Alright guys so ive been getting Code 21(Oxygen sensor or circuit. O2 sensor or wiring faulty) on my 1994 for a while now. It was coming on basically every time i would drive even the 5 mile trip home after school. Normally in the morning i can go code free but i seemingly always get one on the way home after its been outside in the heat. Any way, i replace the O2 sensor a week ago yesterday. Brand new NTK from RockAuto. Didnt get a code on the 10 mile trip home from my grandpa's where we changed it. So i guess im at the conclusion a wire is geeked up or another sensor is causing it to run this way. I feel like i can smell gas when i cut the Jeep off or some times when i stop so i guess its running rich but im out of ideas. Any body got suggestions or dealt with this before?

 

Any leaks in your exhaust manifold?

 

I agree with this. Only because you mention that you can smell gas when you shut it off. And if your exhaust manifold has a crack in it, it'll throw your o2 sensor off

 

Not that i can clearly tell. The only sound i hear when its idling is a rocker arm tapping but i mean its nothing that make the jeep run rough. The engine doesnt get louder at higher rpms either. Whats the best way to tell if i cant see a definitive crack?

 

A visual inspection. Sometimes it's easy to hear but other times (in my case as well), you can't really hear the noise. I'd shove a mirror down there and take a look around with a flashlight at every inch of the manifold, front and back of it

 

crack in the manifold is the most likely cause of a rich condition. the extra oxygen in the stream is reading as a lean condition throwing off the 02. once the fuel trim shifts far enough the computer will throw a code. you can always try resetting the battery and see if it changes anything.

the dorman OE replacement manifolds are about $100 shipped and the walker front section is $45 shipped if you decide to do both.

 

Have someone temporarily plug the tailpipe while you listen for escaping exhaust.

 

^ that would work too

 

Alright ill do that test soon. Lets say i have to replace it, what all do i need? Is the front section your talking about from the header to the cat?

 

Anything before (engine side) or around the first o2 sensor could do it. After the sensor (muffler, etc) isn't as important, sensor can't see what's already blown past.

 

Alright i took it to a muffler shop and they found a crack in it . I talked to my grandpa and it looks like well fix it sometime this summer, so it'll eventually get done. Its a crack about the width of a pube on the section where the two pipes on the manifold make one. Whenever we fix it were gonna pull the whole thing out and let me try out my welding skills

 

New parts will be a more permanent fix than a weld and are really not that expensive. Under $100. I'd recommend going that route.

If you weld it, it is VERY likely to crack again.

 

Yeah i agree and this is a contradiction to that but if the exhaust shop does that then ill do it. Even if they do that just so you bring the vehicle back up to then ill give it a try. Yeah its rickety but it'll buff out

 

I have the same problem. Would that also lend to the jeep havin a rough idle or when the CEL is on (on occasion in mine) have a higher idle (1k rpms). I replaced only the front o2 sensor. Was fine for four days (Ntk sensor) now cel back on

 

Mine does the same. Ive had the high idle for about a year now (before the crack happened i think). I think my crack was a result of a bad motor mount that one day decided to separate and it gave the motor a LOT of flex for the week or so until i replaced it. Idk what the high idle would be caused by but it doesnt bother me since it tends to go away. Ive noticed rough idle but its very rare, more like a misfire than it is a rough idle though for me.