Remove catalytic converter?

[88Sahara]

Hello Folks. New member, first post. I didn't see anything come up on this topic so I'll ask and hope this hasn't been hashed to death.
I have an '88 YJ with the carburated straight 6 engine. Computer died just after I got it so I bypassed it. Jeeps runs ok, some idle issues and a little acceleration hesitancy, and some exhaust noise and leaking. Still fun as all get out for jeeping around the county. Historic tags, no inspections or emissions testing required.

My questions is can I/should I remove the catalytic converter and run straight pipe to the muffler? At 115k miles I think the converter may have some restriction, and I have no sensors to worry about. My thought is this will reduce back pressure, help the engine breath better and with tight pipe connections/good muffler should eliminate exhaust leaks and hopefully excessive noise.

Will the removal hurt my engine or its performance? The forums seem to be filled with contradicting opinions. Most of the negatives seem to apply to newer, more complicated engine systems (makes perfect sense). Most of the positives seem to apply to the off-road guys. I don't do much off-roading but I do like to enjoy the Jeep on nice days and local road trips. It has to at least sound legit.

As to the how part I will probably remove the flange bolts and either buy or build a 'test tube' that will bolt in (so it can be easily reversed).

Thanks in advance to any who may offer advice.

 

[Gilaguy23]

My $.02 worth. Generally speaking vehicles that run a 02 sensor after the cat are affected in a bad way when the cat(s) are removed. Thats not you though. Ive had 3 vehicles that the cat we'll say fell off.....errrr no, it was stolen....yeah,yeah thats it :0 . I did not like the results on them as it made 0 increase in power or mileage. Plus on a jeep or like vehicle it will worsen fumes and will gag you when you run topless or with the back window rolled up if its a softop. Adding a 90 to make a side dump exhaust helps but all in all its not worth it IMO. BTW, regardless of smog laws in your state keep in mind it is illegal to remove any federally mandated smog equipment like cats unless its now used on closed course events so they say. Just sayin.

 

[88Sahara]

Thank you Gilaguy23. Useful observations. I'll dig a little deeper into my sitch and see if I can figure where the issue is. I thought about this because it looked like there might be a small gap in the pipe near the cat. Love having my soft top rear window open. Interesting idea on the side discharge-I'll take a look at that too. Much appreciated.

 

[cas]

Federal law aside... pipe for my old one let go so I used my YJ for about a week this spring without it. (temp pipe all the way to the rear. The exhaust fumes were so bad didn't want to drive it. I didn't even try to fix the old one cat, i bought a new one ASAP and installed it. So happy I did.

I've had several pre-cat cars and never noticed it before, but of course they all had tops and windows, doors and a longer wheel base.

 

[cas]

...it is illegal to remove any federally mandated smog equipment like cats unless its now used on closed course events so they say.

Even that is been brought into question now by the EPA, starting to little by little say "if it ever had it, it must have it" no matter how or where you use it.

 

[jeepjoe43]

Ordinarily I would say screw the EPA, but eliminating modern cats doesn't really do anything for power.
Just put an entirely new system on mine, including the cat, just because I like it quiet.
Brand new factory system from Rock for about $300 and it fit like a glove.
Had loud Jeeps in the past, but now I like being able sneak in a 2:00am and not wake my neighbors.

 

[Flyer58]

Ordinarily I would say screw the EPA, but eliminating modern cats doesn't really do anything for power.
Just put an entirely new system on mine, including the cat, just because I like it quiet.
Brand new factory system from Rock for about $300 and it fit like a glove.
Had loud Jeeps in the past, but now I like being able sneak in a 2:00am and not wake my neighbors.

My '92 2.5 started getting loud so I crawled under it today and found a really ugly repair weld finally gave up. The original cast exhaust header is still good so I'll replace everything from it on back.

Is the Rock Auto kit an relatively easy install and did you have to weld the pipes together? The local shop is asking $600 for everything including the cat.

Here's what I found...

 

[jeepjoe43]

My '92 2.5 started getting loud so I crawled under it today and found a really ugly repair weld finally gave up. The original cast exhaust header is still good so I'll replace everything from it on back.

Is the Rock Auto kit an relatively easy install and did you have to weld the pipes together? The local shop is asking $600 for everything including the cat.

Here's what I found...

View attachment 117907

Well, that it definitely shot!

The Rock kit did NOT require welding, all bolt in.
The cat was not part of the pipe and muffler kit and had to buy it separately (still figured in to my overall cost).
For me it was an easy install, but I had mine on a lift with the skid pan and T-case out.
This all happened in the middle of my SYE install, clutch, gas tank and D35 replace.
Might be easier to just take it to a shop if it's worth it not to do the job on the ground.

If you have just one sensor, the bung for the O2 sensor on the Rock stuff head pipe will be there but the pipe will NOT be drilled.
I guess that's so it fit's later models with multiple O2 sensors fore & aft of the cat? I don't know which yours is.
Thought mine was the latter and bought 2, but it ended up having just one.
Anyway, I didn't discover the pipe on mine til I had it in, and I decided to just pull the plug in the manifold and put it there.
Now I occasionally get code 52 (lazy O2 sensor) may have something to do with that.
You wouldn't think moving the sensor 4" would make any difference.
Tip, get all new nuts & bolts for the head pipe and the cat. I found mine at ACE, and it saved a lot of headache.

