Pontiac Repair: 1990 Grand Prix stalled on highway and will not start, crankshaft position sensor, scan tool

Question
My son bought a 1990 Grand Prix from a private party a month ago.  It had been running rough at idle but fine under power on the road.  I had recommended that my son do a complete tuneup.  He called me the other day to tell me that the car died on the highway and would not restart.  He said that it stared running rough under power and he tried turning around and taking the car home but it died in less than a mile and would not restart.  I towed him home and we found weak spark, so we replaced all three coils, wires and plugs on the 3.1 motor.  At the end of the day it would still not start.  It cranks and when he lets off the starter it hits one more time and stops.  We can smell fuel after cranking several times and he has 1/2 tank of gas.  I'm thinking it is some type of sensor, but have no idea where to look next.  Thanks for any help you can give.

Answer
Well Greg, the first place I would suspect after all you have done is a crankshaft position sensor. This can be found on the back side of the engine down close to the oil pan. If you have access to a scan tool this is the best way to test for crank reference signal. The second thing to check is you didn't replace the ignition module with the coil packs and these go bad regularly. Finally even though you can smell fuel hat doesn't mean you have good pressure which for that motor requires 40-47 psi with the engine off and the key on before it will run. Start with these and if it stil won't start feel free to send another question to me. Hope this helps you and good luck.