How the 4A-GE ECU works

[firehawk]

Wow, this is VERY interesting! I've always thought that engine control systems are the most exciting part of tinkering with cars as they combine three of my favourite hobbies - cars, coding and electronics. It's amazing how many possible correction factors the 4A-GE ECU calculates over the initial density value - I've been playing around with MegaSquirt quite a lot lately and it actually seems rather simple when compared the original ECU. It should be quite interesting to see if it's possible to mimic the original ECU's mapping on the MegaSquirt - well, as soon as I have an engine to connect to it instead of just the distributor and an oscilloscope.

Do you have, by any chance, the pin assignments from the firmware on the microcontroller? A friend and I have been toying with the idea of pulling the controller off the 4A-GE ECU, replacing it with a socket and building a piggyback board which mounts onto the socket. The piggyback would use the 68HC908 and run MegaSquirt'n'Spark-Extra code so it would be easily programmable with existing tools. This would make an ultimate DIY plug'n'play solution for re-mapping 4A-GE ECUs - no need for tearing the engine wiring loom apart or butchering the original ECU for sockets.