will read low because probably 1% of MS users here with the option have probably actually gone out and done it.
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Old 07-22-2014, 12:42 PM   #5
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What is your favorite source for MS start-up procedures? I am thinking of creating a new project and starting over.

Specifically I am looking for something that is a guide step by step of all the things you SHOULD do, in what order. I am not too concerned about in depth stuff as long as they point to the proper current way of doing things. Does such a thing exist?

So many cars run on Megasquirt, indeed mine does. I am just a little frustrated by all the problems I am having based on improper stuff I did earlier on. Too much rework, too much tweaking. I feel like often I am making adustments to fix a fundimental error I made early on in the process and instead of fixing the problem I am compensating for it. The voltage thing is an example.
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Old 07-22-2014, 01:11 PM   #6
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i dunno. ive forgotten more than many people even learn.
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Old 07-22-2014, 01:54 PM   #7
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Matt - MS3x, Mapdaddy4, real time clock, knock board, EBC, Alternator control in software (as opposed to dedicated board).

Alternator control is what brought on my troubleshooting. I traded emails with you in regards to Mapdaddy malfunction and a new one should be on the way any day now.

Once the Mapdaddy arrives it's all getting reassembled and installed with my current tune with hopefully functioning alternator control. If that works, I will likely freeze work on that tune and start a new project and then be able to swap back and forth if I screw something up.
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Old 07-23-2014, 11:07 AM   #8
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I would start here.

Megasquirt MS3 First start

If you have any suggestions on things that need to be added there, let me know.
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Old 07-23-2014, 01:00 PM   #9
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I would start here.

Megasquirt MS3 First start

If you have any suggestions on things that need to be added there, let me know.
How would one determine Max ADC and Min ADC for battery?

Would you just keep the MIN at .1 and raise/lower MAX ADC until your voltage indicated on MS/TS matches what you get at the injectors?
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Old 07-24-2014, 10:44 AM   #10
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That should work well as long as the MS is grounded properly.
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Old 07-24-2014, 11:45 AM   #11
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Why is there so much difference in voltage between where MS senses battery voltage, and the injector lines?

In the miata factory ECU there are 2 places battery voltage comes in. One of them is where the injectors are connected in the wiring harness....
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