Toyota Repair: 99 toyota code P0171, oxygen sensor, fuel rails

Question
First thank you for your help on the interference/non-interference on my father in laws truck. He has been getting a P0171 code from an OBD11 reader, after having his check engine light come on. It states also that fuel too lean bank one. He changed the fuel filter,and the air filter as well, but it still faults to this code. Is there filters on the fuel rails, or what could you suggest. Thanks again.  

Answer
No there are no filters on the rails. It could be your fuel injector is beginning to plug so it is not sending enough fuel into the intake manifold. If he has any codes for an oxygen sensor this could be sending a messge to the ECM that the exhaust is too rich and is causing the system to lean out on the fuel delivery. My honest thought is that if the vehicle has more than 100k for mileage, you may want to service your injectors. You can have them serviced at most repair facilities, or if you feel comfortable doing them yourself, you can save a lot of labor charge and just replace the injector on the one bank. Before you perform any of these tasks however, make sure all connections to this cylinder/bank are fully connected and no prongs on the connections are bent.