Delete the cats or not?

Chris said:
I thought you’d never ask 😉



On the last one I deleted the third cat, on my current one I am deleting all three cats. Once removed I just use HPTuners to disable the post cat O2 sensors which will make it so it runs great and no CEL or error codes are triggered. I am also installing full long tube headers at the same time.

It’s very easy to remove all the cats, but if you live in a place with emissions or inspections, you won’t pass. We don’t have that here.

I also love the way they smell without cats. Reminds me of my 69 Camaro.

I should also point out that while this is technically illegal, I don’t care what you do or what you don’t do with your Jeep, it is your Jeep after all. Just make sure that you’re aware that you won’t pass emissions or inspections if your state has it.

The 00-06 models are particularly restricted with THREE cats whereas the earlier models only had one.
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Gotcha. Yeah here they do emissions tests and visual inspections so even if there is no CEL I'd fail.

The 3rd cat fell apart inside on a friend's 2001 XJ, so I gutted it but left it on, that way under visual inspection the can was still in place.
 
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jeepguy03 said:
Gotcha. Yeah here they do emissions tests and visual inspections so even if there is no CEL I'd fail.

The 3rd cat fell apart inside on a friend's 2001 XJ, so I gutted it but left it on, that way under visual inspection the can was still in place.
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The third cat isn’t the big deal, it’s those two big cats in the down pipes that always seem to fall apart or have issues. They are also restrictive as well. I might even be inclined to keep the third cat as a means of noise reduction.
 
So you have a tuner that can throw off the CEL coming from the second 02...???

I'm not in the tuner industry but there seems to be a lot of mfg of tuners that can override a CEL caused by the second 02.....no?

What i don't understand here is in your link you said about leaving the last cat in place to help with noise but going to remove the last 02?
Do you know what the last 02 actually does?
 
jeepguy03 said:
If you remove the cat on a '98 you will (should) get a check engine light, since there is a O2 sensor downstream from the cat. I know on my 98 there is.
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Yet no code. It ran like that for a few months until I could get a new cat in place. No software or tune at the time.
 
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Chris said:
The third cat isn’t the big deal, it’s those two big cats in the down pipes that always seem to fall apart or have issues. They are also restrictive as well. I might even be inclined to keep the third cat as a means of noise reduction.
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Yeah the only reason my friend's 3rd cat fell apart on his '01was too many encounters with rocks. 😆
 
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Rubicon88 said:
So you have a tuner that can throw off the CEL coming from the second 02...???

I'm not in the tuner industry but there seems to be a lot of mfg of tuners that can override a CEL caused by the second 02.....no?

What i don't understand here is in your link you said about leaving the last cat in place to help with noise but going to remove the last 02?
Do you know what the last 02 actually does?
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There are two manifold cats, each have an O2 sensor before and after them for each bank of the manifold. The 3rd cat is further downstream near the muffler and doesn't have any sensors near it. I think Chris means he will delete the O2 sensors around the manifold cats when he removes them, and leave the 3rd cat downstream that has no sensors around it.


Omix_Ada_Pipe_Converter_TJ_17613.27.jpg
 
jeepguy03 said:
There are two manifold cats, each have an O2 sensor before and after them for each bank of the manifold. The 3rd cat is further downstream near the muffler and doesn't have any sensors near it. I think Chris means he will delete the O2 sensors around the manifold cats when he removes them, and leave the 3rd cat downstream that has no sensors around it.


View attachment 195217
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Ok....

So then how is he going to achieve the goal of 14.7:1 AFR?

The upstream O2('s) are there for 1 purpose. To try an always achieve the perfect air fuel ratio. That's it. Nothing else.

The downstream O2 only purpose is to notify if the rear Cat is failing. Thats it. It has absolutely no impact on engine performance. Zero.

The upstream O2's are paramount for the attempt of achieving the perfect air fuel ratio. They are adjusting all the time in warp speed to maintain optimum AFR.

I'm curious how this is achieved by a tune that is getting zero real time feedback from the exhaust to determine the proper AFR if removing the O2"s...???
 
The reason I asked was in case it caused any problems on a TJ, this is a common practice on some Jeeps in Australia, my brother recently had it done to his 2010 Rubicon when fitting a new exhaust.
I have ordered 4 new 02,s for my 06 anyway.
 
Rubicon88 said:
Ok....

So then how is he going to achieve the goal of 14.7:1 AFR?

The upstream O2('s) are there for 1 purpose. To try an always achieve the perfect air fuel ratio. That's it. Nothing else.

The downstream O2 only purpose is to notify if the rear Cat is failing. Thats it. It has absolutely no impact on engine performance. Zero.

The upstream O2's are paramount for the attempt of achieving the perfect air fuel ratio. They are adjusting all the time in warp speed to maintain optimum AFR.

I'm curious how this is achieved by a tune that is getting zero real time feedback from the exhaust to determine the proper AFR if removing the O2"s...???
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A wideband O2 sensor and a custom tune.

And I'm sure you already know this, but the 14.7 perfect air fuel ratio is only "perfect" at certain throttle positions like idle and very light throttle input. Also, the narrow band basically sees rich or lean of 14.7. It works like an on/off switch.
 
Skylinessuck said:
A wideband O2 sensor and a custom tune.

