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Old 03-01-2012, 09:39 PM   #1
ManualOverAuto
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Ok, I was told by a pretty trustworthy mechanic that my cat is bad. I know that's not very legible even if the mechanic is the most knowledgeable one out there.

With that being said I have a feeling it could be a possibility. And here's why:
-CEL p0420 for the last 4 months or so
-20 MPG (2.2L, manual) should be like 25-30
-my exhaust has that leaking sound to it but no exhaust leaks
-rotten egg smell a few times

How can you tell if a cat is bad?

I'd rather my CEL be for sensors than a cat. If its the cat I have to pay $800 for a new one to pass inspection in 6 months.
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Last edited by ManualOverAuto; 03-01-2012 at 11:29 PM.
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Old 03-02-2012, 10:18 AM   #2
DaWhiteScoob
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I'm pretty sure you have a clogged cat... the "rotten egg smell" gives it away also the P0240 cel.

You could have the cel code disabled to save a lot of money.
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Old 03-02-2012, 12:46 PM   #3
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Quote:
Originally Posted by DaWhiteScoob
I'm pretty sure you have a clogged cat... the "rotten egg smell" gives it away also the P0240 cel.

You could have the cel code disabled to save a lot of money.
Yea I cleared the code like last week. Still need to get a new cat eventually cause the gas mileage kills me. And it probably won't pass emissions :/

Last edited by ManualOverAuto; 03-02-2012 at 01:56 PM.
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Old 03-02-2012, 10:03 PM   #4
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Odds are it's your cat, probably part of it has broken inside the pipe and it's clogging your exhaust up - causing the noise you're hearing. Crawl under it when it's cooled off and bonk the pipe with your hand and see if it sounds like crap rattling around in there.

If so, the best short-term fix is to unbolt it and mash the guts up and dump them out. You'll still have a CEL, but you're going to get better fuel economy by removing the restriction and it will lessen the likelihood of creating other problems. Save your dimes for a few months and get yourself a new cat. You may need to save enough for new sensors, as they may be the reason the cat went bad to begin with, or they may not come out of the old pipe in one piece.
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Old 03-03-2012, 01:26 AM   #5
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Quote:
Originally Posted by CosmoTheCat
Odds are it's your cat, probably part of it has broken inside the pipe and it's clogging your exhaust up - causing the noise you're hearing. Crawl under it when it's cooled off and bonk the pipe with your hand and see if it sounds like crap rattling around in there.

If so, the best short-term fix is to unbolt it and mash the guts up and dump them out. You'll still have a CEL, but you're going to get better fuel economy by removing the restriction and it will lessen the likelihood of creating other problems. Save your dimes for a few months and get yourself a new cat. You may need to save enough for new sensors, as they may be the reason the cat went bad to begin with, or they may not come out of the old pipe in one piece.
As right as you sound, I really hope your wrong lol :/ ($800)

But I've known about it so it's no surprise, just hasn't been completely confirmed yet. Hoping it could just be a bad sensor causing it all. But before I buy new sensors I'll get under and see if I hear any rattle from the cat. Just gotta wait till its dry and not cold here.......
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Old 03-03-2012, 01:35 AM   #6
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Who pays 800$ for a cat dude? Get a used one and toss it in. 800 is madness
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Old 03-03-2012, 02:05 AM   #7
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Sounds like your cat is done! what kind of mileage do you have?

9 times out of 10, P0420 = bad cat.

Buyer beware when buying a used cat. It's way way way cheaper but there's a chance there could be something wrong with it too, from my personal experience.
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Old 03-03-2012, 02:05 AM   #8
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Yeah it is, subaru said it would have been $1000 to replace the one in the headers on mine when it went bad, luckily it was under 80k mile catalyst warranty

Id say 9/10 sounds something close, I have the 1/10 with different headers though haha
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Old 03-03-2012, 08:53 AM   #9
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Quote:
Originally Posted by lavid2002 View Post
Who pays 800$ for a cat dude? Get a used one and toss it in. 800 is madness
where?

when i asked at the local junk yard, i was told that they cannot sell any used cats unless they want to pay a $10000 fine for each occurance.

something about the EPA not knowing it would be installed on the system it was designed for.

private sale might be doable, not sure if that would be illegal or not.

point being if anyone out here has a known good cat for a '00 OBS with a 2.2....PM me

rumor has it that only subaru cats will work well on subarus...i also hear they are in the $7-800 range, ive been afraid to call for a price.
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Old 03-03-2012, 09:07 AM   #10
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its seems crazy high.

