s i went to replace my O2 sensors today and i need to replace my front one and the guy said i had one front one and one back one but when i went to replace it there were two front ones or was i not looking in the right spot because they both looked the same as the new one i had sitting in my hand

 

yeah you have two front ones.did this earlier this year. the only way to tell which one needs chencging is pull one and swap it and see if your light is still on

 

My '01 4.0L has two on each bank on the Y-pipe, and another in between the last two cats. Total of 4 cats, and 3 O2 sensors.

Do you have any codes getting thrown? Check engine light? P0175 is bank 2(pss side) and P0174(driver side) rich codes. I'm thowing 175 right now.

 

The code will tell you which side is bad. Bank 1 is the passenger's side, Bank 2 is the driver's side.

 

opposite of chevy? ok..i just finally learned that i guess. lol.

 

what might be a possible cause if you are getting a code for both banks 1 and 2 at once?

 

A Vacuum leak.
I know the OHV 4L (like mine) would develop a vacuum leak due to a failed upper intake manifold gaskets. I also had to replace the gasket beneath the fuel rail.
But you have a SOHC judging by your avatar.

I would still suspect you have a vacuum leak if your getting a lean code for both banks at the same time.

 

OHV 4Liters are know for getting vacuum leaks and it could be b/c the upper intake manifold gasket is bad??? Dang that sucks, i have a vacuum leak, could be what it is. Still havent had the smoke check done yet

 

I hopefully found my vacume leak last night. The rubber elbow that connects the plastic tube from the PCV to the plenum had a hole in it and the rubber seems really weak. Gonna get one today and hope its all that I have wrong.