I have a 96 2wd 5spd f150 with the 4.9l efi. The codes are saying that all the O2 sensors are bad and both banks are lean. I replaced 1 O2 sensor (bank 1 easiest to get to) but the code is still there. I have been having this problem for awhile. After I clear the codes it runs just fine but once I turn it on and off again it starts running lean. Anybody have any suggestions?

 

Maybe attempt to determine if there is a vacuum leak.