This was my whole point, you seem to be having problem which you say are related to software but instead seem to be car/interface dependant.

If you connect the 12V pulses from the ECU to the DTR line on the empeg's serial port, the hardware is finished. Then you just count pulses on DTR. I agree that OBD would be more flexible but I disagree that it could possibly be any easier.

The only car specific part would be finding the correct lead into the ECU. PIN A1 (Green/Yellow) on a WRX by the way.