ebomberger Posted February 27, 2009 Report Share Posted February 27, 2009 The other day, while driving to work, I stopped to pay a toll and heard a loud "knocking" sound coming from underneath the truck when stopped and driving at low speeds. I pulled over and crawled around under the truck to see where the sound was coming from. I was freaking out, thinking it was rod bearings or somethings. When I got home and crawled under again, a found that there is something banging around inside the passenger cat. What the hell is causing this? If I remove the cats, will the truck run any differently until I get the PCM tuned? Quote Link to comment Share on other sites More sharing options...
Fireman31 Posted February 27, 2009 Report Share Posted February 27, 2009 Your cat is coming apart internally and needs to be replaced. If you delete the cats without tuning for it, your truck will run fine but will have a pesky CEL until you have the rear 02 codes deleted. Your cats are warrantied 8years/80,000 miles by Federal mandate, if you are within this, the dealer should replace your cats FOC........ Quote Link to comment Share on other sites More sharing options...
ebomberger Posted February 27, 2009 Author Report Share Posted February 27, 2009 A couple more things, the knocking is really loud, loud enough it turns heads. Also, when driving the knocking stops when I get above 40 mph. Thanks for the info fireman. Quote Link to comment Share on other sites More sharing options...
Ross Posted February 27, 2009 Report Share Posted February 27, 2009 The cats are shot! I had the same thing with my last truck. If you've ever seen the inside of a stock one it looks like a honeycomb material and that knocking your hearing is more than likely pieces that have broken up and are bouncing around from pressure and pinging against the cat housing. Replace em or ditch em - you're hp and mileage will suffer if you don't... Quote Link to comment Share on other sites More sharing options...
Krambo Posted February 27, 2009 Report Share Posted February 27, 2009 Replace them ASAP. If you didn't get a "check engine light" yet, you will shortly... Quote Link to comment Share on other sites More sharing options...
kcsilveradoss Posted February 27, 2009 Report Share Posted February 27, 2009 this is exactly what is going on with my truck, it will cause misfires eventually if it isnt already. that right hand converter is about 550.00 thru gm. i just ordered aftermarket exhaust from engine back yesterday... Quote Link to comment Share on other sites More sharing options...
SSThunder Posted February 27, 2009 Report Share Posted February 27, 2009 I agree with the group. You better replace it before it clogs and blows your engine. GM should do it for free. Quote Link to comment Share on other sites More sharing options...
mcmahan Posted February 27, 2009 Report Share Posted February 27, 2009 yea bro i just went through this. i deleted my cats and had pipes welded in place. you will notice a big gain in power or atleast i thought i did. lol good luck man Quote Link to comment Share on other sites More sharing options...
YenkoChevelle69 Posted February 27, 2009 Report Share Posted February 27, 2009 You won't notice a big gain in horsepower. Gains are minimal. Somewhere around 1-2-3 horsepower is all. Nothing noticable. I had the same thing happen. I ran a crow bar through my cats and then had my pcm tune accordingly. Mine got to the stage of causing the misfires. Not fun. Quote Link to comment Share on other sites More sharing options...
ebomberger Posted February 27, 2009 Author Report Share Posted February 27, 2009 The cats are gone! I put two flowmaster 40 series on. Sounds mean! Thanks for the advice fellas Quote Link to comment Share on other sites More sharing options...
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