[A4] How much for a catalytic converter for my A4?
brian at atomicham.com
Wed Jan 23 09:38:24 PST 2008
> I have never had to replace a converter in any of my cars (VW Golf --
> 290,000 km, 1988 Audi 90 -- 287,000 km, 1990 Audi 90, 310,000 km, Audi
> A4 -- 160,000 km, and a couple of Subarus that have gone over 250,000
> km). Granted much (~70%) of my driving is highway.
But, you don't know where she lives. In places like Colorado where the
temps go from sub-zero to 60+F in a day, catalytic converters can
crumble regularly (especially if the car lives outside). I had to
replace them on two Audis (both V6s, which each have two cats).
Remember that internally cats are made of a ceramic mesh covered in
platinum (or palladium or rhodium), and can be quite brittle. That
said, unless you live in an environment that can go from cold to hot
quickly, it shouldn't break unless there are other problems (you can
destroy a cat by sending a lot of unburned fuel out of the exhaust,
but your car would throw codes and run terribly if that happened).
> A bad converter will either be plugged up or blown apart. If it is
> blown apart power loss will not be a problem and it will be LOUD. If
> it is plugged up it will be consistent in terms of poor power.
Secondly, you are incorrect that a blown cat is loud. It won't make
any difference in noise. Catalytic converters are for emissions only.
What you will hear with a blown cat is a sort of popcorn type of sound
with the windows down as you cruise at a relatively low speed. What
you are hearing are the pieces of ceramic bouncing inside of the
stainless steel container. An easy (but not certain) test to see if
yours is bad is to crawl underneath and knock on the cat. If you hear
pieces rattle around inside, it is shot.
So, what is the end result of all of this? Well, you can choose to
leave it as is, or you can replace it. From Audi, they cost in the $1k
range. I'm sure this is where your mechanic got the quote for the
part. I bet the wholesale list price from Audi is around $700. If you
buy a generic aftermarket, you'll need someone to cut the existing
pipe and weld the new one in, just make sure they don't muck up the
post-cat O2 sensor plug.
Short from taking it off of the car, you have no quantifiable way of
really knowing it is shot.
As for your O2 sensors, you really should change them around 90k. O2
sensors can continue to give readings that don't trigger CEL codes;
however, their response becomes extremely poor. You can hook them to
an oscilloscope and vary the throttle. You should see a nearly
immediate and sharp signal. Usually (around 90k is a guideline) when
they are no longer as responsive, it will be a very gradual curve as
the sensor responds to the O2 reading. This causes the engine mixture
to be slightly off. You should change them, but you probably won't
notice much difference in the car. You might see a couple of percent
improvement in mileage, but you really have to be taking careful
calculations to notice a couple of percent.
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