P0171 Bank 1 Too Lean - Decatted O2 Sensors?

[Kevmobile]

Hey everyone-

A little backstory: my truck is decatted (has the pre-cats still) and has the rear O2 sensors mounted in spark plug defoulers to fool them. I got a lean condition code on the way back from work today, and was wondering if this could be the cause. If I recall correctly, the rear O2 sensors are for emissions, and would not trip this light? I just wanted to double-check and see if anyone has a definite answer as some threads are conflicting.

Also, I am wondering if this is a vacuum leak or not; because I figured if it were a vacuum leak wouldn't both banks be lean?

Thanks in advance for any and all information.

 

[studabaker]

Rich is what I would expect with no cat because it is not burned off. If your truck ran perfect I don't think you would be asking. If you have power loss and a lean code from the o2 sensor this suggests to me your not getting fuel that it is expecting. One benefit of o2 sensor beside emissions. Not really sure how it works or if the mod is part / throwing false code. The o2 sensor sends values back and a high value is rich and a low value is lean. Vacuum leaks are different but similar performance symptoms "roughness". You should be able to hear a bad enough vacuum leak with the hood open and just trace it back. I guess you have some experience with a vacuum leak.