hey I just replaced my engine in my 07 q7 4.2 with a used one put everything back in and went to start it but no spark and no fuel when I spray starting fluid it runs for a few seconds then dies out. I manually gave power to the fuel pump because there was no power there and when I did it started up and ran fine for a min or two. could it be the crank sensor or do I need to reprogram the computer even though when I took the engine out I put the same one back at the end? please help