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Originally Posted by SamtheKorean
Ah that makes sense, I know knocking in engine can cause by improper air to fuel ratio, do you think having a faulty upstream and downstream o2 sensor can cause this problem?
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Yes, it is definitely possible. The more upstream sensor is the important one for afr as I recall. The one further downstream is just a check to make sure the cat is working , which I think you don't have. Running lean is likely to induce knock.
Any idea what your ltft is? It changes at different load values (load increases with airflow) so you might need a log to see it. Basically if your o2 sensor is messed up, you are likely to see large + or - values in your fuel trim.