It’s helpful that you’re using an OBD2 scanner to read fault codes, allowing for targeted troubleshooting before replacing parts unnecessarily. When analyzing fuel trims, the total fuel trim for each bank is crucial. In your initial readings, Bank 1 shows a total fuel trim of approximately +23%, while Bank 2 is around +8%. A +23% reading is significantly high and indicates that the engine’s computer is adding a substantial amount of fuel to compensate for a lean mixture.
This situation presents a classic cause-and-effect dilemma: misfires can cause the exhaust oxygen sensor to read lean, but a genuinely lean air-fuel ratio can also trigger misfires. Since you’ve already ruled out many other misfire causes, a lean air-fuel ratio appears to be the primary suspect.
However, before concluding that the issue is Vortec injection poppet related, it’s essential to examine the output voltages from all four exhaust gas oxygen sensors. With the engine fully warmed up and at idle speed, monitor the voltage output from the upstream sensors (Bank 1 Sensor 1 – B1S1 and Bank 2 Sensor 1 – B2S1). Under normal operation, the voltage from both upstream sensors should fluctuate continuously between roughly 0.1 volts and 0.8 volts. Using an app that graphs these readings is the most effective way to assess oxygen sensor activity.
If, after the engine is warm, the voltage from any oxygen sensor remains constant at around 0.5 volts, it suggests a problem with the sensor itself or its heater circuit. To further investigate, try holding the engine speed steady between 2,500 to 3,000 RPM and observe if there’s any change in sensor activity.
If the output from either the B1S1 or B2S1 sensor is fixed at a low voltage (below 0.5V), try quickly fluttering the throttle – very small, rapid taps. This action should momentarily enrich the fuel mixture and, if the sensor is responsive, drive the voltage reading upwards towards 0.9V.
As an additional diagnostic step, you could try disconnecting the Mass Air Flow (MAF) sensor to see if there’s any improvement in the readings. However, based on the initial symptoms, a MAF sensor issue seems less likely in this case. It’s also worth noting that the condition of the OEM air filter and intake air tubes is critical, especially for MAF-based engine management systems, as restrictions in airflow can significantly disrupt fueling.
