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Bad cat converter?

This is a discussion on Bad cat converter? within the General Help forums, part of the LSx Technical Help Section category; Hi guys, Is there is an easy way to tell is your OEM cats are getting to the point they ...

  1. #1
    Senior Member JayTA98's Avatar
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    Bad cat converter?

    Hi guys, Is there is an easy way to tell is your OEM cats are getting to the point they need replacement? I have the rear o2 sensors deleted so I will never see a code. I don't hear anything out of the ordinary but within the last year I'm starting to notice some loss in power at acceleration. The car has 130k on it and it looks like it has the original cats on it.

    I replaced the front O2 sensors last year with bosch 13111's and i noticed better gas mileage. I don't have headers and I will like to just keep the stock manifolds for now unless I don't have another option. Tune up was done last year and new plugs and wires were installed. MAF gets cleaned every oil change.

    If i have a bad cat, how hard is to gut them and will the exhaust smell be stronger with a gutted cat? Will the exhaust sound change with a gutted cat? Are there any universal cats that work with stock manifolds that will not cost an arm and a leg? I have borla exhaust as well. Thanks.

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    Not sure how a gutted cat would sound on our cars. I do have one left from our car -- it is a GM warranty replacement with less than 20,000 miles on it. Just can't remember which side I still have and which one I sold.

  3. #3
    Former Mopar Man 2002ssslp's Avatar
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    I you have a buddy in the car repair trade maybe you can get him to hook you up to a sniffer ( polution tester ) if they have one. 130k is about the right time for a cat to go out. You can go several different ways with this but since you live in Florida I would just replace both cats. Get the one from Jeff and buy the other. That should be the cheap way out.
    My ride is a 2002 Camaro SS SLP #3296 with 30k, LTH, 3" Y, CME, Frost tune, K&N, ported TB, Blackwing lid, Bellows, MSD, Denso Iridium, and 85mm MAF, Bilsteins, Eibach springs, SLP strut brace, Adj. Panhard, TA Girdle, UMI, Pro 5.0, Nitto NT555
    My wife has a 2004 GTO with the rare SAP, 18" wheels, K&N Cold Air System, MSD, Ported TB, Frost tune, Denso Iridium, Flowmaster cat-back, 3200 Yank, 75k

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    Senior Member Too Fast's Avatar
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    ^^^yes a sniffer will tell if the converter is not cleaning the exhaust, but won't necessarily tell if it's clogging. The best way is to do that is with an exhaust backpressure check. Remove the upstream O2, rev the engine to 2500 or so, and you should not have more than 2.5psi. Closer to 0 is better. If it slowly increases with no RPM change, suspect some restriciton in the exhaust.

    Another way to check for restricted exhaust, with a vacuum gauge:
    Check the idle vacuum. Get a good manifold reading somewhere behind the throttle body. A good spot would be the fuel pressure regulator.
    Now, keep a steady 2500 RPM or so. The vacuum should be somewhat higher at that speed. 1-2'' more vacuum. It should never be lower than idle vacuum.
    Typically if your exhaust is restricted, the vacuum will start decreasing at the higher speed, with no RPM change.

  5. #5
    Member DaddySS's Avatar
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    Magnaflow (Carsound) direct fit cats have good flow at a reasonable price. At 130k it may be worthwhile to just replace them.

    MagnaFlow Catalytic Converters - 49-STATE & CANADA Catalytic Converters For Trucks, Suv's, American Muscle, Diesel, & Sport Compact Vehicles

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    Member RONS98TA's Avatar
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    If you gut the stockers it will have a strong carbon smell BUT will increase horsepower and fuel milage. (due to less restriction) Of course this is not street legal. I don't think i have ever had a car that didn't have the stock cat gutted. The sound will be a little louder than stock, but not unbearable.

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    Senior Member tatertot91's Avatar
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    Gut em out
    No emmisions check in florida, exhaust will get a little louder though

  8. #8
    Senior Member JayTA98's Avatar
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    Thanks for all the replies guys. I looked at those magnaflows direct replacement but we are talking close to $500 for both sides. I might gut them out before I decide to replace them. I have a very sensitive nose and I just hope the smell doesn't get too strong. I will love to do headers one day but I don't want to spend alot of money on them and i hate when the car rubs against speed bumps and corners. I was looking at the BBK's from summit.

    If the noise gets too loud I can close the tip since the borla comes with different size plates. I don't mind the noise as long it doesn't sound like crap lol.

    Is it pretty easy to gut a cat? I read you just get it out and use a prybar or screwdriver, destroy the material and vaccum it out?

    What about the exhaust gaskets? Do they break when you pull the cats out?

    I have to get the bolts loose as well hopefully they come out. I will use PB blaster overnight.

    I'm trying to not put too much money on this unless is completely necessary. I have to redo the leather seats as the leather is torn out. I might get another car or sell this one in the future. Honestly i love my TA but is not too comfortable and I need a bigger trunk. This might happen after October so I still have time to think about it.

    Sorry for the late response but I was in Palm Beach this weekend. I also changed the engine oil and did the tranny flush.

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    Hope everything comes apart ok for you. I gutted one years ago using a crowbar.

  10. #10
    Senior Member JayTA98's Avatar
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    Quote Originally Posted by pajeff02 View Post
    Hope everything comes apart ok for you. I gutted one years ago using a crowbar.
    Thanks Scott. I will try this as soon as i got some time this week.

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    Quote Originally Posted by JayTA98 View Post
    Thanks Scott. I will try this as soon as i got some time this week.



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    Senior Member JayTA98's Avatar
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    opps sry I meant Jeff.

  13. #13
    Senior Member JayTA98's Avatar
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    off the topic a little but are old cats like mine worth anything to a scrap metal yard or someone else?

  14. #14
    Senior Member tatertot91's Avatar
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    You should be able to get at least 30 bucks for the two. Ask around and maybe you can get a little more

  15. #15
    Senior Member JayTA98's Avatar
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    I have been searching around for some info about gutted cats on ls1s. so far I keep finding to it will sound like crap. im might just have to get headers. I have been looking at bbk. it not a bad price and it includes the ory. im not sure about ebay headers I see mixed reviews. I shoudnt need to tune the pcm since frost deleted the rear o2 or do I?

  16. #16
    Senior Member JayTA98's Avatar
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    I shouldnt get any gas smell inside the car with the a/c on and windows up right? lt just smells outside by the rear?

  17. #17
    Senior Member tatertot91's Avatar
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    You shouldn't notice a difference unless you have the windows down and are sitting at idle. A buddy of mine ran the bbk setup and was pretty happy with it. If frost deleted the rear o2s then you should be fine, woul will however need longer upstream o2s or extensions to reach the bung by the collectors.

  18. #18
    Senior Member JayTA98's Avatar
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    I have the longer o2 already installed. I guess i need to get 2 new gaskets for the headers. can re use the same manifold bolts?

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    Senior Member theorangeguy's Avatar
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    Quote Originally Posted by JayTA98 View Post
    off the topic a little but are old cats like mine worth anything to a scrap metal yard or someone else?
    They have a pretty high value to the right buyer...people steal them off of cars because of the prices people pay for the material inside of them.

  20. #20
    Senior Member JayTA98's Avatar
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    Quote Originally Posted by theorangeguy View Post
    They have a pretty high value to the right buyer...people steal them off of cars because of the prices people pay for the material inside of them.
    ok thx

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