Engine starts but dies after a few seconds

Hi guys. I have a 1994 Jeep grand cherokee laredo 4x4 6cyl. I just recently bought this jeep it ran then it wouldnt start then ran fine again. I did a tune up of plug wires, plugs, cap, rotor, coil, pick up coil, crank sensor. It ran fine for a day and wouldnt start after that. Fuel pump works and great pressure. Relays are all good and the same with the fuses. It would crank over but no spark to the coil. Then we found a used ignition control module {brain box} from the same yr. Model and options mine has for $35.00 and not $650.00 new. Now it starts up but dies a few seconds after like I turned the key off. Still good fuel pressure and relays. It has a security system but I dont know how it works. Im kinda lost now. Any ideas? Thanks guys!