I was driving to work this morning when van died at a stop light.  Tried starting her again with no luck.  Turns over fine but won't fire up.  Could this be an O2 sensor problem or possible fuel filter?  When trying to start her she is trying really hard to start, very strong turn over....  I'm sure I'll walk to her later and she'll fire right up for me but I'd like to solve this problem.  Thanks for any help.

 

Bob