97 silverado 2500 hd 02 sensor problem

Truck ran perfect until one day under a load started sputtering and backfiring. I hooked up to a computer and got a reading for EGR valve and both pre converter 02 sensors. After replacing plugs,wires,rotor cap and button, EGR vavle, and both oxygen sesnors I reset the computer. It drove fine for about 30 miles then the check engine light came back on and the old problem came back. After checking the computer again it showed P0151 02 sensor which I have just replaced. It feels like a timing problem to me but what would cause the 02 to go bad or read bad and what else could possiby be my problem? 5.7 vortec

Truck ran perfect until one day under a load started sputtering and backfiring. I hooked up to a computer and got a reading for EGR valve and both pre converter 02 sensors. After replacing plugs,wires,rotor cap and button, EGR vavle, and both oxygen sesnors I reset the computer. It drove fine for about 30 miles then the check engine light came back on and the old problem came back. After checking the computer again it showed P0151 02 sensor which I have just replaced. It feels like a timing problem to me but what would cause the 02 to go bad or read bad and what else could possiby be my problem? 5.7 vortec

Check engine tune up and fuel pressure for up to specs first then.
Did you use a oem type o2 sensor. All fuses good?
1) Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. - BASIC TESTING - 5.7L . After performing OBD system check, go to next step.
2) Install scan tool. Warm engine to normal operating
temperature. Place gear selector in Park or Neutral. Apply parking
brake. Increase engine speed to 1200 RPM. Monitor H02S voltage using scan tool. If H02S voltage is less than .086 volt, go to next step. If H02S voltage is not less than .086 volt, go to step 4).
3) Turn ignition off. Disconnect H02S connector. Connect a
jumper wire between H02S ground circuit of H02S connector (VCM side) and ground. Turn ignition on, with engine off. Monitor H02S voltage using scan tool. If H02S voltage is .35-.55 volt, go to step 7). If H02S voltage is not .35-.55 volt, go to step 5).
4) DTC is intermittent. If no additional DTCs are set, see
DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
5) Check for short to ground in HO2S signal circuit. If a
problem is found, go to next step. If a problem is not found, go to step 8).
6) Repair circuit as necessary. After repairs, go to step 9). 7) See DIAGNOSTIC AIDS.
8) Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
9) Using scan tool, select DTC, CLEAR INFO. Start and warm
engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0151. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and

passed, repeat step 2).
10) Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

Diagnostic Aids
Using scan tool, observe Long Term (L T) fuel trim values at different RPM and air flow conditions. Scan tool should display fuel trim cells so that L T fuel trim values can be check in each cell to determine when DTC may have set. If DTC is set, L T fuel trim values will be about 158 or greater.
Check for mispositioned HO2S wire pigtail contacting exhaust manifold. Check for intermittent ground in wire between connector and sensor. Check for poor VCM to engine block ground. Check for lean fuel injectors. Check for water near in-tank fuel pump inlet that may be delivered to injectors. Water causes a lean exhaust and can cause DTC to set.

System will be lean if fuel pressure is too low. Monitor fuel pressure while driving vehicle at various speeds and loads to verify pressure. Check for an exhaust leak that can cause outside air to be pulled into exhaust and past sensor. Check for vacuum or crankcase leaks that can cause a lean condition and possibly high idle. If all above checks are okay, H02S is faulty. DO NOT solder H02S wires.

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