how to convert afr target scale from volts to afr

[yunvmyegt]

i dont take any credit for this aside from copy/paste to here, but i still see people talking about volts on here so i had to post this. i set up mt when i was using it and tunerstudio this way, it takes only a few minutes to rid the volts values

thread is located here

http://www.miataturbo.net/showthread.php?t=28005

This has been posted before, but comes up often. So I'm putting all the info in one place and adding it to the Super Important sticky.

By default, if you select "AEM Linear" in the MegaTune Configurator, your AFR Targets table is scaled to volts, and you must reference the AEM documentation to find the correct values. You can change this so that your AFR Targets table is scaled properly in AFM instead.

First, go into the \Program Files\MegaSquirt\MegaTune2.25\mtCfg\ directory, and open the file msns-extra.ini in notepad.

Scroll down until you come to a section labeled
page = 7 ; TARGET AFR table 1 BINS FOR VE 1 (First find which sensor used)
This is to ensure that we're altering AFR Target Table 1, which for most folks is the only one in use.

Look for the following lines in that section:

#elif AEM_LINEAR
afrBins1 = array, U08, 0, [8x8], "Volts", 0.0196, 0, 0.0, 5.0, 2

You want to make the following changes, which I've highlighted in red:

#elif AEM_LINEAR
afrBins1 = array, U08, 0, [8x8], "AFR", 0.038666, 255.0, 10.0, 20.0, 1

If you wish, you can just copy and paste the second line into your file.

The next time you open MegaTune and look at your AFR Targets table, you'll find that it is scaled in AFR rather than Volts. The contents of the table will be garbage so if you already had values in here you'll need to re-create them, but from now on you can work in meaningful units.



Now, a lot of folks have reported problems with the default calibration, in that it can be a few tenths out in terms of the MS agreeing with the AEM. It seems that there is some variance from one AEM unit to the next. If you find yourself in this group, you can correct it by opening up the file file "lambdasensors.ini" which you'll find in the same directory as before. Locate the following section, and note that I've highlighted a certain pair of values in red:

#elif AEM_LINEAR
afr = { 9.72 + egoADC * 0.038666 }
lambda = { afr / 14.7 }
TargetAFR = { 9.72 + afrtarget * 0.038666 }
TargetLambda = { TargetAFR / 14.7 }

To alter the calibration, you need to change the 9.72s to something else. And this, sadly, is where the fudge factor comes into play. Some people have reported success in scaling the value up (to 10, for example) others report needing to insert lower values (9.5, in one instance). You're going to have to play with it and see what works. Just turn off EGO correction and eyeball the laptop display vs. the gauge at idle. Find a value that works for you.



Sources cited in compiling this info:
forums.plastikracing.net :: View topic - MegaSquirt Tips and Tricks
forums.plastikracing.net :: View topic - Fixed algorithm in Megatune for the AEM UEGO
MiataTurbo.net :: View Topic - For those using AEM Linear with MS



Addendum:

A lot of folks have been reporting trouble with this. It seems that all these folks have non-standard Megatune installs, wherein there are multiple copies of the msns-extra.ini file in various locations.

If this is you, then you need the find the one that's actually important. My guess is that if, when you open MegaTune you are presented with the "Select a Project" window, then you need to edit the copy of msns-extra.ini in the appropriate Project folder, and not the main one.

As an example, I installed the MSPnP software package, and I now have six project folders, two each (with and without AFM) for 9093, 9495, and 9697. If I edit the one in C:\Program Files\MegaSquirt\MSPNP MM9093 without AFM then I see AFR as units when I start MegaTune and select that project, but if at startup I select the "MSPNP MM9093 with AFM" project, I see units in volts.

So check that.