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E30 ECU variant programming specificity between manual and auto cars

May 22, 2024

Counter to popular narrative on E30 forums (based on self perpetuating hearsay), there are variant code differences between manual and auto E30 ECU’s and M1.3 didn’t always post date M1.1 ECU’s.

The bad news is that no tuner has a fully disassembled dump of the ECU source code. Most just take the post compiled HEX output and change known sections of code (to gain performance by changing maps and ignition timing).

The short answer is that generally M20 E30’s seem to run fine with Auto or Manual ECU’s swapped between them, but we have no way of knowing if there are subtle differences short of Bosch or BMW providing the full decompiled source code.

Most critically, when buying ECU’s from overseas its important to keep note that variant codes also dictate the presence of an O2 sensor and so swapping in an ECU with an incorrect variant can and will disable O2 sensor data processing.


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