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Embedded Code for Your MicroSquirt® Controller

Your MicroSquirt® controller comes with the embedded code already loaded onto its processor. You can still upgrade to newer versions of the code as they are released, of course, but you won't have to load the code initially to get your MicroSquirt® controller working.

The current 'release' code for the MicroSquirt® controller is V3.830b.

The 'ready to load' .s19 file for uploading to your V3 MicroSquirt® controller is here:

(Right click and 'Save As')

For the V3.830 code, you will also need the megasquirt-II_3830.ini file. Do NOT rely on the INI that comes with your tuning software, even if it has the correct version number it may be out of date and not have the latest updates and corrections.

The help file for this code is here:
This help file contains information on the tuning parameters and datalogged values in this code.

To load the .S19 file above to your MicroSquirt® controller over the serial port, you use Eric Fahlgren's downloader program (click the link to download). This application installs much like any other Windows application. 'Run' the download when prompted, and follow the instructions.

To use the downloader.exe application to load code to your MicroSquirt® controller:

  1. Save an MSQ setting file of your existing setup.

  2. Power down MegaSquirt® EFI Controller,

  3. Ground the bootloader wire (Ampseal pin #15).

  4. Power up your MicroSquirt® controller.

  5. Start the downloader program (make sure TunerStudioMS is not running), and select the appropriate COM port. Note that 'File/Update' does not work on the downloader to fetch the latest code and INI anymore. You can get the latest code and matching INI from this link:

  6. Select the appropriate .S19 file using 'File/Open', and the downloader will read, write and verify the code to the processor in about 10 seconds or so. If you have a problem connecting to the controller, see the tips here:

  7. The process ends with a message like "Verification succeeded, 999 records total (4 skipped)."

  8. Shut down the downloader program.

  9. Remove power from your MicroSquirt® controller.

  10. Remove the bootloader wire from its ground connection.

  11. Start the tuning software (TunerStudioMS) and set the COM port and speed if necessary.

  12. You will need to download and activate the latest INI file. Under the 'File/Project/Project Properties' of TunerStudio, click on the Other check box.

  13. Click the 'Browse' button.

  14. Locate the INI file you downloaded for the link above (

  15. Click on the appropriate INI file you download from the code page ( to activate it.

  16. Finally, reload the MSQ file (aka. 'tune') you saved above, paying particular attention to any warnings the tuning software gives you (these are generally for settings that have changed or been added to the newer code, so look them up in the help file and decide how they should be set).
If you have changed code versions, you should recreate your settings file (aka. 'MSQ') from scratch by entering the values by hand into TunerStudioMS.

V3.830 has the following improvements over earlier code:

See the 3.8xx code help file for more information: mt38.htm

MegaSquirt® and MicroSquirt® controllers are experimental devices intended for educational purposes.
MegaSquirt® and MicroSquirt® controllers are not for sale or use on pollution controlled vehicles. Check the laws that apply in your locality to determine if using a MegaSquirt® or MicroSquirt® controller is legal for your application.
©2013 Bruce Bowling and Al Grippo. All rights reserved. MegaSquirt® and MicroSquirt® are registered trademarks. This document is solely for the support of MegaSquirt® boards from Bowling and Grippo.