If if your O2 sensor gets fouled with oil on it it will create improper or incorrect readings even though it is reporting it could be reporting the wrong scales and then your truck will start to adjust certain things to keep your combustion where it wants it my suggestion is to take a look at your pre and post O2 sensors and see if either one of them are fouled with oil on the outside part O2 sensors are two part sensors with detections on inside the pipe and outside the pipe on the same one sensor that way it compares the outside atmosphere to the in the pipe atmosphere reading for hydrocarbons but if it gets oil on the outside sensor your hydrocarbons are going to read exactly what's going on in your tailpipe and it's going to make some drastic adjustments to try to get your truck running right when it's running fine sort of a false false information being sent to the PLC and the PSL tries to correct it getting based on with the sensor to tell him if the sensors got oil on it replace it and then fix the leak