And I'm sure you already know this, but the 14.7 perfect air fuel ratio is only "perfect" at certain throttle positions like idle and very light throttle input. Also, the narrow band basically sees rich or lean of 14.7. It works like an on/off switch.
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But you just said he was removing the O2"s....around the manifold. Meaning the upstream O2's. Then you say he will be using an O2.

The 14.7:1 ratio is the perfect AFR...that is never achieved in reality. But it's constantly trying to get there in real time all the time.
 
Rubicon88 said:
The 14.7:1 ratio is the perfect AFR...that is never achieved in reality. But it's constantly trying to get there in real time all the time.
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Incorrect.

And a wide band O2 sensor would be independent of your factory PCM. It's something you would look at to tune or datalog and tune.
 
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Skylinessuck said:
Incorrect.

And a wide band O2 sensor would be independent of your factory PCM. It's something you would look at to tune or datalog and tune.
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Excuse me?

What's incorrect?

The perfect air fuel ratio is never just sitting at 14.7:1...
The moment the throttle changes the ratio changes. Once an engine warms at idle it's constantly changing based on the feedback from the O2 in the exhaust giving information to the computer. The components are constantly working to achieve the perfect AFR in lightning speed.

You said he was removing his O2 sensors..the upstream O2's but didn't say he was replacing them with another O2 until posts later.
 
14.7 is stoichiometric. That is the best air/fuel ratio for the most complete and efficient burn (for gasoline). It is not the "perfect" a/f ratio under several conditions that your motor sees all the time like decel, wide open throttle, etc. Your vehicles computer is not always trying to get to that a/f ratio. It's only trying to get there under certain perameters commonly known as "closed loop." 14.7 would waste gas on decel. 14.7 would be way too lean at wide open throttle and make much less power at best, or hurt the motor at worst.

You asked how he would get to 14.7 (which he only wants to do some times) without the factory upstream O2 sensor. I told you. He used a wide band O2 to see what was what and tune his pcm accordingly.

If you would like me to go over the pros and cons of a custom tune not utilizing the factory narrow band o2 sensor just ask. And BTW, since a narrow band only measures richer or leaner than 14.7, it can't be used to do major tuning, especially at WOT.
 
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Skylinessuck said:
14.7 is stoichiometric. That is the best air/fuel ratio for the most complete and efficient burn (for gasoline). It is not the "perfect" a/f ratio under several conditions that your motor sees all the time like decel, wide open throttle, etc. Your vehicles computer is not always trying to get to that a/f ratio. It's only trying to get there under certain perameters commonly known as "closed loop." 14.7 would waste gas on decel. 14.7 would be way too lean at wide open throttle and make much less power at best, or hurt the motor at worst.

You asked how he would get to 14.7 (which he only wants to do some times) without the factory upstream O2 sensor. I told you. He used a wide band O2 to see what was what and tune his pcm accordingly.

If you would like me to go over the pros and cons of a custom tune not utilizing the factory narrow band o2 sensor just ask. And BTW, since a narrow band only measures richer or leaner than 14.7, it can't be used to do major tuning, especially at WOT.
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LOL...

That's rich.

So on one hand you say its the perfect ratio...but then say it's not the best.

In every single one of your scenarios the optimum air fuel ratio is what? 14.7:1
We can have less parts air and fuel or more parts air and fuel to achieve that ratio but that is the best ratio

You want to nit pick and play with the ratio on a 4.0? L O L...
You going to find another 6 horsepower? Well hold the phone and stop the presses...we'll definitely feel that difference.
We're not talking a race engine here.

It's just a Jeep engine chugging along doing it's thing. It isn't much of a thing but it's a good thing.
 
Even though I feel like I should be grumpy, I'm not, so don't take this the wrong way. You don't understand what you are talking about if you think an engine should always be trying run at 14.7. Maybe I'm just not understand what your are saying.
 
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Rubicon88 said:
LOL...

That's rich.

So on one hand you say its the perfect ratio...but then say it's not the best.

In every single one of your scenarios the optimum air fuel ratio is what? 14.7:1
We can have less parts air and fuel or more parts air and fuel to achieve that ratio but that is the best ratio

You want to nit pick and play with the ratio on a 4.0? L O L...
You going to find another 6 horsepower? Well hold the phone and stop the presses...we'll definitely feel that difference.
We're not talking a race engine here.

It's just a Jeep engine chugging along doing it's thing. It isn't much of a thing but it's a good thing.
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I just reread that. You don't understand what I explained or what you are talking about. Spend some time googling and learn.
 
Skylinessuck said:
I just reread that. You don't understand what I explained or what you are talking about. Spend some time googling and learn.
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I completely understand...and no matter how many times you want to copy and paste something it still doesn't change the fact of 14.7:1 is the optimum AFR for these engines.
You want to run at WOT? Then lower the ratio to work better at WOT... but it's still a 4.0......in a Jeep.
Perhaps you are entering it in the open class at the Baja 1000. You're still about 4-500 horsepower shy of what you need.
Perhaps it's a new mud buggy and need big horsepower to do some mud bog competitions.

Again it's still several hundred hp shy of what that needs and won't achieve that with any magical tune nor rich AFR on a 4.0 ..... because.... it's still just a 4.0
 
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