Hi all.

I'm new here so be gentle. I'm pretty much a newbie when it comes to Audi's, even though I've owned one since '03. I usually had the dealer do the work, but now that my car is approaching 12 years old (my '99 was built in '98, go figure), the value of my car is not too much higher than it costs the dealer to put an all-new exhaust system in.

I've done some searching around on this site and elsewhere, but I'm having some difficulty coming to any conclusions regarding the exhaust system for my '99 A6.

Right now, both of my cats are rusting out. One is pretty much completely void while the other one appears to be somewhat okay aside from rust. The two things in front of the cats that look like a stainless steel braided ball of thread (don't know what those things are called) are coming apart as well. From there back, I think the resonator is okay as are the mufflers, just rusty. I'm not sure about the O2 sensors on the Cats. From looking online, and from the sparce info about my car that I can find, I get the impression that there are 4 O2 sensors?? 1 inflow and 1 outflow per Cat. Is this correct? I'm not sure if these are good or bad. I do have a check-engine light on, which the Audi dealer tells me is exhaust related. Of course, they just tell me I need everything from the headers back as the ask me to bend over...

Overall, my car sounds like crap and I'm practically embarassed to drive it. Almost as bad as my Jeep which I pretty much only use for off-roading which doesn't have exhaust at all.

I'm looking for a hopefully inexpensive-as-possible exhaust system for my car. I've get the impression that dropping the Cats altogether is a bad thing, and I've gotten several recommendations from people to basically replace everything from the headers back with stock Audi cats and pipes. Then from behind the cats, I can do anything I want. Is this also correct?

Beyond the Cats, I think that I'd put in Magnaflow exhaust, as I've seen several resonators that I think work for the A6 and are about $100 bucks or so instead of the almost $400 from audi.

One thing I haven't been able to find online is just a complete exhaust system. Several years ago when I first started noticing rust on my exhaust, I looked into several performance exhaust systems for my car which were remarkably less than Audi's stock parts. One even being a stage 2 exhaust. Unfortunately I can't even find that anymore.

If anyone has any suggestions or can point me in the right direction, please help.

Thanks!

 

You're going to need to replace all four O2 sensors for sure...most states require then to function correctly in order to pass some sort of inspection. Generally speaking, when you replace one catalytic converter, it is highly recommended that you replace the O2 sensor(s) as well even if they are still functioning. The braided ball that you referred to, which is actually called a flex pipe, shouldn't be super expensive. If they are starting to fray, the sound of your exhaust being very raspy is partially related to that since the sound has not been muffled yet seeing as how the flex pipes are at the very beginning of the exhaust system. The actual mufflers themselves can be swapped out for something more desirable if you want. I wouldn't recommend Magnaflow. For a car that old and if you're really concerned about cost, go with something less expensive. Magnaflow has about $90-110 performance-related mufflers and you can find some made by competitors for literally half the price. I bought two performance mufflers made by Pypes (a reputable exhaust manufacturer) for $37 a pop. All together with shipping, I was looking at like $87. $5 less for TWO mufflers as opposed to ONE magnaflow and they sound just as good. They are Pypes M-80 glasspack.

 

you can remove the cats if you have no emissions testing. i'm running without cats. occasionally i'll get a code pop up. the key is to upgrade your intake system. you need to put a lot more air into the engine than the factory intake can do. that should dilute the exhaust with enough oxygen to prevent codes. all you really need is a new muffler. i bought mine for around 300, but there are a lot less expensive options. if needs be you can pick up a few high flow universal cats for 60-80 each. a flex pipe, or resonator, is like 25$ at autozone. most muffler shops don't charge much to just weld on a few cats and a muffler. you can do it all for 500 easy. as far as replacing the lambda sensors, it depends on the condition of your old cats. if they are fine except rust, you should be fine. if they're clogged up or melted from unburned fuel, you may need replacement. yes you have 2 per bank. 1 before, 1 after the cats. i'd fix the exhaust first, then you'll know if and which o2's need replacement. they are expensive to replace, especially 4 at a time. you also need to get oem bosch o2's. don't get universal or an off brand. our cars are very sensitive to cheap electronics, particularly when it comes to such important input sensors.

if need more help ask. i've had my 2.8 for 8 years. torn down and rebuilt almost everything. i know it inside and out.

 

hey man i read your post & would like to request your knowledge. i have the p0411 error code on my 1999 audi a6Q built in sept. 98. i went to the junk yard & replaced the secondary air pump b/c the rivets were blown out & it made an awful sound so i pulled one from a vw passat 03' w/ same codes & the light came back on.... so i replaced the vacuum hoses on top that i could locate, rest the code & it came back... what direction would you check from here? thanks ahead of time.