I have a 2000 S80 that ran fine until I put a new radiator and AC condenser on it. I also removed the oil pan to have a crack welded. Now it starts but dies almost immediately. Anyone have any suggestions to try? Thanks in advance.

 

Sounds like you left something off; like an air hose, or left some electrical plug unplugged. Go back and double ck everything you touched.

 

+1 with GDog. Also check to see if you maybe knocked something else loose.