 

[machoheadgames]

With a 92 it should be bolt on. the cat should be flange-bolted to the downpipe with 4 bolts. The muffler will clamp onto the back of the cat and the pipe onto the back of the muffler. Once you clamp it all down, it will probably somewhat crimp together, so you probably won't ever want to remove any of it unless you plan to cut it apart and either or weld back together after or order new parts again, but usually you don't need to disassemble any of it anyways so not a big deal.

I like and use the Magnaflow cat and catback, but they are way too expensive. I like the catback though because it uses band clamps and slotted pipes so they can be tightened without crimping so it's all easy to take apart later. Easy is relative though, it all still rusts and becomes a bitch to remove regardless, so I try to avoid doing exhaust work in general if I can. That's why I bought the stuff with the intention of not touching any of it for a long time, then sawzalling apart later and buying new if I need to.

 

[machoheadgames]

Well, that it definitely shot!

The Rock kit did NOT require welding, all bolt in.
The cat was not part of the pipe and muffler kit and had to buy it separately (still figured in to my overall cost).
For me it was an easy install, but I had mine on a lift with the skid pan and T-case out.
This all happened in the middle of my SYE install, clutch, gas tank and D35 replace.
Might be easier to just take it to a shop if it's worth it not to do the job on the ground.

If you have just one sensor, the bung for the O2 sensor on the Rock stuff head pipe will be there but the pipe will NOT be drilled.
I guess that's so it fit's later models with multiple O2 sensors fore & aft of the cat? I don't know which yours is.
Thought mine was the latter and bought 2, but it ended up having just one.
Anyway, I didn't discover the pipe on mine til I had it in, and I decided to just pull the plug in the manifold and put it there.
Now I occasionally get code 52 (lazy O2 sensor) may have something to do with that.
You wouldn't think moving the sensor 4" would make any difference.
Tip, get all new nuts & bolts for the head pipe and the cat. I found mine at ACE, and it saved a lot of headache.

That's weird and dumb because all of the 91+ YJs have one single upstream O2 sensor and they're all the same thread. Sounds like laziness on the manufacturer's part.

Late TJs had precats with sensors fore and aft of each cat and then another sensor at the main cat, but they had a completely different exhaust manifold, completely different sensors, downpipes, and cats so who knows why they didn't drill the YJ pipe from rockauto.

 

[Flyer58]

That's weird and dumb because all of the 91+ YJs have one single upstream O2 sensor and they're all the same thread. Sounds like laziness on the manufacturer's part.

Late TJs had precats with sensors fore and aft of each cat and then another sensor at the main cat, but they had a completely different exhaust manifold, completely different sensors, downpipes, and cats so who knows why they didn't drill the YJ pipe from rockauto.

My guess is the same head pipe fits earlier models without an O2 sensor and yes they just leave it up to the owner to drill the hole based on what they have.

I'll add up the numbers and see what the total price is and if it's within a few hundred of the estimate I got then I'll have them do it. I dont have a lift but I did build up some nice wheel cribs which give me an extra foot of space underneath. It's becoming a familiar sight looking up while lying on my back.

Thanks for the help.

 

[machoheadgames]

My guess is the same head pipe fits earlier models without an O2 sensor and yes they just leave it up to the owner to drill the hole based on what they have.

I'll add up the numbers and see what the total price is and if it's within a few hundred of the estimate I got then I'll have them do it. I dont have a lift but I did build up some nice wheel cribs which give me an extra foot of space underneath. It's becoming a familiar sight looking up while lying on my back.

Thanks for the help.

Ah, I totally forgot about it likely being for the older carb and TBI models. That's probably exactly the case. Good luck with it. You may not even need to change the downpipe if it isn't rusted so bad that you can get it apart from the cat after unbolting.

 

[Gilaguy23]

My '92 2.5 started getting loud so I crawled under it today and found a really ugly repair weld finally gave up. The original cast exhaust header is still good so I'll replace everything from it on back.

Is the Rock Auto kit an relatively easy install and did you have to weld the pipes together? The local shop is asking $600 for everything including the cat.

Here's what I found...

View attachment 117907

Ouch... Geez, $600 for a new muff and cat? How times have changed. I paid $130 for a new tailpipe and muff 6 months ago on my 91. A cat is only $100 more. And to think I used to have manifold back dual exhaust with Turbo's and tailpipes out the rear put on a full sized 4x4 truck $250. Guess Im starting to really see what my 95 year old dad meant about not grasping today's prices of goods and service.

 

[Flyer58]

Ouch... Geez, $600 for a new muff and cat? How times have changed. I paid $130 for a new tailpipe and muff 6 months ago on my 91. A cat is only $100 more. And to think I used to have manifold back dual exhaust with Turbo's and tailpipes out the rear put on a full sized 4x4 truck $250. Guess Im starting to really see what my 95 year old dad meant about not grasping today's prices of goods and service.

Yes but that's the total price $600 for everything after the cast iron header to the tailpipe and includes a new cat. I think the cat alone was $300 but I want it included. What I've found in a limited search is close to $400 for the complete kit and my labor.

 

[jeepjoe43]

My guess is the same head pipe fits earlier models without an O2 sensor and yes they just leave it up to the owner to drill the hole based on what they have.

I'll add up the numbers and see what the total price is and if it's within a few hundred of the estimate I got then I'll have them do it. I dont have a lift but I did build up some nice wheel cribs which give me an extra foot of space underneath. It's becoming a familiar sight looking up while lying on my back.

Thanks for the help.

Hadn't thought about that...