Hi guys, I have a 2003 350z that is running lean on both banks and I cant figure out how to fix it. I have swapped out all O2 sensors upstream and downstream multiple times (I have a friend that works at autozone and let's me borrow parts) i have put in all new injectors. New coils. New Spark Plugs. New fuel pump. Took it to shop and had the car smoke tested for vacuum leaks. None. Pcv valve replaced. Cleaned 1st MAF sensor and eventually replaced it. The engine is completely stock. Which leaves me with the exhaust system. I dont know much about cars, but is there any mods that can be done to the exhaust system that can cause my vehicle to run lean? Muffler delete? Resonator delete? Maybe both? The car belonged to my brother who recently passed. And The only performance mod on the car that I know about is the exhaust. This thing is loud. The codes the car is throwing are P0171 and P0174. Car running lean bank 1 and bank 2. Any help would be greatly appreciated! Thanks Guys!

 

I think they make sensors specifically for aftermarket exhausts for this reason. I'm just guessing. But if the cats were deleted and all, and you're running OEM sensors that are made to read gases with cats installed, may wanna do some searching
https://itstillruns.com/bypass-oxygen-sensors-5409829.html

 

Thanks brother, i will look into it!