Help 1994 Buick Regal Custom 3.8 l

[lady dee]

Hello I have a 1994 Buick Regal Custom 3.8 l . I lost power on the interstate and it would crank but not start. Had it towed . Found out that the serpentine belt was chewed up by the crankshaft. When that happened it damaged the alternator severed some wires on the ecm damaged the crankshaft position sensor. I replaced all 3 coil packs, crankshaft position sensor, plugs ,wires , new alternator,new battery , repaired the damaged ecm wires , serpentine belt , and the harmonic balancer. It starts now but it shuts off almost immediately after starting. I also changed the fuel filter and the fuel pump is engaging . I am at a loss of words I don't know what else is wrong. Please help me any advice or similar stories of experience would be a blessing.