1998 4.3 4 door 4x4 with 103K miles. First off im not having any issues except not the best of fuel millage. I read that the O2 should be changed at 100K. Besides cap, rotor and plugs and wires should I change the O2 sensors or leave well enough alone. Thanks

 

Up to you really, I go with the,,, if it ain't broke don't fix it. But I have heard it can help mileage

 

The PCM relies heavily on oxygen sensor data for fuel management, which directly affects fuel mileage. The sensors react to changes both rich to lean, and lean to rich. The faster it responds, (in both directions) the better the fuel mileage will be. Oxygen sensor reaction time slows down with miles: by the time you reach ~100k miles, the reaction time has slowed enough that it will noticeably affect fuel mileage. That's why it is recommended to replace them. AC Delco and Denso sensors have the fastest reaction times, and they will provide the best fuel mileage.

 

Yes Denso O2s.