1990 Other Chevrolet Models

Could you explain to me when you say the oil pressure switch came apart? I am thinking that that the computer is picking up a false signal. You cand try to reprogram the computer by taking it in and have it professionall;y reprogramed or you can try to disconnect the battery circuit and leave it off for as couple minutes then reconnecting. This way when you start it will pick up correct codes. The oil pressure switch may be not sending a signal to the engine that you are not getting oil pressure and shutting down the engine. Check the connections on the switch to make sure they are clean and dry.