Originally Posted by
bill g
The 530i ECU will have ignition timing and fuel mixture maps specifically for that engine. Your engine may seem to be running OK with the swapped ECU but could be running lean or over-advanced which will cause damage to the engine. Maps are usually programmed onto a chip in the ECU. I do not know whether either of those particular ECUs have removeable chips and if they do, whether the chips can simply be swapped over. For all I know they may have the exact same chip in them. You really need to investigate this further - anyone else got more specific info?
Bill G