c7 acert no start tons of smoke

problem started when truck came in to change sensor harness ( truck was running ). Changed the harness and truck would not start. It will barely run for about 5 seconds and then die. there are no codes and I just changed the fuel return regulator. So the truck has 900 psi while cranking, 70 lbs fuel psi and huei % is about 50 while cranking and when it is barely running it goes up to 89%. don't know what to do! :Banghead