Booreatta Posted June 18, 2011 Share Posted June 18, 2011 My cat converter has a horrible rattle. The question I have is what problem if any if I cut the guts out of the cat and re weld it shut. Could it cause other damage to the engine or what. no more than that car is driven I dont want to spend the bucks to replace the catany pros or cons please3Thanks Chuck Kerls Link to comment Share on other sites More sharing options...
NCReatta Posted June 18, 2011 Share Posted June 18, 2011 Problems I see are:Loss of some of the back pressure to the engine, making it not run quite as it should.And the fact that the cat (at least OEM) is stainless I believe, and requires a higher temp to weld back together. I was thinking of doing the same to my muffler, but the exhaust man I was talking to said that he wouldn't be able to weld it back. Link to comment Share on other sites More sharing options...
Guest spiering.lucas Posted June 18, 2011 Share Posted June 18, 2011 Get a new cat. The best thing you can do is fix it right not take short cuts. Buick spent thousands of dollars paying people to design this car to be perfect so don't mess with their work. You will loose gas mileage and some engine performance with no cat. You need the back pressure. Not to mention it will make your check engine light come one. The o2 sensor can't get an accurate reading without the cat and that is why everything i just told you above will happen. This is my knowledge from personal experience. Dont be cheap just buy a new cat. Link to comment Share on other sites More sharing options...
Guest steveskyhawk Posted June 18, 2011 Share Posted June 18, 2011 I would replace the cat. Air quality is important to me. Link to comment Share on other sites More sharing options...
Guest BAABUICK Posted June 18, 2011 Share Posted June 18, 2011 I replaced my cat with a straight pipe several years ago & haven't had any issues (no fumes, no rasp). If anything, the exhaust note is a little deeper. Link to comment Share on other sites More sharing options...
Guest BAABUICK Posted June 18, 2011 Share Posted June 18, 2011 Get a new cat. The best thing you can do is fix it right not take short cuts. Buick spent thousands of dollars paying people to design this car to be perfect so don't mess with their work. You will loose gas mileage and some engine performance with no cat. You need the back pressure. Not to mention it will make your check engine light come one. The o2 sensor can't get an accurate reading without the cat and that is why everything i just told you above will happen. This is my knowledge from personal experience. Dont be cheap just buy a new cat.Contrary to to the above, replacing your cat with a test/straight pipe will not compromise fuel economy or engine performance. Furthermore, the O2 sensor is located before the cat so you will not have any issues with codes. Link to comment Share on other sites More sharing options...
padgett Posted June 18, 2011 Share Posted June 18, 2011 OTOH the ECM map is calibrated assuming some back pressure. I suspect you might loose a mpg or two - nothing major, prolly about the same as underinflated tires. Link to comment Share on other sites More sharing options...
Guest spiering.lucas Posted June 18, 2011 Share Posted June 18, 2011 Dont be cheap just buy a new cat, its there for a reason. Link to comment Share on other sites More sharing options...
Booreatta Posted June 18, 2011 Author Share Posted June 18, 2011 Contrary to to the above, replacing your cat with a test/straight pipe will not compromise fuel economy or engine performance. Furthermore, the O2 sensor is located before the cat so you will not have any issues with codes. is it legal to just run a straight pipe?? Link to comment Share on other sites More sharing options...
NCReatta Posted June 18, 2011 Share Posted June 18, 2011 is it legal to just run a straight pipe??not in NC... but it helps to have friends in low places.. Link to comment Share on other sites More sharing options...
Guest blue72beetle Posted June 18, 2011 Share Posted June 18, 2011 Does Kansas inspect? If it was originally equipped with it, it must have it.Indiana doesn't inspect here though. Remove the cat, and no one would know, or care.FWIW, my Jeep has an 02 sensor downstream of the cat. Awhile back, all the honeycomb material in my cat broke down and clogged up the muffler, some of it even came out the tailpipe. Never threw a code the whole time. I installed another cat, but now it's breaking down too. Once it starts getting bad, I'm just going to gut it. Link to comment Share on other sites More sharing options...
