the ecu does not need modifying to output the datastream (except P8 that was not used in sierra's), only the run program in the chip.

i also cannot understand why the code is not publically available by now. it was originally developed by pectel, now PI, and i have heard that they like to legally protect their Intellectual Property.

having said that, i know that it has been cracked and that motorsport developments sell software that was developed by RP Lab to read the datastream into a PC. collins also sell a monitor to read the datastream (similar to the original rally Pectel monitor, not to be confused with SECS monitors that just tee into the ecu inputs and do an analogue to digital conversion rather than using the conversion inside the ecu).