Bad oxygen sensor

[fred]

Boy was complaining about bad gas mileage on his truck. He has a Ford F150 1997 4.6l.with 4 sp auto. I ran some fuel trim tests and they were high. Bank 1 long term +12 and bank 2 long term +15. I then ran an oxygen sensor test. Oxygen sensor on BANk 1 sensor 1 looked ok however oxygen sensor 2 had zero volts and graph was empty. So i believe that one is bad. bank 2 sensor one also looked good however bank 2 the sensor had one spike on the graph so I believe that sensor is also bad. Am I correct in this assumption because the computer has not thrown any codes. Truck runs good and idles smooth also not blowing any black smoke. But he is only getting 9 miles to the gallon.

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[fred]

Turns out Bank 1 sensor 2 was bad. Bank 2 sensor 2 is good. So I only had one sensor to replace. I just bought a new diag tester with graphing capability which really helped figure it out.

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