I did a quick google search and found this OEM replacement for under $250

http://www.autopartswarehouse.com/sh...u/outback.html

It seems like people are always giving away used exhausts too... usually because they've replaced them with aftermarket so there's nothing wrong- but you have a good point, no sense replacing one bad cat with another
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Old 03-03-2012, 11:58 AM   #11
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^^ that's probably your best bet, walker exhausts might have something better too, I got an oem 05' cat pipe for an rs a while ago at it was only $270 I think (there's two cats on the 05 that I bought)
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Old 03-03-2012, 12:06 PM   #12
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Quote:
Originally Posted by lavid2002
Who pays 800$ for a cat dude? Get a used one and toss it in. 800 is madness
That was for parts and labor. But I'm sure I could find a cheaper oem replacement but labor is still gonna be there.
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Old 03-05-2012, 04:45 PM   #13
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Sometimes the P0420 can be the front O2 sensor... but given the smell and gas mileage, I'd say it's the cat too. Mine was ~$600 for our Forester, new and installed.
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Old 03-05-2012, 10:13 PM   #14
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P0420 could be a vacuum leak.

But most often it's a bad cat.
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Old 03-06-2012, 01:25 AM   #15
ManualOverAuto
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Thanks for all the replies. If the cat is bad then it's bad, nothing I can do about it.

I would like to specify that by smelling the rotten egg smell I mean I've smelled it maybe 3 or 4 times max. Not very common but has happened. Although since its been winter I haven't smelled it once (odd?). Either way in 6 months when inspection is due I'll need a new one anyway.
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Old 03-06-2012, 04:49 AM   #16
Robert Harik
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You can test to see if you have a exhaust / cat restriction by hooking up a vacuum gauge to your intake manifold. Once you start the car, let it idle , if you have a restriction your vacuum will start out normal( 18- 22 ( Hg) inches of mercury) and then slowly drop( vacuum will get less).

Last edited by Robert Harik; 03-06-2012 at 05:07 AM.
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Old 03-06-2012, 11:03 AM   #17
ManualOverAuto
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Quote:
Originally Posted by Robert Harik
You can test to see if you have a exhaust / cat restriction by hooking up a vacuum gauge to your intake manifold. Once you start the car, let it idle , if you have a restriction your vacuum will start out normal( 18- 22 ( Hg) inches of mercury) and then slowly drop( vacuum will get less).
Ok might try this. Will any vacuum gage work?
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Old 03-06-2012, 12:35 PM   #18
Matt Monson
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Quote:
Originally Posted by jeepnut_nh View Post
where?

when i asked at the local junk yard, i was told that they cannot sell any used cats unless they want to pay a $10000 fine for each occurance.

something about the EPA not knowing it would be installed on the system it was designed for.

private sale might be doable, not sure if that would be illegal or not.

point being if anyone out here has a known good cat for a '00 OBS with a 2.2....PM me

rumor has it that only subaru cats will work well on subarus...i also hear they are in the $7-800 range, ive been afraid to call for a price.
Post a WTB in your local regional forum here on NASIOC. That's what local forums are for. I'm sure there's a couple of people out there who have installed headers and a high flow cat and have a stock one just sitting gathering dust.

Not that it helps you, but I've got 4 or 5 stock WRX downpipes out in my shed. There's guys like me all over the country. I'm not unique. You just need to put your request in front of the right eyes. And don't worry about what you are doing being illegal. It is illegal for a business to sell used catalyst parts, but you are at no risk with a private party sale.
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Old 03-06-2012, 12:40 PM   #19
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Quote:
Originally Posted by Matt Monson View Post
Post a WTB in your local regional forum here on NASIOC. That's what local forums are for. I'm sure there's a couple of people out there who have installed headers and a high flow cat and have a stock one just sitting gathering dust.

