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  1. #1
    Sr. Apprentice ras's Avatar
    Join Date
    May 2007
    Lebanon, In

    Default Cutting the cats off of my truck?

    I am considering cutting the cats off my truck and I was wandering if that would mess with my O2 sensor since its after the cat.
    99' Z71 extended cab 3 door

  2. #2


    Big mistake, and one you will soon wish you hadn't made.The bottom line is the truck will not run correctly without the cats or an o2 censer designed to make the computer think that they are there. With that expense in mind better off going with high flow cats. My 02.
    1997 Gmc Suburban SLT
    178k 2wd

  3. #3


    Their there for a reason.
    The way engines and computers are designed these days the truck wont run very well. Not to mention the check engine light your gonna get unless you use an O2 sensor tester on the O2 sensor.

  4. #4

    Join Date
    Feb 2008
    Red Wing, Minnesota, United States


    get high flow cats, you can find magnaflow cats on ebay for very cheap
    99 K1500 Suburban LT "THE BEAST"
    Hypertech III, K&N, true dual

  5. #5


    I understand your desire to increase flow for cheap, but unless you are willing to spend a few hundred dollars to add sensor bypass units, and have your ECM remapped, you're not really going to accomplish anything other than pollute more. You can add power by removing them, but it's expensive, and should only be a thought as a last resort to squeeze out a few extra ponies for the track or off road purposes. High flow cats are your best bet, with a decent cat back system to follow. You will get great sound, better performance, and best of all, tolerable emissions. Also my .02 cents

  6. #6
    Sr. Apprentice ras's Avatar
    Join Date
    May 2007
    Lebanon, In


    Well I'm not trying to get more power it just seems like the truck aint breathing right anymore and its gettin up there in miles. They have to be on there way out.

  7. #7
    Jr. Engineer
    Join Date
    Jan 2009
    Rochester, MN


    Contrary to what a lot of people think, it will not wreck the way your truck runs at all due to the O2 sensors. The ones before the cat are the only ones that affect engine calculations, the ones after the cat are only there to monitor cat efficiency. If you have a diablosport predator tuner, you can delete the O2 code from your PCM so the check engine light will not come on. If you think your truck isn't running right because of the cats, drill a hole in the exhaust pipe just before the cats and see if it runs better. If it does, then remove or replace them. If it still runs the same, have your drilled holes welded up and save the money you would have spent on replacing cats. If you remove them you will pollute more and you will probably not have as much backpressure in your exhaust so you could lose power that way, or so I've heard. I have a 98 regal that had a really leaky exhaust right after the cat, it would have been hard to replace the pipe after the cat while saving it, so I just hacked the cat off too. I didn't notice any loss in power or gas mileage.
    99 Silverado Z71 4.8
    2" Suspension lift (Add-a-leafs and leveling keys)
    Long tube headers with 3" offroad Y-Pipe
    Volant Cold Air Intake with Ram Air Intake Tube
    Jet Mass Air Flow Sensor
    Diablosport Predator Tuner

    Previous Truck:
    97 Suburban K1500
    3" Body lift
    2" Suspension Lift (Add-a-leafs and cranked up torsion bars)
    35" Yokohama M/T's
    K&N Intake
    Airraid Throttle Body Spacer
    Hypertech Programmer
    Dual Flowmasters

  8. #8


    Don't forget the 10,000 (each) fine from the EPA for getting caught removing them. I wonder if the moderator knows that the possibility of committing a felony is being discussed here.....

  9. #9


    Unless you had a diesel, I would recommend against it. If you really want to you can get some high flow cats like mentioned above, but I would highly recommend cutting them off.

    2005 Silverado - 4.3L, 5spd Manual, K&N Drop in Filter, Modded Air box
    Kenwood KDC-MP732 Head Unit, Pioneer 760W Amp, 2x 10" MTX Thunder 6000 subs, Uniden PC68XL CB/PA

    2004 Cavalier - 2.2L Auto
    Bone Stock

    1977 Toyota Celica GT - 20R (2.2L), 5spd, 146,000 Miles all Original (even the clutch)

  10. #10


    punch them out and put em back on....but you didnt hear it from me....

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