In the early 90s, when ECUs were just becoming a thing, my colleague, who was a weekend rally driver, plonked one on my desk and asked if I could figure out how

In the early 90s, when ECUs were just becoming a thing, my colleague, who was a weekend rally driver, plonked one on my desk and asked if I could figure out how it worked and, if possible, to tune engine parameters for maximum performance. I identified the microprocessor as a 6502, based on board topology, even though all IC markings were removed. At the time (before the internet), I could not find a 6502 disassembler, so I wrote my own. I successfully decompiled the code, figured out how it worked and found the parameter "maps" stored in ROM. Loaded these into Matlab and wrote scripts to allow my colleague to tune the maps and write them back to EEPROM. It was a couple of weekends' work for me, and I never thought about monetizing the knowledge. Several years later, I met another colleague who did the same for the Mazda RX7 ECU, and made a tidy side income selling "performance ROMs". C'est la vie.