Bad Exhaust Mod

[weimgl]

So I've had my 2001 XJ for about two months now and I discovered that the previous owner made a slight modification to the exhaust. As I understand the 01 XJ's have 4 O2 sensors. My XJ only has 3. The guy welded the holes shut and placed an O2 sensor after the "Y". I don't know if he cut the wire to the 4th sensor. If I were to do an exhaust upgrade how would I accommodate for the 4 O2 sensors when my jeep only has 3? I'm a first time Jeep owner and very new to working on cars. But I bought this Jeep to learn so...what should I do? Thanks for the tips!

[finneys98xj]

What header do you have?

[4.3LXJ]

Assuming you have a stock exhaust manifold (header) you should have two before the cat, one on each bank. There should be two more after the cats. If the hole has been welded shut, you can remove the pipe and have a bung welded in. If you are handy, you can drill it and get one from an exhaust shop or Summit Racing and weld it in yourself. Not hard, I have done it twice to my own stuff.

[weimgl]

Assuming you have a stock exhaust manifold (header) you should have two before the cat, one on each bank. There should be two more after the cats. If the hole has been welded shut, you can remove the pipe and have a bung welded in. If you are handy, you can drill it and get one from an exhaust shop or Summit Racing and weld it in yourself. Not hard, I have done it twice to my own stuff.



The guy told me he replaced the old I6 engine with another I6 engine just before I bought it. The odometer read 129500 and I was told the new engine only had 109,000 miles. I took it to a local mechanic (and a trusted friend of the family) and he said the engine swap was a nice clean job.

From what I can tell it is a stock header. Again I don't know much about Jeeps or motors so by header you mean the exhaust that come off the motor? I did read somewhere that there should be two before the cat and two after the cat just as you described. I only have one after the cat and that one is after the "y" merges into one pipe. I've never welded before.

The entire Jeep is stock with exception to the LED interior light upgrade and LED instrument panel upgrade I did about a month ago- and the 20" wheels with high performance tires that came on it when I bought it. I was fortunate enough to snag the stock aluminum alloy wheels when I picked it up and I plan to black them out the wheels and get some new stock tires for the time being.


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[weimgl]

What header do you have?



In believe it is stock. Two before the cat and two after. However, I only have one after and it is installed after the two pipes merge into one.


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[finneys98xj]

Do you have a check engine light on

[bluedragon436]

From what I've found IIRC from a few years back when I was researching this for a friend's 01 XJ we were working on... the 01, only has 3, 1 before each Pre-cat, and 1 after the pre cats before the main cat.. The Comi-fornia emissions version, have the same 3, and then 1 more at the end of the main cat, or after the main cat... I only looked this up because we went to replace all the O2 sensors on it, and only found 3, and the auto part store also showed 3, and I was confused because my GF's 06 LJ, has 4, and I now most modern cars have 4.. so wasn't sure on the 3, seemed very odd to me..

[weimgl]

Do you have a check engine light on



Yes. Light is on an code is P0138 code.


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[weimgl]

From what I've found IIRC from a few years back when I was researching this for a friend's 01 XJ we were working on... the 01, only has 3, 1 before each Pre-cat, and 1 after the pre cats before the main cat.. The Comi-fornia emissions version, have the same 3, and then 1 more at the end of the main cat, or after the main cat... I only looked this up because we went to replace all the O2 sensors on it, and only found 3, and the auto part store also showed 3, and I was confused because my GF's 06 LJ, has 4, and I now most modern cars have 4.. so wasn't sure on the 3, seemed very odd to me..



That's the first I've heard of 3 O2's on a stock. I've looked at other 01 Cherokee's and have seen all 4 O2 sensors. Looking at mine I assumed it has been modified. The check engine light is on and it's giving me code P0138.


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[bluedragon436]

That's the first I've heard of 3 O2's on a stock. I've looked at other 01 Cherokee's and have seen all 4 O2 sensors. Looking at mine I assumed it has been modified. The check engine light is on and it's giving me code P0138.


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Yeah, like I said, I'd never heard of 3 on a stock setup until I saw it on his.. and looked online.. Seemed to be about 50/50 as far as folks having either 3 or 4 on their 01 XJ's... After working on his I've seen a few other 01's that have had 3, and I've seen at least 1 if not 2 that had 4... so I don't know what the deal is with that one... He had code as well for downstream O2, and we replaced them all and code went away.. so not sure if replacing the lower one would remove your code... or if like you said he cut wires and it's going to go crazy until you find them and reconnect.. Have you had that code since you got the XJ??

[weimgl]

Yeah, like I said, I'd never heard of 3 on a stock setup until I saw it on his.. and looked online.. Seemed to be about 50/50 as far as folks having either 3 or 4 on their 01 XJ's... After working on his I've seen a few other 01's that have had 3, and I've seen at least 1 if not 2 that had 4... so I don't know what the deal is with that one... He had code as well for downstream O2, and we replaced them all and code went away.. so not sure if replacing the lower one would remove your code... or if like you said he cut wires and it's going to go crazy until you find them and reconnect.. Have you had that code since you got the XJ??



Yes I've had the code since I got the Jeep. I have not replaced the three sensors. What brand do you recommend? I also notice a very strong omissions smell from the exhaust. Much more noticeable than other vehicles. Is this normal? What would cause a strong emissions smell like that?


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[Mudderoy]

https://img.vehiclepad.com/8ee6f89965f614874e632ae0c424f50a_cherokee-o2-sensor-advice-jeep-cherokee-forum-1999-jeep-cherokee-xj-o2-sensor-diagram_1024-887.jpeg

[weimgl]

https://img.vehiclepad.com/8ee6f89965f614874e632ae0c424f50a_cherokee-o2-sensor-advice-jeep-cherokee-forum-1999-jeep-cherokee-xj-o2-sensor-diagram_1024-887.jpeg



Thanks for the pic. My exhaust is missing the two down stream O2's and has one on the part of the exhaust that is not shown in the picture. Have any idea what O2 I should use there?


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[Mudderoy]

Thanks for the pic. My exhaust is missing the two down stream O2's and has one on the part of the exhaust that is not shown in the picture. Have any idea what O2 I should use there?


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If you have the 2001 ECU you need to have 4 O2 sensors (well according to this picture). I've never popped the hood on a 2000-2001 XJ. If you have say a 1999 ECU then you'd need 2 O2 sensors.