Hey I got 04 g35x with test pipes untuned all summer long I didn't have any codes or any issues but it started getting cold now iam starting to get an 1273 code bank 1 lean I've been checking everything and everything testing good only werid thing is I can watch my af 1 sensors and bank one is at 110 percent to 114 but bank 2 is 104 to 105 is that normal cause I don't have a tune or is something wrong since they aren't even I've checked intake and exhaust leaks I have none and I have nothing wrong with fuel or spark

 

Test pipes don't normally cause upstream O2 sensor issues, I'd see what actual conditions you have in the chamber, compare to bank 2 and they should be close to the same color. Chances are you have a plug issue, a fuel delivery issue, or an intake leak. Be sure to check all the PCV hoses.

What's your LTFT on both banks?

 

Well I had this issue before I fixed it by replacing the valve covers I've replaced the af 1 sensor and triple checked intake and exhaust leaks no leaks I've replaced fuel rail and the injectors

 

Have you actually smoke tested the intake and exhaust for leaks?

 

Yes I have 3 times I have no reason why it would be like this and what's weird is I haven't had code all summer but first time it got cold I got the code but now it's cold and sometimes I drive it 7 trips without code sometimes I just can't get it to clear and it keeps coming back