i have a problem with my wifes truck. the o2 senser set off the check engin lite. 2 times. over a month ago. truck runs fine. lost over one hundred miles. she wouldget around 150from full to 3.4 tank. now shegets 100 if that from full to half. no one is stealling gas. (locking cap)tire are all up , new air filter ,fuel filternew plugs,wires,cap. (plugs gaped a60) this was all done when she was getting 150. question is would that senser still be screwing it up and costing her big in gas?

 

Sounds like a bad fuel pressure regulator..