Hey all,

Had a quick question regarding exhaust systems on later model Xj's (mine being a '99 4.0L)
It was explained to me that because my year - as with later years - has two 02 censors, a highflow cat would produce two different readings and therefore result in the signal for less fuel delivery from the computer.
Is this accurate? I'm just wondering if replacing my current cat with a nother normal one will negate any performance or benefits when I do an aftermarket exhaust? IE Flowmaster, header, etc. Is there any way to skirt around this problem with that second censor and still be okay when my vehicle has to pass air emissions tests?

Any and all help is appreciated,
Happy wheeling this weekend.

 

im not sure of exactly what you are saying but i think all xjs or at least around 90 and up have 2 sensors, 1st on header/downpipe then second on cat/behind cat. If you go with a magnaflow cat then the sensor bung is already welded in place and ready for you. This is what most people run. I got mine off ebay for $90 shipped with the OBO thing. I hope this helps, if not let us know lol.

 

No, whoever told you that is completely wrong.

The 2nd o2 sensor is just for the computer to know if your cat is working or not. You can buy simulators to get rid of the 2nd o2 sensor alltogehter, but in some states that may be illegal, and for off road use only. Up to you to do the research there.

If you put a high flow cat on the truck, it may trip a CEL, because the cat is letting more flow happen. If that is the case, you may have to get a sim. That depends on your truck and how sensative the PCM is.

 

That makes sense. I'm not gona lose the benefits of an aftermarket exhaust system with a regular cat on there will I?

Thanks for the info btw.

 

Why would a hi-flo cat trip a CEL?.......neither of the O2's is measuring any kind of flow.

 

The cat will be the "bottle neck" in the system. If there is any restriction that'll be it. So, in a sense, yes, it will hinder the flow a bit, but I'm not exactly sure how much.

It would trip a CEL if the rear o2 is sensative enough to pick up the higher flow of gasses, and reduced burning capacity.

Hey, I'm not a Jeep expert, an o2 sensor expert, or a cat expert. I have just seen cars that trip CEL's with a high flow cat. Don't know why, I just assumed it was because of the ECU not knowing WTF to do with the rear o2 reading after the cat being swapped.

Like I said, it may. I didn't guarantee it would, but I also didn't wanna leave out any of my knowledge that could help the OP understand whats happening. I didn't wanna seem like a d bag for not saying anything about that end of things. I like covering all bases when possible.

 

missread and couldnt figure how to delete this post. sorry lol

 

Yep, my apologies, I could have posted what I did better/differently.

 

Meh, its the internet. You can't really pick up inflection, so its hard to tell what attitude people have.

I wasn't worried about it, and you were right, I was a touch unclear with my first statement about the CELs popping.

 

Technically, as long as the upstream O2 is in place and functioning correctly, the downstream O2 just needs to be connected to the wiring harness (and functioning correctly), and nothing else. No CEL.

 

So in your opinion I could run a high flow cat with no problems?

 

Yes, I think that is the conclusion you could draw from what everyone has said.

 

I'm just saying as long as both O2s are connected and functioning properly, a CEL shouldn't be triggered. There's 2 reasons why an O2 triggers a CEL, it's voltage falls out of design parameters and/or it's heating element fails.

 

Most CAT's now are high flow. You can pick up a universal cat from (I think) performance-curve.com for around 40$

 

I helped my buddy put a High flow cat and flowmaster on his 99 and he has had no CEL's of anykind related to the exhaust....he also has a header. So u shouldnt have any problems.