How sensitive are o2 sensors? I'm working on a 5.3 with MP turbo. My long term fuel trim on bank 2 reads good. Bank 1 is reading 25. I found an exhaust leak and fixed it but it hasn't changed the ltft readings. Just bank 1 is running super rich. Plugs are fouling out and I keep changing them to make sure I don't have a dead cylinder causing my problem. I've changed out new intake gaskets with another set of new gaskets. I'm convinced I do not have a vacuum leak. Could a pin hole in the exhaust be causing a false reading at my bank 1 o2 sensor? I'm not seeing any holes but I'm about to pull my crossover pipe off again and check it out. Would anything else cause this issue?

 

Exhaust leaks can throw them off pretty bad. Can you put a wideband in to see if it has the same issue? Maybe it is just the sensor itself.