Click on our menu buttons immediately below to find MegaSquirt® information quickly:

MS-II Downloader v2.00

The MS-II™ downloader by Eric Fahlgren now includes a "package browser", which lets the user pick a package site and grab the latest updated code/ini files directly via the GUI downloader, and the downloader will automatically update both MegaSquirt® and MegaTune with the right files.

You can get the V2.00 Downloader here: ms2dl200_setup.exe

Install the program like any other Windows application.

To do a code and INI update:

To load a 'ready to load' .S19 file to your MegaSquirt-II™ over the serial port, you need to use Eric Fahlgren's MegaSquirt-II downloader program (click the link to download), which works from either a window or from the command line.

To use install new code using the downloader.exe:

  1. Power down MegaSquirt® EFI Controller,

  2. Put the boot jumper on both pins of the header marked B/LD (for "bootloader") on the MegaSquirt-II™ (not the main board), (on MicroSquirt® controllers, ground the bootloader wire)

  3. Power up MegaSquirt® (plug in the stim) or MicroSquirt® controller. The LEDs on MegaSquirt® will flash very briefly (if installed), then go out. This is proper response for the LEDs when the MegaSquirt-II goes into bootload mode (i.e. when the bootload jumper is on).

  4. 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:

  5. 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:

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

  7. Shut down the downloader program.

  8. Remove power from MegaSquirt® (disconnect the stim) or MicroSquirt® controller.

  9. Remove the boot jumper (or put it on just one pin of the B/LD header for storage),

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

  11. 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.

  12. Click the 'Browse' button.

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

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

Command Line Downloader

The downloader also has a command line version (ms2dl.exe) included in the package. You can run the command line version in a script, so if you have makefiles or something of the sort, you don't need to interact with GUI version at all.

Look in the downloader installation directory (typically 'C:\Program Files\MegaSquirt\MS Download 2.00') and you'll see ms2dl.exe, which can be invoked from the command line (or .bat file) like this:

ms2dl -c3 -r115200 something.s19


("ms2dl -h" gives you a usage message.)

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.
©2004, 2012 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.