"You cut off your cat" question

[Brutus]

I'm getting ready for a trip next friday and don't have time to totally do a new aftermarket cat. I was hoping to cut the old stock cat off and replace with a length of exhaust pipe just until I get back and have a new one put on.
I know several here have cut their's off and several more have had them stolen. What I was wondering was how and where was it cut off? Like just in front of the cat and just behind, or in front of the forward O2 and just behind the rear O2?
I got under the truck a few minutes ago and was hoping I could just cut it off and fit about 19-20 inches of pipe on to it but just behind the cat, the factory exhaust has a funky shape that I'm not sure I could get the new one to fit to.
I also thought about trying to remove the nuts (cut off) on the flange and have a new pipe made up to match up with the flange.
Any thoughts?

I've recently noticed a sluggishness and loss of performance that I'm trying to fix. Plugs and wires are newish and I feel like replacing my cat might help. I'm willing to try it out anyhow. 268,000 miles on original cat.

Thanks.

 

[Doc2012]

All it's gonna do it throw a CEL, saying that your O2 sensors are bad, which is going to hurt your gas mileage because the truck won't be in closed loop operation. It will continuously be running in open loop.

If you're not throwing any CELs right now, then don't replace the cat. It should still be good. If you're going to do it, all the luck to you, but these trucks don't like aftermarket cars by them selves. You need a tuner of some kind to fool the O2 sensors to making them think it's the stock cat.

 

[fish0281]

All it's gonna do it throw a CEL, saying that your O2 sensors are bad, which is going to hurt your gas mileage because the truck won't be in closed loop operation. It will continuously be running in open loop.

If you're not throwing any CELs right now, then don't replace the cat. It should still be good. If you're going to do it, all the luck to you, but these trucks don't like aftermarket cars by them selves. You need a tuner of some kind to fool the O2 sensors to making them think it's the stock cat.

I think you're partially right. You will need the upstream sensor to function properly so I would cut after that or else your truck will not be able to read the AF mixture (it'll stay in open mode) and you'll run rich (which is the safe mode). The downstream one, theoretically, doesn't impact your mixture and only detects emissions.

If you have a bad cat the truck won't necessarily throw a code right away, but it definitely affects performance because it's either plugged, melted, or both. My front cat was $hit when I pulled it out and was missing about half the core, which means the debris was caught up in the downstream cat.

If you have time to cut out the cat and drop in a straight pipe, why don't you just bring it to the muffler shop and have them weld in a universal one? It'll only take about an hour and probably not too expensive ($100-$200?) - but the fix will not last as long as the original CC.

 

[BTO]

OP,

Why are you so fixated on the cat? Not a cat person? Could be any number of things causing your problem. Have you tried pulling codes? Rule out ignition and fuel delivery?

 

[steezemcqueen]

I cut mine out. Just did it right behind the front O2 sensor and replaced it with a piece of 2.5" OD pipe. Has more power, better MPG's, and no issues with how it runs. Every 500 miles or so it will trigger the P0420 CEL but its really not a big deal and i just clear it with the Ultragauge. You could install a sensor simulator if the CEL bothers you.

It is pretty loud without the cat though so i am planning on putting a universal one back in to quiet it down. I also have to get my truck emissioned in October so i will need to put one back in anyway

 

[cordrayj1]

I cut mine out. Just did it right behind the front O2 sensor and replaced it with a piece of 2.5" OD pipe. Has more power, better MPG's, and no issues with how it runs. Every 500 miles or so it will trigger the P0420 CEL but its really not a big deal and i just clear it with the Ultragauge. You could install a sensor simulator if the CEL bothers you.

It is pretty loud without the cat though so i am planning on putting a universal one back in to quiet it down. I also have to get my truck emissioned in October so i will need to put one back in anyway

steeze, do you have a cali spec 4runner? im in the same boat with that code. I have 246k on the clock and have replaced my stock muffler, which weighed about 35 lbs when i removed it. it was SOLID full of crap. i have a feeling my cats are extremely restricted. i may try that fix and see what it does.

 

[cordrayj1]

just found this: The Misleading Nature of the PO42O Code - Eastern Manufacturing

good info.

 

[Brutus]

I'm not throwing any codes nor have i ever since I've had this truck, 3 yrs plus. Just need/want better performance.

I don't trust the shop here in town, small town America, as they have bible quotes all over the place but if you ask them to cut off your cat, they get all quiet and ask "Who's gonna know bout this?" Everyone in town knows about it. I've had them do work for me before and I'm not goin back. Nearest big town is 30 miles and I rarely go that way.

Steeze, How long of a pipe did you go with? I thought 19-20" would be enough but not sure how it'll fit over that funky shape section in the rear.

 

[fish0281]

...I don't trust the shop here in town, small town America, as they have bible quotes all over the place but if you ask them to cut off your cat, they get all quiet and ask "Who's gonna know bout this?" Everyone in town knows about it. I've had them do work for me before and I'm not goin back. Nearest big town is 30 miles and I rarely go that way...

Completely reasonable, I would do the same.

 

[stevec5000]

I wouldn't cut it off for no reason. If you don't trust it then just take it off and have a look to see if it's in good shape. If it's not melted, burned, contaminated or plugged up like the photos in "The Misleading Nature of the PO42O Code" website shows and you can see through the holes and it looks OK then you probably shouldn't mess around with it.

 

[steezemcqueen]

steeze, do you have a cali spec 4runner? im in the same boat with that code. I have 246k on the clock and have replaced my stock muffler, which weighed about 35 lbs when i removed it. it was SOLID full of crap. i have a feeling my cats are extremely restricted. i may try that fix and see what it does.

Mine is a 97 so i only had the single cat. I hollowed out the rear cat on my old cali spec 2000 and it made a good difference as well.

Steeze, How long of a pipe did you go with? I thought 19-20" would be enough but not sure how it'll fit over that funky shape section in the rear.

I honestly don't remember how long it is. 19-20" sounds about right though. I basically just cut it right after the O2 sensor. I also cut just after the flange too because i didnt feel like the extra work to get the flange to work was work it so i just made it all one piece.

Here is a picture

 

[Toyotayoda]

Most exhaust shops will not cut off a catalytic converter because it is a federal crime, with fines for the shop and the owner of the car. You could be onto something with the catalytic converter being plugged, many times they can be plugged and will not throw a code, or give a misleading code like P0171. If the cat is broken inside than you might want to remove your muffler and check for debris, only one way for the stuff to go. A universal cat can be welded on pretty cheap, but will usually be degraded within a year.

 

[Twan]

Most exhaust shops will not cut off a catalytic converter because it is a federal crime, with fines for the shop and the owner of the car. You could be onto something with the catalytic converter being plugged, many times they can be plugged and will not throw a code, or give a misleading code like P0171. If the cat is broken inside than you might want to remove your muffler and check for debris, only one way for the stuff to go. A universal cat can be welded on pretty cheap, but will usually be degraded within a year.

It's been over 4 years. He's probably taken care of it by now.

 

[Toyotayoda]

It's been over 4 years. He's probably taken care of it by now.

I guess I should stop reading posts at midnight