OEM Catalytic Converter Replacement

I have come to the realization that my dream of a LS engine swap are just dreams. I have been putting off replacing my exhaust for the past three years in hopes of replacing everything with the engine swap.

Now I'm about to replace my entire exhaust due to age (9 years old), and the P0430 error code that I've gotten repeatedly over the last month (that will magically clear itself and then come back). So while I'm in there I'm going to replace my spark plugs and wires.

I just bought a set of JBA headers and the Dynomax Evolution Competition Cat-Back Exhaust System
(Part # DYN39516) (based on Eddie's past experience). I getting ready to purchase the OEM catalytic converter, spark plug wires and the wire holder.

Does anyone know if the OEM CAT comes with new O2 sensors? If not should I buy new ones...I'm assuming my current O2 sensors work.

For those who have done it on an older JK, is there anything else that I should consider doing while I'm "in-there"?

Thanks in advance!

No cat comes with HO2S. I would buy the 2 upstream and 2 downstream HO2S from the dealer or online, but do not
install aftermarket HO2S. Do you have an exhaust leak or misfire problems ?

Buy new OEM sensors, they have a shelf life like motor oil, sure they will still work but are not doing as great of a job. I have been told by good mechanics that 85k is a good life span for an o2 sensor. Maybe they are full of shit, maybe not, but if you are already replacing everything else why put some old questionable stuff back in?

Good point guys. I wanted to make sure the O2 sensors didn't come with the CAT. I figured they didn't, but I wanted to be sure so I wouldn't spend the money and not need them.

I'm not having misfire issues, but I've had multiple exhaust leaks over the past 3 years that I've welded up. I've been putting bandaides on the exhaust system for the past couple of years and it's time to just replace it completely. The Jeep on has 79k on the odometer, but it was in New England for 6 of its 9 year life so far.

Does anyone know the bolt size, length, pitch and harness for:
- the exhaust manifold bolts to the 3.8L engine
- catalytic converter to downstream exhaust pipe

I found the torque specs on Project JK, but I can't find the fastener specifications.

I want to pick them up from fastenal before I start the entire exhaust replacement project.

Thank you in advance!

Ok never mind on the fastener size for the headers to engine since the JBA headers just arrived with new bolts, but not the gaskets...


That's ironic...

MattAlpha said:

Ok never mind on the fastener size for the headers to engine since the JBA headers just arrived with new bolts, but not the gaskets...


That's ironic...

Click to expand...

Many times headers go on with NO gaskets. Check the instructions to see.

Just curious to what year and how many miles you have and where you leak is? There is a federal emission warranty. If it's a design or material failure that leads to an emission leak then it must be repaired by the manufacture for free. It is for 8 years or 80000 miles. I had a Crack between my manifold and cat and had it replaced for free by dealership.
I know you already bought your stuff but... Google it if interested.

Thanks for the heads-up about potentially not needing a gasket. I'll go through the instructions for the headers in the morning.

I have a 2007 with 79k on it. I've welded the y-pipe a few times to correct leaks. The catalysts both rattle as does the muffler when the Jeep is cold and coming off higher RPM. 5 of the 9 years the Jeep lived in CT and RI. 8 of 9 years on the east coast or west coats. It's seen more than its fair share of salt. It's been throwing the P0430 code intermittently for the past two months. It will clear then come back and could be the catalyst or an O2 sensor. I also wanted to put to put on a muffler that dumps before the axle. So instead of trying to see if the dealership would cover it, I just bought the parts. I figured they probably wouldn't cover it, but I'll never know now.

MattAlpha said:

Thanks for the heads-up about potentially not needing a gasket. I'll go through the instructions for the headers in the morning.

I have a 2007 with 79k on it. I've welded the y-pipe a few times to correct leaks. The catalysts both rattle as does the muffler when the Jeep is cold and coming off higher RPM. 5 of the 9 years the Jeep lived in CT and RI. 8 of 9 years on the east coast or west coats. It's seen more than its fair share of salt. It's been throwing the P0430 code intermittently for the past two months. It will clear then come back and could be the catalyst or an O2 sensor. I also wanted to put to put on a muffler that dumps before the axle. So instead of trying to see if the dealership would cover it, I just bought the parts. I figured they probably wouldn't cover it, but I'll never know now.

Click to expand...

The headers may have come with some kind of sealant or it will direct you what to use.

The JBA instructions say to use re-use the original gasket (header to engine block) or a new factory gasket with "a little high-temp RTV silicone to the gasket."

I'll be purchasing new gaskets for the headers.

MattAlpha said:

The JBA instructions say to use re-use the original gasket (header to engine block) or a new factory gasket with "a little high-temp RTV silicone to the gasket."

I'll be purchasing new gaskets for the headers.

Click to expand...

Good deal.

MattAlpha said:

The JBA instructions say to use re-use the original gasket (header to engine block) or a new factory gasket with "a little high-temp RTV silicone to the gasket."

I'll be purchasing new gaskets for the headers.

Click to expand...

I used some of that high temp ultra copper stuff when I went through my exhaust to seal the joints and at the joints where the exhaust hooks on to the manifold (the collector) the stuff caught fire and burnt off. Not a huge fire but I went around the block and punched once and when I pulled back in the garage and lifted the hood to inspect I saw the flames down around that area on both sides. It didn't hurt anything and I just watched it closely as it burnt off. There is another joint about 1.5' away from the collector and the stuff is still there so apparently its cool enough just a little bit away from the collector to not light the stuff off. Point is, I wouldn't even dream of putting the stuff at the joint where the manifold connects with the head.

DKjeep said:

I used some of that high temp ultra copper stuff when I went through my exhaust to seal the joints and at the joints where the exhaust hooks on to the manifold (the collector) the stuff caught fire and burnt off. Not a huge fire but I went around the block and punched once and when I pulled back in the garage and lifted the hood to inspect I saw the flames down around that area on both sides. It didn't hurt anything and I just watched it closely as it burnt off. There is another joint about 1.5' away from the collector and the stuff is still there so apparently its cool enough just a little bit away from the collector to not light the stuff off. Point is, I wouldn't even dream of putting the stuff at the joint where the manifold connects with the head.

Click to expand...

Thank you so much for sharing...since I bought that exact High-Temp RTV for use with the gaskets for the headers to the engine block. I will be replacing the gaskets.

After that RTV burnt off did you have any exhaust leaks?

I finally had some time to get to this project. Patience, removing the fenders and my air compressor were mandatory not to mention PB Blasting all of the associated fasteners. The PB Blaster worked as it has for me in the past, no broken fastners. The new JBA headers, spark plugs and wires installed. I still need to replace the cat with new O2 sensors, which is waiting for the PB Blaster to work some more magic on the clamp for the cat and exhaust pipe to the muffler. Hopefully I'll get that off in the morning. This is the third thorough soaking, if it doesn't work the angle grinder will. Once the new cat is installed, I re-install the heat shields. Evidentially my muffler will get shipped and I'll be able to complete this project.

Passenger side before:


Passenger side Header removed and you can see the crack...:



Passenger side installed (I have the bolts to cat holding it on until I get the clamp past the Y-pipe off so I can replace it.:


Driver side before (top view):


Driver side header had more cracking and the cracks almost made it all the way around...just a bit scary. I couldn't see them until after I removed the heat shield.:




Driver side installed (top view):


Hopefully the rest of the project will go smoothly.