Oxy sensor/s

I would have the vehicle properly scanned. What criteria are you using to determine if it is an Oxygen Sensor problem. These vehicles have several things that can cause them to run poorly and get bad mileage. If you have a bad Oxygen sensor, it would set a code, usually a code 13. A code 12 means all clear and no tach signal until engine is started. ( again normal )

gengeral o2 sensor malf:13,44,45.left bank sensormalf:po131,po132,po133,po134.rigth bank sensor malf:po137,po138,po140,or po141.catalyst o2 malf:po143,po144,po146 or po147.For proper operation of o2 sensor depends on four conditions:Clean eletrical connections with sensors,2.outsde air supply ie:make sure air passages are not retricted to sensors(to the internal part of the sensor)3.proper operating temperature(the PCM will not react until temp reaches appro.600degrees-f 4.unleated fuel must be used for proper operation of sensors.

there is two o2 sensors just took mine off seems to run rich if anyone knows a fix please help

I have a 94,4.3cfi 4wd,mine has one sensor onthe rigth bank.It is hard to see because its on top of the cat.theres a shield that covers the cat which makes it hard to get to,it has four wires coming from it.My engine was doing the same thing so i check the egr valve,because the gase from the engine sometimes producelittle metal pices that can make the pintle in the valve stisk open and allow to much air into the intake,theres a gasket you can buy that has a screen to cover the opening of the air flow that would stop this from happening.I also had no stored codes ,the check engine ligth wasn't communicating with the pcm,so i replaced the pcm myselp cost around $90.00,its not that hard to change.the service engine ligth started working and gave me a code which told me the IAT sensor was bad.sensor cost about $10.00 located in the air tube leading to the plelum on the underside of the hose,i changed it and the car runs fine,hope this gives helps you! good luck

I am having the exact same problem with my 96 GMC 5.7. It will start cold, run perfect for about 10 or 15 min then once it warms up it starts running very bad, Backfires when you give it gas then eventually dies. After letting it set for about 10 to 15 min. It will restart easily. But not until it cools off again. Parts replaced and thrown at it with no sign of improvement: plugs, wires, distributor cap, rotor, cam shaft position sensor, crank shaft position sensor, coil packs, coolent temp sensor. fuel pump, EGR, Ignition control modual. It does not have cats as it is an after market exhaust and cats have been removed. Fuel pressure guage reads 60 psi, What is left?