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Old 08-22-2010, 12:45 AM   #1
rhauf
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How can you tell if your catalytic converter is bad?

Does anyone know if its possible to tell a bad cat from a good one?

i have my exhaust cut apart and they look fine inside.. (normal honey comb looking stuff, not falling out, rotted or clogged) so i'm wondering if they are good or bad?

reason i suspect them, is because it barely passed smog last time (year ago) and the smog tech thought it was the cats going bad. but they look fine.

can they be worn out and still "look" good?
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Old 08-22-2010, 08:59 AM   #2
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The only true way to test a converter that appears fine physically is with an o2 sensor before and after cat.The primary job of the cat is to convert the harmful emissions from the engine to a cleaner exhaust out the tail pipe.The ability of the cat to "light off" and store and release oxygen does deteriorate over time.The only way to check its ability to do so is with a second o2 after the cat or a tailpipe test.If you are certain the engine is mechanically running correct but the emissions reading is high there is a good possibility the cat is going bad.In older vehicles without the second o2 to trip the dreaded 420,421,430,or 431 codes (cat efficiency codes)a good indicator is an elevated NOX reading.
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Old 08-22-2010, 02:04 PM   #3
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Your rig will also give symptoms if the cat is clogged. You can jump on the gas and your rig will bogg down, you will not be able to go over a certain speed. Also the cat will get extremely hot after running the rig.
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Old 08-23-2010, 12:02 AM   #4
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yeah your exhaust will get very very hot and you'll most likely have lack of power problems when going more than 75 % throttle. pending on if its clogged. On some the element will break and rattle inside them even. Also when a cat goes bad you can most of the time smell them. Id say cut it out and replace with a straight pipe and pop in a few 02 simulators. but thats just me haha. Im not sure if the element can just wear out though in your case.
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Old 08-23-2010, 12:57 AM   #5
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i think my cats either clogged or bad, it seemed really hot last time i was under there and i only drove it like 2-5 minutes. also it doesnt liek to rev, higher rpm power isnt good.
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Old 08-23-2010, 10:03 PM   #6
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hi guys I'm new here just got my 93 bronco from crigslist i was happy to find this site after buying it...ok down to the ? its got 220k on the original motor and the exhaust looks bad, motor starts good and runs good for being that old but feels sluggish ..so the cat has this tube coming out from it an heading back up toards the motor its steel and rusted off or broke some how,
this set up is new to me so i don't under stand why its there or how bad it is to have it broke off the cat must be leaking ...im thinking of just replacing the whole exaust from the heads back ..does a cat get clogged up after 220k miles? thanks i know I'm all over the place
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Old 08-24-2010, 08:08 AM   #7
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Originally Posted by garys b.b.b. View Post
hi guys I'm new here just got my 93 bronco from crigslist i was happy to find this site after buying it...ok down to the ? its got 220k on the original motor and the exhaust looks bad, motor starts good and runs good for being that old but feels sluggish ..so the cat has this tube coming out from it an heading back up toards the motor its steel and rusted off or broke some how,
this set up is new to me so i don't under stand why its there or how bad it is to have it broke off the cat must be leaking ...im thinking of just replacing the whole exaust from the heads back ..does a cat get clogged up after 220k miles? thanks i know I'm all over the place
220k is a lot for an original cat! And that tube is your EGR Tube
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Old 08-24-2010, 12:53 PM   #8
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220k is a lot for an original cat! And that tube is your EGR Tube
the egr tube takes exhaust from the manifold on the engine. what hes talking about is the AIR tube for the smog. if thats not working the cat prolly wont get up to temperature and itll clog.
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Old 08-24-2010, 01:04 PM   #9
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your cats will turn red hot like a cigarette lighter, and most often times you'll smell a rotten egg smell from the car behind you. Lack of power is another big sign. Its pretty hard to tell if they're bad unless they get totally clogged, or unless you have an 02 sensor. I always recommend replacing them before you need too. every 65-100k miles is a good marker. My dad owned a 78 caprice (beautiful car, it was pristine) and my mom took it over to philly to pick up hard to find presents for my little sister in 2002. Cat was clogged and the car ended up lighting on fire on the bridge, and my mom didn't even know it. someone ended up pulling in front of her and stopping. As soon as she got out, she said the seat lit on fire.

