I am a new jeep owner. Just bought a 1990 jeep and have so far been towed twice and then off to a muffler shop. All is suppose to be perfect on it now except i am noticing i am inhaling lots of exhaust. Didn't seem to do that before. Muffler guy said he fixed holes and added a new muffler and that i am just picking up exhaust from it running with the top down. It has no ac so i plan on always having the top down. I googled and asked him about the o2 sensor? Maybe it went bad and i need to replace it. He says if so the check engine light would come on and i would hear it making noise. The more i google the more i am finding there is no check engine light on the 1990s. How hard is this job and can i change it myself? I like having a machanic that will help me keep this thing running but i am kinda interested in doing pthings if capable. Any suggestions on part to use? Looks like the one on there is a single wire with no heat? I will post some pics.... any help and advice is appreciated. Thanks