So in general ECU's are not easy to just wholesale replace as they may have safeguards built into other electronics looking for proprietary signals from the ECU

So in general ECU's are not easy to just wholesale replace as they may have safeguards built into other electronics looking for proprietary signals from the ECU to activate. You can reprogram aspects of an ECU pretty easily, and you can even clone an ECU. But as far as just replacing it with a non-OEM ECU, I would think it would be cost prohibitive to do the research and development needed to do it properly. This is especially true of higher end cars, where the ABS computer, Radio, Transmission Controller etc all are usually separate and require signals from the ECU. You could reverse engineer it again, but time isn't free. There are specs you can find on ECU's, most are SAE specs, and most late model ECU's use CAN bus for communication. Sparkfun has an article that talks about reading diagnostic codes etc and shows a list of most specs, although I don't think it is comprehensive. https://learn.sparkfun.com/tutorials/getting-started-with-obd-ii https://learn.sparkfun.com/tutorials/getting-started-with-ob... Aftermarket companies that sell "chip" tuners, from what I understand, work by first using the known protocols to gain access and tune what is possible, but then also will either pay the OEM for access to make other modifications (and thereby usually be covered under factory warranty), or they will reverse engineer things like the fuel map so they can modify it, which works but isn't so warranty friendly.