Guest BAABUICK Posted June 18, 2011 Share Posted June 18, 2011 is it legal to just run a straight pipe??Depends where you live. Emission laws vary from province to province, state to state. Link to comment Share on other sites More sharing options...
Guest Richard D Posted June 18, 2011 Share Posted June 18, 2011 No testing in Florida. After a 10 year very expensive "experiment" the number of cars failing the test was so low the state canceled the program, sold the buildings for cents on the dollar or tore them down. Link to comment Share on other sites More sharing options...
handmedownreatta Posted June 19, 2011 Share Posted June 19, 2011 some cats have a heat shield that bolts on.be sure thats not whats rattling. Link to comment Share on other sites More sharing options...
Guest Recian Posted June 19, 2011 Share Posted June 19, 2011 I have yet to gut mine but im with BAABUICK on this one, The 02 is pre-cat and there's no after-cat sensor to monitor output hence no diagnostic logic that can detect a bad cat. However, i've seen some GM engines need the back pressure or they'll run like there's an intake leak, that's the only thing that's deterring me from doing this. All you gota do is take it loose from the clamp joint that's not even 6 inches behind the cat and punch it out from there. There's no need to cut unless that slip joint cant come off in which case you can cut it and get new slip on type adapters at the auto store and run new clamps to tie it all together. Just spray it down with some header 1500-2000 degree paint to prevent rusting of the adapters and hardware and boom. The whole system cant be stainless cuz mine is rusting so welding in a test pipe wouldnt be hard either. It's not legal to cut off your cat that's why muffler shops wont do it unless you know them well and most states you cant pass inspection but im a NC state inspector so that's not an issue to me Link to comment Share on other sites More sharing options...
KDirk Posted June 19, 2011 Share Posted June 19, 2011 Well,My 91 has no cat. It was removed prior to my ownership, and has a straight pipe very professionally installed (flared and welded). The car runs fine, fuel economy could be a bit better but I cannot necessarily attribute that to the lack of a cat converter. The car runs great, has no abnormal exhaust smell, and never throws any codes. As already covered here, the O2 is upstream of the cat, and is unaffected. Given the cost, I am disinterested in putting it back in since the car seems not to miss it. I rather doubt the pollution factor is much if any greater, since I keep the car in excellent running condition.As far as legality, technically it is supposed to have a cat. That said, Missouri no longer emission tests vehicles that predate the OBD2 standard, anything prior to the 1996 model year is thus exempt. Since an inspector never sees the car (for emissions, safety is still required, but they do not flag it on a safety check) it is below the radar, and thus has a defacto exemption. I'd bet it would pass even without the cat installed, but I'll never know since I don't have to do emissions tests on it. If you are in a jurisdiction that will not emissions test the car now or in the future, you could get by with a straight pipe. If you still have to get the "sniff test" then you will have to put a new one in to pass. Most places that still test pre-1996 cars not only test emissions but visually verify the presence of required factory emissions parts, the cat being the most obvious. KDirk Link to comment Share on other sites More sharing options...
handmedownreatta Posted June 19, 2011 Share Posted June 19, 2011 when the cat on my camaro was gutted the car got much louder. Link to comment Share on other sites More sharing options...
Guest Recian Posted June 19, 2011 Share Posted June 19, 2011 yeah in NC youre supposed to check for all factory emissions parts on even pre- 1996 but a gutted cat can still pass because all we're supposed to check is that it's there not that there's internals inside it Link to comment Share on other sites More sharing options...
padgett Posted June 19, 2011 Share Posted June 19, 2011 From 1975 to 1977 GM cats had a plug in the bottom. Unscrew the plug, pour out the pellets, and you had a nice muffler (could run a straight pipe out of it). For 1978 they sealed the plug. Link to comment Share on other sites More sharing options...
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