Not that it helps you, but I've got 4 or 5 stock WRX downpipes out in my shed. There's guys like me all over the country. I'm not unique. You just need to put your request in front of the right eyes. And don't worry about what you are doing being illegal. It is illegal for a business to sell used catalyst parts, but you are at no risk with a private party sale.
thanks for the info matt, i will do that once i find work and get back on my feet
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Old 03-06-2012, 03:42 PM   #20
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Quote:
Originally Posted by ManualOverAuto View Post
Ok might try this. Will any vacuum gage work?
Any one that is accurate and within the right range( at least 0 -25 Hg. They make ones for auto use that are really useful for all kinds of testing.
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Old 03-06-2012, 06:18 PM   #21
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Quote:
Originally Posted by Robert Harik

Any one that is accurate and within the right range( at least 0 -25 Hg. They make ones for auto use that are really useful for all kinds of testing.
So if the cat is clogged where do I go from there? There has to be an underlying cause to why it's getting clogged. I just hope it's not a head gasket burning oil and clogging it up. I did recently see that my coolant was a lot lower than usual, but I never smell burning coolant or oil. My oil is usually always at the same level when I check it too.

Hopefully it's just old and needs replacement. Or even better, my cat could be fine and it's just an o2 sensor, that'd be greeeaaattt.
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Old 03-06-2012, 08:53 PM   #22
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Your right, cats die from contamination( usually oil , coolant),but can also be destroyed by overheating( monolith( inside) melts/ falls apart). Its caused by raw fuel reaching and burning inside the cat. It can be caused by very rich running( bad sensors) , missing( every time a cylinder misses unburned fuel is passed into the cat).If you still have the problem that melted( if that is the your problem) the cat in the first place , it will eventually ruin your new cat.
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Old 03-06-2012, 10:04 PM   #23
ManualOverAuto
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Quote:
Originally Posted by Robert Harik
Your right, cats die from contamination( usually oil , coolant),but can also be destroyed by overheating( monolith( inside) melts/ falls apart). Its caused by raw fuel reaching and burning inside the cat. It can be caused by very rich running( bad sensors) , missing( every time a cylinder misses unburned fuel is passed into the cat).If you still have the problem that melted( if that is the your problem) the cat in the first place , it will eventually ruin your new cat.
Can you tell more specifically when looking at the old cat what could have cause it to go bad? Like what residues are around/on the inside of the cat? If so I'll have them check it if I get a new one.

I don't believe I'm burning oil but my coolant seems to always go down to like 1/2-3/4 of the way full after its topped off, so maybe I'm burning coolant.

Another possibility could be that maybe it's the original cat. I know my exhaust pipes underneath are newer than the car but I've heard that you don't always replace the cat when you get new pipes. Makes sense because if the cat isn't bad it'll save $800+ on that new exhaust. Car has almost 110k and 11-12 years on it so who knows.
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Old 03-06-2012, 11:33 PM   #24
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First find out if it is bad, then diagnose. Like I said ,usually a dead cat( not the road pizza type) is caused by oil or coolant contamination and these are not usually blocked/ clogged up. If it is melted or the substrate has fallen apart, it is from overheating and that is caused by large amounts unburned fuel getting into the cat. Thats it.
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Old 03-06-2012, 11:50 PM   #25
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Quote:
Originally Posted by Robert Harik View Post
First find out if it is bad, then diagnose. Like I said ,usually a dead cat( not the road pizza type) is caused by oil or coolant contamination and these are not usually blocked/ clogged up. If it is melted or the substrate has fallen apart, it is from overheating and that is caused by large amounts unburned fuel getting into the cat. Thats it.
Are those things are the ONLY things that can cause a cat to go bad?

What if i told you my exhaust from the cat on up are all original (110k, 11-12 years on car, 3 owners), and everything else after the cat was replaced at one point.

Dont you think small amounts of unburned fuel / burned oil / burned coolant over a longer time (11-12 years) could do the same damage?

Alot of oil/coolant/unburned gas over a shorter time. = Small amounts of oil/coolant/unburned gas over a long time.
Right?
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