So I put on my 3" downpipe, now after driving for a while it will pop on the SES light saying bank 1 lean (i forget the code exactly). Now the downpipe was used and came with an O2 sensor already in it. Could this be my issue is the O2 sensor is just bad? I know these things are on the edge of still working with the PCM but I just wanted to see if I should replace that or just get an O2 sim.