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The mega have no issue but teensy mustn't be powered by both sources. There is a section on pjrc site explaining how to mod cable or teensy to ensure correct operation

No worries. Life gets in the way. A lot. See yo[…]

STM32 development

So here's a little update on the subject of my pas[…]

NO2C crank signal issues

Also sometimes when i turn the ECU off it seems to[…]

I don't think there can be another cause - it'll b[…]

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