Slackdaddy

Getting ready to stuff the new engine and trans in the 2001 XJ project.
I am not in California,,, Our emissions testing is a simple plug in the OBDII port test.

I need a complete exhaust from the manifold to the tail pipe.
Looking at the pieces on rock auto and I have a few questions:

The Pre cats run from $250 for Walker brand to $850 and everywhere in between,, why the big price difference?
One of the pre cats does not have the "Tri flange",, but has the long pipe welded to it ? https://www.rockauto.com/en/moreinfo...sn=426&jsn=426

In the shop drawings for the 2001 exhaust: https://parts.thomascdj.com/v-2001-j...exhaust-system
it shows either a rear cat converter OR a "resonator" what is the difference and why?

Thanks,
Slack

Slackdaddy

I did a little more digging, here is a shot of the 2001 parts manual,, it looks like the rear Cat IS required, the resonator is for leaded fuel.

Randy Bobani

https://www.rockauto.com/en/moreinfo...73666&jsn=1025

I hit this kit with Cerakote and slapped it on my 00'. I needed a 2.25" band clamp to connect the muffler outlet to the tailpipe. I also chopped a few inches from the tip of the tailpipe and I put an aftermarket tip on it. You'll need a rear Cat as well.


https://www.rockauto.com/en/moreinfo...73666&jsn=1036

It's holding up very well. I didn't bother replacing the front Cats. I've pulled a few front Cats from 4.0L Jeeps and have never seen them have any significant issues. But if you really want to replace them and the O2 Sensors, I would recommend the Walker part because I know it won't have any fitment issues and I use NTK O2 Sensors only.. The reason why you see some differences in the aftermarket front cat parts is simply due to some manufacturers opting for a one piece design rather than the three bolt flange. There were also different Cherokee models per the emissions standards to where the new Jeep was being shipped. Strange time with all these conflicting emissions laws.

https://www.rockauto.com/en/moreinfo...73666&jsn=1037

Ralph77

The big thing about a CA Emissions '01 is where you live.
So there are front dual cats, what I believe you are calling the pre cats, that can't be used in states like CA.
The front dual cat that I put on my '00 is cheaper then the one I would of had to use if I lived in CA.
The list of states that abide by CA rules is constantly changing. But to the best of my knowledge MD is not one of them.
So I am thinking that is why you are seeing the price differences that you are.

So as far as the rear cat/resonator goes #7 in your illustration appears to be for leaded fuel.

As far as the RockAuto link you posted with the combination front cat and front pipe.
I believe that Jeeps came from the factory with it like that.
Here is a shot that I grabbed off a Craigslist ad where a guy was selling one.

Now when I replaced the whole exhaust on my '00 with CA Emissions it was not set up like that.
I had a separate front cat and front pipe. So I have never really been sure what to make of that.
I assumed my exhaust was original but.......

So to bottom line it since you are replacing the whole exhaust and live in MD you will use all the part from the first link at RockAuto
that Randy posted. If you can afford it I recommend using the QuietFlow muffler, 21489, instead of the cheaper 18959.

Those parts in that link are the exact parts that I used.

Now a couple things. There is a hanger on the tail pipe that you will cut off. That hanger is there so it can be used with most, if not all, Jeeps.
In older Jeeps the hanger set up back there is different.
Also the hanger that you would use for your Jeep, 36377, is bolted to a nut strip that you have in your uni-body.
So if you don't have to mess with it just cut the muffler clamp to remove the tail pipe.
Cause if you do you might find that you have to replace the nut strip. And that requires removing the rear bumper.

Also all the nuts and bolts you need can be bought at the hardware store.
The front of the muffler has studs on it so you will just need nuts and washers there to connect it to the rear of the rear cat. Also can be bought at a hardware store.
Now if you can find flange head nuts and bolts to use all the better.
I used regular ones with washers. But I had to grind down a side of a washer or two so it would fit and lie flat in the flange.
If you mock this up before you install it you will understand that better in case I am not explaining it well. LOL.

You can use a traditional muffler clamp for the back of the muffler and the front of the tail pipe.
Randy posted that clamp at Amazon.
I say if you are going to go that route use this one instead.

https://www.napaonline.com/en/p/BK_7...dInput=7333972

See how it is stepped? That is the one I used.
See my QuietFlow comes with a lifetime warrranty. I used that clamp because I figured it would not crush the pipes together like a traditional one.
Since if I ever have to warranty my muffler maybe I can separate it from the tail pipe and not have to buy a new one.
Maybe. LOL.

And last I bought brand new hardware from dealership for where the front cat bolts to the exhaust manifolds.
6505754AA and 6506546AA. 4 of each.
I might not have needed them but figured it was just better to have them just in case.
Also guessing you could use nuts, bolts, and washers here but.............