putterd 2 a stop

My '02 Ram 1500 Conversion van with 55K miles puttered to a stop and will just turn over and not start. You can hear the pump humm when the key is turned on. So i think the pump is okay. It will start with starting fluid. i haven't yet checked the fuel pressure. any other idas as to what might be wrong? gotta fix this one quick. it's my wifes van and when she's not happy... need i say more!

Okay, I've read the codes and i'm getting codes P-0138 (HO2S Circuit High Voltage Bank 1, Sensor 2), P-0171 (Fuel Trim System Lean Bank 1) and
P-0308 (Cylinder 8 Misfire Detected). Any Suggestions???

Crank position sensor? My 97 3.9 died on me on vacation 1100 miles from home in 99 and it ran out of warranty on the way to VA from KS. The part was $40. The CPS is under the distributor cap. It is the black round thing that lays under the cap. It controls the injector timing. Also, check for spark. The crank sensor contorls the spark and it is bolted down on the bell housing behind the passenge side cyl head and is held on by 2 allen head bolts.