# What are the symptoms of a clogged cat?



## groggory (Apr 21, 2003)

As title...


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## AmIdYfReAk (Nov 8, 2006)

Lack of Exhaust flow out the back, Turbo and manni getting excessively hot, no power, RPMS will not climb or will do so slowly. 

Easy way to test, use a temp probe before and after the cat, they should be around the same temp.


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## Cryser (Sep 9, 2009)

loss of acceleration especially in a turbocharged engine. 

Rotten egg smell 

Blown downpipe gasket or in my case it actually blew the weld on my ebay downpipe instead of the gasket(this leads me to believe the gasket was actually stronger then the weld :what: ) 

muffled exhaust note. 

There was a post about this and I posted a link to a simple easy test you can do with a vacuum gauge. Seeing as most 1.8T owner who mod have a vacuum/boost gauge in there car you can do most of those tests without even getting any tools out. 

I *believe* your gonna have a lower vacuum then normal at idle and when you bring the revs to 2000rpm standing still the needle with begin to bounce or shake between 15-10 inHg in cases of extreme blockage... causes of little or partial blockage will note an overall lower reading then normal. I have to double check that though in my auto books to be sure though, when I find it I'll confirm or change it


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## MarkusWolf (Dec 10, 2001)

groggory said:


> As title...


 

Someone told me to hold the the cat (while it is off) to the light and if you cannot see through it, then it is clogged. 

May be Seafoam to get "some" carbon out?


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## groggory (Apr 21, 2003)

My car seems much louder at deceleration

Lots of power loss

Sometimes misfires at idle, throttle blip fixes it


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## Cryser (Sep 9, 2009)

MarkusWolf said:


> Someone told me to hold the the cat (while it is off) to the light and if you cannot see through it, then it is clogged.
> 
> May be Seafoam to get "some" carbon out?


 
you can do this is you don't have a weld in cat, yes you should be able to see through an unclogged cat easily with a flash light. 

The problem with clogged cats is that the substrate of the cat is usually melted and become soild, seafoam won't fix this problem nor would it make it to your cat to clean it out. Although if you did seafoam and saw little to no smoke on the initial start up and it's been more then 50 miles since you seafoamed that could indicate a clogged cat. 

The most common cause of a clogged cat in a performance tuned car is when the car runs too rich. Excess fuel is dumped into the car, The fuel gets caught in the substrate, as the car heats up(say a WOT run) the deposited fuel in the cat explodes breaking the substrate and then instantly welding it back together into a solid mass. For those that don't know, inside your cat is a honeycomb that is coated with precious metals. Constant explosions inside your cat from running excessively rich(10.5 or lower) causes this honeycomb to breakdown and become a solid mass. If you can a straight through exhaust or one with minimal bends you can actually grenade this solid substrate out the exhaust if it is broken free from the inside walls of the cat. If you have been running excessively rich for a while and notice the symptoms stated above by grogg your cat being clogged is a high possibility. 

Grogg your gonna wanna get a vacuum gauge that can thread into an 02 sensor bung, read the vacuum pulled before and after the cat, if there is a vast difference,(post cat being much lower) you cat is clogged and needs to be removed/replaced. 

If you can get your car on a lift and you tap on the cat after it cools down and it sounds and feels solid all the way through it may be clogged, it should sound and feel a tad hollow. *Warning* if you cat is breaking up inside and you hit it too hard you maybe accelerate the process and break the honeycomb on the inside, lightly tap if you chose to test this way


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## Chickenman35 (Jul 28, 2006)

Here is an excellent article on the design and operation of modern catalytic converters: 

http://www.aa1car.com/library/converter.htm 

One other symptom not mentioned, is that sometimes you will get a rattle under acceleration that sounds like a bunch of marbles in a tin can. This can be quite loud. It is sometimes mistaken for pre-ignition, but is much louder, and usually does not trigger the knock sensors. 

This " loud rattle " is caused by advanced degradation of the catalytic convertor and is bits and pieces of the broken and melted honeycomb substrate that is bouncing around inside the converter shell. 

Pulling the cat and visually examining it will reveal the damage.


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## groggory (Apr 21, 2003)

New cat for me. Those are my symptoms.

Can someone link me to a recommended cat for a 3" exhaust?

Preferably one that has two o2 bungs pre-cat and one bung post cat?

Ps... What would it take to modify my exhaust so I have essentially a v-banded dump tube?


