I bought a 2004 545I with a blown engine due to the owner constantly driving it with a misfire in cylinder 6. I had my mechanic put a new engine in but this engine misfired on cylinder 6 also. He tore down the engine said he found that the injector was bad and cylinder was flooded. He cleaned it out changed the injector and the engine ran okay. The warning lights went away and there were no more codes. After only a few hours of having it parked my mechanic started it and once again the engine began misfiring. any ideas... any help would be very much appreciated.