Does the 1999 A6 2.8 have one catalytic converter or two? Does the car also have two pipes from the front of the car so it has two converters and two mufflers? I'm new to Audi (usually working on nissan, mazda, honda) and I'm checking out a used car that is missing a few parts.

 

Two of both

 

Not that this helps ALL that much, but it should be a little useful:

 

That diagram is exactly what I am looking for in this car. Which figure is the converter? Is there a key to that diagram?

 

None of those are cats. The middle thing is the resonator(7), two rear ones are the mufflers(10 & 13). There are two cats right after the exhaust manifolds, and two more underneath, right before the pic nm posted. 02 sensors only read off the upper cats though, so the lower cats are basically useless. Im gutting mine.

 

So the car has four? Is that diagram showing from the second set of converters back? Hmm I better take a good look before I buy this car. Seems to me I will probably have to replace the entire exhaust system. I'm not sure how much of the system is left on the car. I checked on eBay and I only saw a left and right converter. Well I'm checking the car today.

 

Right, that's why I said that diagram wasn't all that helpful. Here's one that shows how the O2 sensors and the cats work in tandem:

 

Except we dont have B1 S3 or B2 S3. Our B1 and B2 S2's are right before the cats yopu see under the car. You cant see the upper cats, they are burried.

 

There ya go, i X-ed them out on the picture.

 

damn.....you have 4 cats?
Had no idea are cars out there with 6 O2 sensors. Holy ****...