I have this working, with the DonnerTech turbocharger, on the latest release of MSCLoader at the time of writing (1.2.12-291) and with the latest MSC version from Steam.
To do this, I used the June 2020 build of this ECU mod (09 Jun 2020, version 1.3.1, see the history tab.)
Edit: to be clear, this isn't the latest version of the mod. The fuel injectors aren't in this version for example, nor the chip programmer. Still, nice mod to have, has most of the modules and the display works nicely. Plus cruise control introduces entirely new hazards to the game lol.
I installed the latest DonnerTech Turbo mod long ago, but here is what I did after that. If you havn't installed the Turbo mod this method probably ain't gonna work for you, allthough I didn't test it so who knows.
1) Make a backup of your mods folder and your save, and don't cry here if you didn't and now the game crashes lol
2) Install the latest DonnerTech Turbo mod, if you havn't allready, and start the game, checking the repair shop to make sure it is installed and working correctly. Then shut down the game.
3) Install MscModApi v1.0.4 into the Mods folder, there should be no conflicts.
4) Drag and drop the contents of the 1.3.1 ECU mod, and choose to keep all files currently in the Mods folder for conflicts (don't overwrite the screwable API, the modapi_120-alpha, the modsshop dll, or shopassets.unity3d)
5) voila now you can buy the parts in the repair shop in the same catalog as the turbo.
I may fork the repo and modify the code to use the old shop api someday, should be possible but I havn't got any of the dev kit installed on this rig, and I'm happy with the current stuff since the turbo mod alone gives more than enough power to pound my pistons through the oilpan and into the asphalt lol, don't really need injectors at the moment.
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Just wanted to say, thank you for your work on these mods over the years DonnerPlays, I have gotten hours of enjoyment from these mods and blown the satsuma up with them more times than I can count lol. Hopefully this can at least get some of the people in this thread going and it can be more peaceful here