# how to tell if catalytic converter is bad?



## ahardb0dy (Nov 9, 2003)

3 questions: Is there any way to tell if the "cat" is going bad as far as being clogged?

2nd:, does anyone know of anyone that makes a test pipe for the B-12 sentra?

lastly what diameter is the exhaust pipe in front and rear of the "cat"


Thanks


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## nastynissan (Jan 26, 2003)

ahardb0dy said:


> 3 questions: Is there any way to tell if the "cat" is going bad as far as being clogged?
> 
> 2nd:, does anyone know of anyone that makes a test pipe for the B-12 sentra?
> 
> ...


1...... Yes there is a way to test. Drill/Torch a 1/2" hole in the exhaust before and after the Cat. Have someone Rev the engine while feeling the pressure coming out of the holes.

If there is a large difference in the 2 your Cat is getting clogged.

If theyre close to the same..... Figure out how to close the holes..... Welder

2....... There is NO reason for a test pipe. ALL that this will accomplish is further DESTROYING the atmosphere..... Properly operating Cats have little to NO effect on performance. In the Early 80's yeah they were a problem. NOT now.

3.......... F&R exhaust size is 1 3/4" (I think).


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## ahardb0dy (Nov 9, 2003)

thanks for the reply, I know the cat's aren't very restrictive, not that it would matter any on my stock engine, I was just curious, I was wondering if the cat possibly getting clogged may have had something to do with the hose going from the AIV to the exhaust manifold blowing out. Replaced the hose tonight with a used one for now until the new one comes in, guess I'll have to just see if anything happens to the new/used hose, don't think anything will.


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## dreamteam (Jul 29, 2005)

You can run a vacuum guage tester to check the cat.

Needle will bounce on idle.

As the engine is accelerated the needle will drop.


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## bob89sentra (Sep 15, 2005)

Yup like dreamteam said hook a vacuume gauge to the intake, and see what it does. If you have a chiltons manual there is a section that covers what varius vacuume readings mean, works as a great diagnostic tool.


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## Biscuit (Mar 5, 2005)

Making a test pipe will make things louder...that is about it. I also heard that taking off your cat lowers your gas mileage...which I think is false. If I wanted to find out if my CAT was constipated then I would take it to Midas and let them check it for free or something.


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