94 volvo 940

i have a 94 940 and it ran fine and now it cuts off while im driving and then wont start for awhile. i changed the ignition coil and it still did the same thing so i put the old one back on and changed the fuel pressure regulator and it still does it. So i took the wire that runs from the coil to the distibutor off and put it next to the engine block to see if i get a spark and it would sometimes spark and there was times i would get no spark can someone tell what would cause that

Just a guess. Crankshaft position sensor, either the sensor or the wiring to it.