Today my 1990 nissan terrano/pathfinder just stopped running. wouldnt start back up but would turn over fine........

Sudden death in vehicle is usually based on something electrical. Check fuses and relays with fuses. Check 1) spark on each plug in turn 2) crank sensor 3) coil 4) cam sensor 5) main relay. Put ignition on position 2 and listen at the open fuel filler pipe for the pre-pump operating. Listen for main pump operation. (If unsure what it is you are listening for remove the fuse for the pump and you nshould notice it being quieter) Check fuel rail for pressure (there is a Schrader 'tire' valve on the fuel rail for pressure testing purposes). If fuel flow is low then this could be blocked fuel filter or tired pump. Finally make sure throttle body is good and clean internally at least and that associated idle air valve is clean and working. With fuel air and spark at the right moment the engine should run. My gut feeling is the crank sensor