From responses I have received, Coil pack and crank shaft sensor most probable cause. Mechanic will run through a number of standard tests. Might show up something

 

When car won't start, PCM scanner shows "No Communication" message. Also fuel pump does not hum when ignition switched turned on. My guess is defective PCM. Does this make sense. Should I change PCM?

Brint

 

Problem was resolved by changing computer. When Lumina would not start, computer would not communicate with OBD scanner. Also wiring diagram shows fuel pump relay controlled by output from computer only. Only mystery is how engine runs ok once started even though computer has failed. What conrols the fuel pump?