1989 Pontiac 6000 starts then stalls

Just bought the car. Told that it was an electrical problem, has fuel pressure at 40-45 psi. Has spark at each plug, changed plugs, new battery two days ago, had the alternator tested yesterday. Can hear fuel pump buzz when key turned on, checked OB1 codes just throws the number 12. Looks to have new coil packs, the plug wires are correct. New radiator with hoses, has been sitting for a about a year. The fuel tank is full of fuel. Starts then stall instantly.