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  1. #1
    Master Mechanic
    KyleZ71's Avatar
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    Jun 2010
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    York and Wilkes Barre, PA
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    Unhappy P0420 - Need New Cats

    Had the stupid P0420 code for some time now, but I've always been able to shake it... until recently. Knowing that there could be many causes I stopped by Monro Muffler and had them hook it up to their computer. Told I need new cats... When asked how much they charge for one they said they replace the whole y pipe and that runs $975 (summit sell the whole y pipe units for around 470). I know cats can be cut out and welded in (even though they said they can not) what would you all recommend? New cats or the whole y pipe unit itself? Since they need replaced I was thinking of just going with magnaflow or flowmaster highflow replacemets. Thanks all!
    Objects in mirror are losing

    2003 Chevy Silverado Z71, 5.3L, K&N 57 series, 2.5'' Flowmaster Super 10 series dual exhaust , Corvette Servo, McNew Automotive Dyno tune, SS gauge cluster, Extang Trifecta Tonneau, Pacesetter shorty headers, Goodmark cowl hood, Sony Xplod speakers, Kenwood DDX-470 exhaust tips, 16" Ultra Badlands polished wheels, Pirelli Scorpion ATR .

  2. #2

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    I bought the Magnaflow y-pipe with the high flow cats. Easier IMO to just do that than pay $100 per cat and pay someone extra to weld them in. Just Bolt the new pipe in yourself...

    I'm running that y-pipe with no muffler on my 5.3, just a resonated tip and it sounds SWEET. Not obnoxious; nice, deep, smooth tone.

    I think I paid a little over $425 for mine through advanced auto. Ordered online and picked up at the store, they have discounts all the time.

  3. #3
    Legend
    TRPLXL2's Avatar
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    Default

    Summit Racing has the Magnaflow High flow cats for $60.97 each, that is there normal price as I just bought 2 of them. You would just have to have someone weld them in, only thing I would recommend is remove the 02 sensors BEFORE welding or you'll be replacing them as well.
    2004 Chevy Colorado
    LS1 5.7 swap/TBSS rear axle swap

  4. #4

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    I did this research for my truck because my pass side converter is dead and keeps throwing a p0430 code. It is actually cheaper in the long run to just replace the y pipe and converters then buy them individually. I was looking at both Magnaflow and Flowmaster which are both about the same price, But you will need new O2 sensors. Actually either way you may need new ones because a bad cat can kill them.

    1996 Chevy Tahoe LT 5.7L V8 4X4 205,000+ miles. Built proudly at Janesville Assembly in Janesville, Wisconsin
    Basic mods: Lights all over, bunch of electrical work, and a couple cooling mods.

    Check out my other mods in My Garage: http://www.gmtruckclub.com/forum/sho...t-Tahoe-4-Door

  5. #5
    Sr. Engineer
    Join Date
    Oct 2010
    Location
    Indianapolis, In
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    493

    Default

    Whatever way you go, be sure to keep the old cats. and take them to a salvage yard (scrap metal) to sell them and recoup some of your money
    2000 GMC YUKON SLT, 5.3L tow pkg, G80 rear/w 3.73 gear

  6. #6

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    Quote Originally Posted by Conlan Rose View Post
    I did this research for my truck because my pass side converter is dead and keeps throwing a p0430 code. It is actually cheaper in the long run to just replace the y pipe and converters then buy them individually. I was looking at both Magnaflow and Flowmaster which are both about the same price, But you will need new O2 sensors. Actually either way you may need new ones because a bad cat can kill them.
    Cheaper, maybe... Easier, definitely.

    Plus it just sounds great. when you combo it with a straight through muffler or none at all!

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