Car will not start
 

Hello everyone so here is a bit of background. I picked up 2 audis 2001 a6 2.7t both of them same engine same transmission codes. One is a good body bad transmission with 200k, the other is crashed body good engine and transmission 100k so I swapped both engine and transmission in the good body a6 now everything bolted and plugged in I used the ecu from the original body the car won't start now. I checked fuel it has fuel I checked spark it has spark air works. I checked the timing the belt jumped a tooth I straightened it out best I could withought a bar the cams are straight. I'm getting a backfire now almost every time I try to start. This was a hell of a job and I'm planning on keeping this car for my wife I would like to keep this 100k engine but I can always swap to the 200k. Also I had both engines running before I started the job. So I know the engine runs now I guess it's common for these engines to jump a tooth after sitting for a long time so I'm stuck any help would be appreciated. So to recap has spark has fuel has compression has air maybe I don't think the intake is somehow clogged in the 3 days it took to swap from one to the other.