this got me thinking yesterday, so I'm going to throw out some thoughts and questions, I'm unsure of how stand-alone the OE ECM is, and what it requires from the engine to run, but maybe one could just use the factory ECM, but not the whole harness from the car? (assuming it's going into a mk1 or mk2, my application would be mk1 if I attempted an electronic control vs TDI-m)
The solenoid controlled VW pumps (I believe that's what the TDIs use, AHU/1Y, anyway)
have a single solenoid to control injection events on all 4 cylinders. So only a single injector driver would be needed. Most of it is still mechanical like the IDI pumps, just that there's a solenoid to control the flow from the high pressure to the plunger to the injectors.
If one could hook a datalogger up to the solenoid, as well as find out crank angle, you may be able to find out what the injection event looks like based on crank angle and cam angle and stuff.
there's alot more questions in my head, but right now, I'm not so sure running a megasquirt is impossible if you can get injection event duration under control and running at the right part of the crank position, which can be roughly figured out with datalogging a running, OE TDI.
but it's not needed if the things the ECM needs are minimal and can be run without using the entire cars harness, and just a few external sensors, etc are needed.
I'm unsure of how integrated VW has made the ECM into the rest of the car, if it needs stupid things like if the ABS is working or not, or whatever, it won't work.
wouldn't it be possible to program an ecu to make the electronic pump just run a program without sensors? it would theoretically be like running a mechanical pump... just the ecu connected directly to the pump... wayyy less wires!