Although this isn't an overly complicated job, it is a giant pain in the rear and took me a year to build up motivation to do. On top of all that, it's not really a mod but a required (and expensive) maintenance item that many are faced with regularly. So, I documented it to the best of my ability!

Step 1:
Start PB-blasting any/all exhaust nuts and bolts in preperation for removal; I'd start in on this at least 24 hours in advance, but even a week out is realistic. These things see a lot of heat, cold, and road stuff. This is also a good time to start building motivation

Step 2.1:
Collect all the necessary parts for your CC swap. I was able to find a used, re-certified CC, but many use aftermarket setups (e.g., magnaflow) just as well. This website has some really helpful part diagrams for our rigs, here's a link to the one I used. For my swap, I was removing the entire CC assembly and would only need the hardware and gaskets at the header and muffler (not the middle joint):

Header-CC gasket: 17410B
Header-CC Nuts (3): 17401A
CC-Muffler gasket: 17451
CC-Muffler Bolt (2): 90105-10388
CC-Muffler Nut (2; I did not use the retainer thing): 90179-10133

Step 2.2:
Collect your tools -->

14mm socket (deep and regular)
12mm, 19mm, & 10mm sockets
Breaker bar
Short and long ratchet extension
14mm wrench
Grinder w/cutting wheel
Big Flathead (for stretching the exhaust hangers)
BFH

Step 3: Grab a drink, beer, wine, whatever... assuming you're of age and/or your guardians approve.

I personally started with 3 of them (Pendelton's + Avery White Rascal*2) because I really was not looking forward to the job - I knew it was going to be a PIA! Whiskey is a known lubricant too.

Step 4:
Remove the crossmember and that hanging weight thing (transmission harmonic balancer?). These will need to be out of the way to actually get the CC assembly out of the truck (and the new one back in).


Step 5: Start removing the CC at the front end because it's likely you'll have to cut off the rear bolts. The way it was attached to the header was a bit confusing at first inspection, but hopefully this picture helps with that. The bolts are threaded into the header flange and there is simply a nut on the CC side of things.


I got at it from underneath, using a deep socket, two extensions, and a breaker bar (watch the knuckles!).


Step 6.1:
You can certainly try to remove the bolts/nuts from the rear flange, but there wasn't really any hex left on mine, so I suspect most people will have a similar situation. Bust out this stuff and get to town on the bolt heads!


Step 6.2:
Make sure your beer isn't warm.

Step 7:
Get to cutting, then separate the CC from the Muffler.


Step 8:
Disconnect the CC assembly from the rubber hanger things and gracefully slide it out from under the truck. Celebrate your progress and the defeat of that POS broken CC!


Step 9 (optional):
Remove the AF and O2 sensor to install on the new CC. Mine had been replaced prior, so I knew they were still good. If yours are old, it's best to just install new ones and not worry about taking them out of the junk CC (plus it's another huge PIA if they are old).

Step 10:
Install new CC under truck, connect to the rubber hangers, and position gaskets in their respective places.

Step 11:
Using new nuts, connect the CC to the header; using new bolts and nuts, connect the CC to the muffler. Not sure what the torque is (36 ft-lbs?), but make sure you don't have any leaks.

Step 12:
Connect the AF and O2 sensor to the plugs on the truck, re-install the transmission weight thing, and re-install the crossmember.

Step 13:
Start up the truck and make sure there aren't any exhaust leaks. I used a receipt (because it's a really light paper) and held it near all the joints to see if I was getting any exhaust leaks.

Step 14:
Enjoy the CEL-free life and perhaps a few MPGs returned to you!

Nice. Added to my how-to library.

Thanks for this! Bookmarked for later.

Well, I cut the two cats apart so I could see what was going on inside, hopefully get a little perspective on the root cause of the CC failure and mpg hit... it was pretty obvious from the rattling, but getting a look at it puts it all together. The back half of the front CC was melting and breaking off in large quantities only to likely plug up the downstream CC. The pic doesn't quite do it justice, but here you go!



Also, thought I'd share a pic of my buddy who hangs out and helps (or just barks at strangers and tries to "talk" to me):

Thanks for the info, writeup and photos!

Very nice write up, I've also been pushing this much needed job to the side cause I don't want to deal with it! Thanks man!

I see you used a "recertified" cat? Where did you purchase this from. I will be needing one to correct my Po420 code and don't really want to drop the bucks on a new one.

I got lucky and this place in St. Cloud, MN just happened to have one for my truck. They're called Recatalitico. I don't know how often they get 4Runner cats in, but worth a shot. Mine is still working... knock on wood!

Meh, I had someone remove mine for me...let the insurance company buy me a new one... :P

I couldn't find a remanufactured unit so I had to take it to the local muffler shop and have them replace both cats. They used AP cats so hopefully this will work out okay.

Not the most exciting way to spend 300 bucks but definitely cheaper than OEM.

Fingers crossed!

Nice little write-up. And props for drinking Avery's, they are my favorite brewery. I visited them in college and the brew-master chatted with us for 3 hours about beer while another guy named Tank popped open bottles of every beer for us to try while we talked. There is 1 store near me here in Boston that carries them regularly, but only the Samael, the Czar, and the white rascals, and I think they dropped those recently.

I had way more rust then you did, and had to cut off the posts in the header. I then cut out a chunk of the header flange from the bolt holes outward, so exposing the stud, knocked the studs out, then bolted on the new cat using bolts and nuts. It is holding just find so far.

I also didn't take the cross member off, so I had to split the cat's under the vehicle to get them out.

Mine also had a detached honeycomb in one of them. The other was ok. I might have been fine with just cleaning out the cat's (I have heard that you can soak them in laundry detergent to clean them), but for a big a PITA the removal was, I wanted to make sure I was solving my problem, so I bought some new Eastern Catalytic cats and they have worked to shut off the CEL.

Awesome write up, I'll definitely be using it. Do you know what brand catalytic converters I can use that will get rid of my CEL?

It depends on a few things - year, engine, your state, etc... Eastern and Walker are the two that come to mind though. Magnaflow makes them too. In either case, there's a lot of anecdotal evidence that any aftermarket one might only keep the CEL off for a year or two, but that's ok. Mine had pretty much rotted out, so it was needed for performance as much as for the CEL.


Avery is one of my favorites too, especially of the Colorado breweries! I can never remember which one, but one of their bombers is the stuff of legends. It's tasty and strong. I sold them my used receiver from my home theater to use in their refrigerated storage room. I was asking $35 or something and they hooked me up with 2 cases and one of each bomber... which is probably worth $90! Amazing deal. Oskar Blues is another great CO brewery and I noticed they had their Pilsner on tap last time I was in the Newark airport - so they're making some decent distribution.

I have a 2001 in PA. My main concern is getting the CEL off without breaking the bank. My exhaust needs replaced entirely, its old rusted and leaking.

Whereabouts are you located? I went to Red Run Exhaust. They have two locations, both in Lancaster county. They are awesome, have done a bunch of work for me, very well recommended and great pricing.

It was $315 for them to replace both the cats.

This is the brand they use, AP Exhaust | Automotive/Light Truck Exhaust Products | Heavy Duty Exhaust Products | Emission Products
and say they've had the best luck with them. These guys are a specialty exhaust shop, that's all they do.

Like I said, fingers crossed that this works and lasts at least a few years.