How the 4A-GE ECU works

[JMR_AW11]

firehawk Wrote: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.

Already done it.

I made a PCB which replaces the original 40 pin ECU microcontroller but it supports the original factory ROM code and maps. It allows access to all the factory maps and the rev limiter and TVIS etc.

The stock ECU has a hidden diagnostic capability which I modded and it allows me real time remapping on the fly with the engine running by using my modded ECU.

I also modded the fuel mapping to a full 3d system. In other words I binned the 2d speed and density maps and replaced them with a huge 3d map. I also increased the mapping to cover up to 8400rpm (21x10 map) for both fuel and ignition.

I'm writing a user interface for this modded ECU which allows point and click remapping in real time with the car on a rolling road.

The remapping GUI is quite good to look at.

I released a demo version of it last Summer to see what feedback I got.

The real version has had a few upgrades since the demo and I tested it out for real on a rolling road last year.

See

http://www.jmross.freeserve.co.uk/demo3d.html

if you want to download the demo.

The demo only covers the main 3D maps. The full version has lots of other maps to play with...

HINT press the little yellow AUTO button on the demo to see how the SITE TARGET indicator works.

BTW
The original ECU has over 40 lookups in it. My articles only cover the main maps. It is quite a complicated ECU for its age. The other maps affect the throttle response and overrun and warmup. These little maps are tailored to the 4A-GE and this is why the stock ECU keeps the 4A-GE engine running so sweet.