Thread: I can't diagnose what's wrong with my car

I have a 1995 Pontiac Grand Prix with a 3.1 motor. I have been having trouble lately with my car shutting off. I turn my car on and can drive for about 20 minutes but then it starts to shake a little and wants to die. I have noticed that the car starts to overheat when this begins to happen. I try to turn on the car after this and it sounds like i wants to start but doesn't. When the car dies the battery still turns on. Also when it dies the battery light and oil pan light come on. I have taken it to my mechanic and every time I go it's something new. So far they have replaced the fuel pump, alternator and battery, and the cars computer. I have no idea what it could be.

I'm going to replace the crankshaft sensors. Do you know where I can find a diagram of a 3100 motor for reference? Also I notice that sometimes the security light comes on and other times it doesn't. Do you think that could be causing the problem since the computer was replaced?