Cadillac: 98 Catera Intermittent System Failures, fuel pump relay, crank sensor

Question
My 98 Catera is having issues.  Since Thursday (07/05/07) the vehicle completely shuts down while I am driving.  The unexplainable is that I maintain all of my electrical system (Interior lights, radio, etc...).  However, when the vehicle stalls, it just completely shuts down.  I had it to the mechanic this morning thinking that it might be something electrical.  However, they said that it is not.  I took it to a dealer, they ran a diagnostic and repeated the failure, however they could not tell me what the problem is.  Could you please help???  I am not sure if it is the fuel pump, fuel pump relay, or the crankshaft positioning sensor.  All three of these items could cause the failure...can you please provide me with a way to determine what the root cause is before I spend 600.00 or more on a solution that is not the real answer????

Answer
If it was the crank sensor you would get a CHECK ENGINE LIGHT on the dash.

The fuel pump relay is ONLY used when stsrting the engine.

Any electrical sensor fault would also produce a check engine light.

I would start my diagnostics with a fuel pump pressure tester tied into the fuel line so I could watch the fuel pressure while driving the vehicle.