So just a little story for you guys. I know its rare, but just something to think about ya know...
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Old 08-24-2010, 01:08 PM   #10
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your cats will turn red hot like a cigarette lighter, and most often times you'll smell a rotten egg smell from the car behind you. Lack of power is another big sign. Its pretty hard to tell if they're bad unless they get totally clogged, or unless you have an 02 sensor. I always recommend replacing them before you need too. every 65-100k miles is a good marker. My dad owned a 78 caprice (beautiful car, it was pristine) and my mom took it over to philly to pick up hard to find presents for my little sister in 2002. Cat was clogged and the car ended up lighting on fire on the bridge, and my mom didn't even know it. someone ended up pulling in front of her and stopping. As soon as she got out, she said the seat lit on fire.

So just a little story for you guys. I know its rare, but just something to think about ya know...
sounds a but frequent dont ya think?
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Old 08-24-2010, 01:18 PM   #11
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sounds a but frequent dont ya think?
maybe. I mean I usually do it every 100k. My dad had a pretty new exhaust system on the car when it burnt up, so its always been a scary thought in my head. Plus my exhaust system gets changed often on my vehicles. Maybe I exaggerated a bit at 65 that'd be ridiculous, but again, that thought of the car burning up will stay with me forever. She said had she gotten out of the car 30 seconds later she would have been burnt badly. I'll see if i can find the pictures my mom took of it on fire.
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Old 08-24-2010, 01:23 PM   #12
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My 88' would bog down, backfire, and idle rough and be really hard to get up to speed even when mashing the gas pedal to the floor, cut both cats off(Cali truck) and now it Idles and gets up to speed just fine.
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Old 08-24-2010, 01:26 PM   #13
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i wonder if hi flow cats last longer.
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Old 08-24-2010, 01:56 PM   #14
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I got a question because i think mine is bad. (High speeds theres noo power)
Im worried i replace the one closest to the rear, and nothing happens because its the one in the y pipe itself. Is it common that the y pipe clogs or should i be good with replacing the one closest to the rear?
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Old 08-24-2010, 01:56 PM   #15
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Old 08-24-2010, 10:11 PM   #16
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Originally Posted by pfun41 View Post
the egr tube takes exhaust from the manifold on the engine. what hes talking about is the AIR tube for the smog. if thats not working the cat prolly wont get up to temperature and itll clog.
Quote:
Originally Posted by Smok3y View Post
your cats will turn red hot like a cigarette lighter, and most often times you'll smell a rotten egg smell from the car behind you. Lack of power is another big sign. Its pretty hard to tell if they're bad unless they get totally clogged, or unless you have an 02 sensor. I always recommend replacing them before you need too. every 65-100k miles is a good marker. My dad owned a 78 caprice (beautiful car, it was pristine) and my mom took it over to philly to pick up hard to find presents for my little sister in 2002. Cat was clogged and the car ended up lighting on fire on the bridge, and my mom didn't even know it. someone ended up pulling in front of her and stopping. As soon as she got out, she said the seat lit on fire.

So just a little story for you guys. I know its rare, but just something to think about ya know...
thanks ill check to see if it gets red for sure! about that tube it flows air back to the heads ?just asking so when i fix it im sure the aouther end that it connects to is just as bad. so you would u say i should just plan on replacing it since that tube is toast? ive seen this magnaflow high flow cat direct fit for like 200 bucks any addvice or better choice out there ?
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Old 08-24-2010, 11:07 PM   #17
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thanks ill check to see if it gets red for sure! about that tube it flows air back to the heads ?just asking so when i fix it im sure the aouther end that it connects to is just as bad. so you would u say i should just plan on replacing it since that tube is toast? ive seen this magnaflow high flow cat direct fit for like 200 bucks any addvice or better choice out there ?
think of it this way, the farther the trub gets from the exhaust the less heat and corrosive elements it experiences, so the less damage it will see.any decent metal pipe will work though and you can use high temp tubing to splice it in.
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