Hi, I just recently purchased a 2006 Audi A4 Quattro 2.0T. I got it for very cheap since it does not start and I enjoy fixing cars at home. My diagnosis so far is either the starter motor or the relay for the starter motor. The battery is extremely dead so I had to hook up a booster pack to try and turn it over. When I turn the key I can hear the fuel pump engage and the motor cranking over super slowly??? I have a pretty good knowledge of cars and working on them but I cannot seem to figure out this one! Hopefully you can help me diagnose the problem so I can go ahead and fix it!
The battery may have an internal short. This could cause an issue with the booster pack. Install a known good battery and fully charge it before furthering your diagnostic testing.
2006 Audi A4 Quattro 2.0 Starting system wiring diagram