Car wont start

im still waiting for an answer friends

If you disconnected the batt. a memory saver may have been needed , Something else may have gone wrong by pure coincidence , you go about this same as any no start scenario , check for proper spark , fuel pressure , injector pulse , I don't know anything about bmw's there may be some kind of over kill tech on them for sure so who knows what's up . You're the owner of one that just did some serious mechanical work on it maybe you should know .