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P0420 - Cat. Replaced, BUT NOW...

This is a discussion on P0420 - Cat. Replaced, BUT NOW... within the General Help forums, part of the LSx Technical Help Section category; A local dealer replaced my driver's side catalytic converter under warranty a few days ago, and now I have a ...

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    P0420 - Cat. Replaced, BUT NOW...

    A local dealer replaced my driver's side catalytic converter under warranty a few days ago, and now I have a very peculiar sound on start up and while cruising until the car warms up. It's a rumble that sounds almost sounds like a fast, low-pitch vibration, though I doubt anything is actually vibrating.

    I've never heard of needing to break in a catalytic converter so I'm not sure what's going on. Anyone have advice?

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    Ebaaaaaaaaa Speedy_Gonzales's Avatar
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    Take it right back to the dealer

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    Member jag42420's Avatar
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    Quote Originally Posted by SpeedAddict38 View Post
    Take it right back to the dealer
    +1 See what they claim it is...

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    1 01ls1ws6's Avatar
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    Weird, I had the same problem. The dealer replaced my passenger side cat and it would vibrate under acceleration. But the other day i was changing my oil and I found that i had a busted tranny mount. It fixed it and it totally fixed my problem. Thats probably not your problem though, take it back to the dealer, but make sure you let them know your pissed!! lol

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    Life in the Fast lane sunsetorangess's Avatar
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    Quote Originally Posted by SpeedAddict38 View Post
    Take it right back to the dealer
    Yepp i would have to agree
    J
    2001 SS, Its not the car its the Driver that matters....

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    Senior Member Danger731's Avatar
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    I HAD THE WARANTEE DONE LAST YEAR AND THEY left a bolt in my exhaust !, fn rattled around crove me nuts, fn dealership service.

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    Senior Member Danger731's Avatar
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    But why only one cat, they should have done both they were ALL recalled. rip off ?

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    Senior Member 35thAnniZ28's Avatar
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    loose bolt?

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    I have a need for speed! jigger1166's Avatar
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    Quote Originally Posted by Danger731 View Post
    I HAD THE WARANTEE DONE LAST YEAR AND THEY left a bolt in my exhaust !, fn rattled around crove me nuts, fn dealership service.
    It's not the dealerships fault, it's the technicians fault. There are bad techs. everywhere

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    I have a need for speed! jigger1166's Avatar
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    Quote Originally Posted by Danger731 View Post
    But why only one cat, they should have done both they were ALL recalled. rip off ?
    There isn't a recall on the cats. GM extended the warranty on the cats., and only replaces a cat. if it's bad.

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    I have a need for speed! jigger1166's Avatar
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    Quote Originally Posted by RandomOmen View Post
    A local dealer replaced my driver's side catalytic converter under warranty a few days ago, and now I have a very peculiar sound on start up and while cruising until the car warms up. It's a rumble that sounds almost sounds like a fast, low-pitch vibration, though I doubt anything is actually vibrating.

    I've never heard of needing to break in a catalytic converter so I'm not sure what's going on. Anyone have advice?
    It may be an exhaust leak. When the exhaust warms-up, the metal expands, and the gap where the leak is, closes.

    You need to bring it back to the dealer, and leave it overnight, so that they can hear it on start-up. If you drive it there, it'll be warm, and they won't hear the noise.

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    Okay, so, I did take it back. They adjusted my exhaust on the spot; the tech showed me where my magnaflow catback's plumbing was resting against the cross member near the rear on the passenger side. He apologized for me having to come back. Unfortunately, the adjustment only cured about 50% of the noise - I still hear it, though not nearly as much, and only from the rear driver's side.

    I need to take it back again, sadly. The customer service I receive at this dealer is pretty good, and friendly, but the worksmanship is only adequate.

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    caraholic ggino85's Avatar
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    i got both of my cats replaced about 1 month ago and when the car is warming up i can feel a rumbling sound from under the car where the cats are, it feels like popping popcorn. i asked my mechanic and he said it was just the cats warming up. my SS never did this but i never had a car with brand new cat eithier. does the cat warming up thing sound true or could this be another problem..........

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    Senior Member Danger731's Avatar
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    sounds like a bad cat, my new ones never did, when the car had 3 miles on it or after they were replaced

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    Member jag42420's Avatar
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    Quote Originally Posted by ggino85 View Post
    i can feel a rumbling sound from under the car where the cats are, it feels like popping popcorn. does the cat warming up thing sound true or could this be another problem..........
    Mine are the same cold and hot, no rumbling or sound variance. Same with my stock ones and my aftermarket high flows. Something doesn't sound right there...

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