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Old 01-23-2007, 05:39 PM   #1
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Stock exhaust/cat question

Just had a cat replaced (under factory 7/70,000 mile warranty, thank god!!) and after seeing what the replacement would have cost me ($1100)!! I started to wonder...

1)Why do we have 4 cats?

2)When 1 goes bad can I expect another to follow in short order (kinda like the O2 Sensors going bad)?

3)The Porsche mechanic says they will only last 60-70,000 miles on most Imported autos due to the computer monitoring the exhaust flows very closely to pass U.S emissions. He says domestics do not have to monitor the exhaust flow as closely because of relaxed standards for U.S. made autos?!?!?! He says this is why most US cars Cats will literaly fall/rot off rather than set a code for reduced performance?!?!?!?!

Food for thought---$1000 per cat at the stealership @4 cats= $4000! Not something to look forward to...
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Old 01-23-2007, 05:55 PM   #2
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Should my cats rust away they'll be replaced with 100 cell aftermarket cats for sure. That replacement price is simply outrageous.
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Old 01-23-2007, 08:06 PM   #3
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Originally Posted by RandallNeighbour
Should my cats rust away they'll be replaced with 100 cell aftermarket cats for sure. That replacement price is simply outrageous.
If I actually had to pick up the costs of replacing these I would probably bypass them or do as you describe above.
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Old 01-23-2007, 08:41 PM   #4
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Quote:
Originally Posted by xclusivecar
Just had a cat replaced (under factory 7/70,000 mile warranty, thank god!!) and after seeing what the replacement would have cost me ($1100)!! I started to wonder...

1)Why do we have 4 cats?

2)When 1 goes bad can I expect another to follow in short order (kinda like the O2 Sensors going bad)?

3)The Porsche mechanic says they will only last 60-70,000 miles on most Imported autos due to the computer monitoring the exhaust flows very closely to pass U.S emissions. He says domestics do not have to monitor the exhaust flow as closely because of relaxed standards for U.S. made autos?!?!?! He says this is why most US cars Cats will literaly fall/rot off rather than set a code for reduced performance?!?!?!?!

Food for thought---$1000 per cat at the stealership @4 cats= $4000! Not something to look forward to...
A catalytic converter can theoretically last forever. There is nothing in the converter that is consumed in it's operation.

In reality, burned oil, sulfer and other impurities can coat the catalyst and hinder it's ability to do it's job, thus wearing it out. Excessive heat and vibration can also damage the materials that support the catalyst material.

This is why a malfunctioning O2 sensor or MAF can damage the cat. It can throw off the required mixture for the catalyst and will usually cause damage through overheating (too much O2 in the mixture) or coating with materials that keep it from doing it's job (too much HC and other rich combustion byproducts).

In general, though, a healthy car with an engine kept in good working condition should have a catalytic converter that lasts at least as long as the engine.

The mechanic is dead wrong. OBDII forces the use of upstream and downstream O2 sensors on all cars. There's no reason in general for an American car to have a longer lasting cat than a German one.

Cats work best at the normal operational (hot engine) temperature. There are 2 close to the exhaust manifold so that they'll be brought up to operational temperature quickly. There are 4 total cats to expose as much gas as possible to the catalyst material to maximize the amount of gas that's treated.

High quality cats can be had for about $200 each. There's no need to use the Porsche parts.

Last edited by blue2000s; 01-24-2007 at 07:00 AM.
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Old 01-24-2007, 03:32 PM   #5
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50 miles after having my cat replaced and now another code...P1275 and P0133...more O2 codes. I had all 4 replaced in the last year and now here we go again!!!! It seems as if when one piece goes everything else follows!
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Old 01-24-2007, 07:45 PM   #6
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xclusivecar,

What dealer or shop do you use? PM if you don't want to post here.
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Old 01-24-2007, 09:15 PM   #7
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Quote:
Originally Posted by xclusivecar
50 miles after having my cat replaced and now another code...P1275 and P0133...more O2 codes. I had all 4 replaced in the last year and now here we go again!!!! It seems as if when one piece goes everything else follows!
Have they tried the MAF?
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Old 01-24-2007, 09:39 PM   #8
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Hi,

Initial Mis-Diagnosis. The Codes have to be interpreted. There is no code - "Your CAT is going Bad, or has failed", the DME will state any number of irregular operations and it's up to the Mechanic to make the proper interpretation. Unfortunately, these guys usually go with what they see most often, or what is the most expedient. Good Luck!...

Happy Motoring!... Jim'99
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Old 01-25-2007, 06:33 AM   #9
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Quote:
Originally Posted by shaman1204
xclusivecar,

What dealer or shop do you use? PM if you don't want to post here.
Different shops since I bought this car 3 years ago due to a move,warranty considerations, and other variables. I have yet to settle on one specific shop although I should. To date have used MotorWerks Barrington, Luxury Motors Schaumburg, Luxury Motors Chicago, Fox Valley Motorsports in West Chicago, and probably a few others. All have been decent experiences...but these damn emission codes are killing me!!!!!
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Old 01-25-2007, 06:39 AM   #10
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Quote:
Originally Posted by MNBoxster
Hi,

Initial Mis-Diagnosis. The Codes have to be interpreted. There is no code - "Your CAT is going Bad, or has failed", the DME will state any number of irregular operations and it's up to the Mechanic to make the proper interpretation. Unfortunately, these guys usually go with what they see most often, or what is the most expedient. Good Luck!...

Happy Motoring!... Jim'99
You are right when it came time to replace the MAF and O2 sensors...every mechanic just glanced at the codes and replaced something...and then a new code would pop up just miles later...back in I went. I have gone a year without codes until this last one. The CAT code. The Porsche mechanic used his diagnosis equipment and stated the flow rates for the cat was low thus replacing it. He also advised that one of my O2 sensors was bad (although I had it replaced in the last 3 months). Hmmmm...now that I'm typing this I realize I am just repeating what happened a year ago...replace parts until its fixed...not very efficient!
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