Code P0171 cause

Hey all. Replaced my coil,plugs,wires,O2 senser pre cat. and air filter as i was having drivability problems.Drove car to work today and on the way home the engine light came on. The code that the scanner showed was P0171 - lean fuel bank 1. Any ideas what would cause this.
 
Thanks  

Only thing I can think of would be the new O2 sensor disagreeing with the old one, on the downstream O2.  Either that or you didn't reset the computer after you installed the sensor.

try your fuel filter? could case a lean condition.. but there are numerous things that could be wrong.. sure you didnt change the wrong 02sensor .. your other conveter could be clogged..usually and 02 sensor will pull a bank1 sensor #  code to tell you the exact one.. just a lean bank could be injectors or many other problems