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## hatetolovemydub (Oct 27, 2009)

42 dd 3" dp and race cat, Ftmfw. Super high quality, $300.... Can't go wrong, although some will say buy an Ebay one, I disagree. :thumbup:


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## Chickenman35 (Jul 28, 2006)

Dynomax, Walker, Magnaflow, Random Technologies all make Universal 3" High Flow Cats from $170 to $200. Add your own bungs and V-band it. 

http://www.jegs.com/i/Magnaflow/642/59959/10002/-1?parentProductId=763223#moreDetails 

Edit: Uh oh...you live in a Police State ( California ). New laws in CA from 2009. A lot of companies will no longer ship universal cats to California. 

But you will be picking it up directly from a local Speed shop right? And it's going on your " Race car " that never sees public roads... right? Lots of race series now require Catalytic converters. Nudge, nudge, wink wink. 

Or a nice vacation to Vegas might be just what you need. I here that Summits main warehouse is in Vegas. Would be nice to see. I bet they carry all sorts of Universal " Parts " for "Race Cars". Carry cash, lots of cash.... ( Cash good...Credit cards and Debit cards bad )


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## groggory (Apr 21, 2003)

hatetolovemydub said:


> 42 dd 3" dp and race cat, Ftmfw. Super high quality, $300.... Can't go wrong, although some will say buy an Ebay one, I disagree. :thumbup:


 Got it

42dd, plus
Wideband bung
Egt bung
Race cat
Ceramic coat
3" resonated
Single tip, double wall


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## Twopnt016v (Jul 5, 2009)

The best to test for a clogged cat is with a back pressure tester. You remove the o2 sensor and install gauge. Checking temps before and after the cat is not really a good way to test....


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## groggory (Apr 21, 2003)

Twopnt016v said:


> The best to test for a clogged cat is with a back pressure tester. You remove the o2 sensor and install gauge. Checking temps before and after the cat is not really a good way to test....


 What is the backpressure of a healthy 1.8t and what is the backpressure of an unhealthy 1.8t? 

Do you do this backpressure measurement at idle, at xxxx RPM @ no load, or at yyyy RPM @ load?


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## Chickenman35 (Jul 28, 2006)

groggory said:


> What is the backpressure of a healthy 1.8t and what is the backpressure of an unhealthy 1.8t?
> 
> Do you do this backpressure measurement at idle, at xxxx RPM @ no load, or at yyyy RPM @ load?


 Link in my post #7 has all the info you need on measuring back pressure. 

http://www.aa1car.com/library/converter.htm


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## groggory (Apr 21, 2003)

Chickenman35 said:


> Link in my post #7 has all the info you need on measuring back pressure.
> 
> http://www.aa1car.com/library/converter.htm


 Awesome. Added it to my FAQ


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## BMP20th (Jul 23, 2006)

you can also check the oil cap and the pcv stuff. we had a car in the shop the other day with a clogged cat. it had some serious crank case pressure and was spewing oil around the cap.


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## groggory (Apr 21, 2003)

BMP20th said:


> you can also check the oil cap and the pcv stuff. we had a car in the shop the other day with a clogged cat. it had some serious crank case pressure and was spewing oil around the cap.


 If I open my oil cap it is puffing out a pretty hefty amount of gassy fumes


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## MarkusWolf (Dec 10, 2001)

BMP20th said:


> you can also check the oil cap and the pcv stuff. we had a car in the shop the other day with a clogged cat. it had some serious crank case pressure and was spewing oil around the cap.


 Mine does that:


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## xxsur3shotxx (Sep 24, 2009)

groggory said:


> If I open my oil cap it is puffing out a pretty hefty amount of gassy fumes


 I think it's normal for the cap to "dance" on the valve cover if you open it and let it sit. 

Anyway, how is your manifold vacuum at idle? Notice any decrease in vacuum? When you have a clogged cat, you will often see a decrease in vacuum.


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## groggory (Apr 21, 2003)

xxsur3shotxx said:


> I think it's normal for the cap to "dance" on the valve cover if you open it and let it sit.
> 
> Anyway, how is your manifold vacuum at idle? Notice any decrease in vacuum? When you have a clogged cat, you will often see a decrease in vacuum.


 Sometimes it drops to around 10... But if I blip the throttle it'll go to 18 or 20. If it's behaving it'll be 20.

Back when the car was running right it was idling at 22.


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