Victim is a 2003 A6 2.7T MT6 with 195k miles. It has a GIAC chip, Samco TBB, Baily DVs, and a stage 2 AWE clutch and LWFW. It is not raced nor tracked. My catalytic converters are throwing codes and I am interested in replacing the whole system.

I searched the forum and found nothing for A6 2.7Ts. Most threads are for the 1.8T, so I am throwing this out for anyone with direct product experience or even an opinion.

I am interested in the APR kit from ECS Tuning (Audi C5 A6 Quattro 2.7T > Exhaust > Down Pipe > ES#4379 Downpipe Kit - CD100004 ). Has anyone installed this and what was your experience with fitment, elimination of CEL codes, use of cats versus test pipes, increase in sound, other issues or problems encountered while installing or using??

While I am mostly interested in eliminating the CEL from my old failed cats, I am also using this opportunity to pick up a little performance and prepare the car for the eventual replacement of the oem turbos with a K04 kit. By the way, the car is not raced or tracked, but I enjoy the rush on the highway when I hit the accelerator.

 

check with VAST and/or RAI. I know both sell downpipe kits for the C5 2.7T. I'm sure you could give either shop a call and they would be happy to answer your questions. IIRC, however, installation is a PITA. Like doing the turbos, step 1, pull the engine...

I'm not positive it is that bad though. I'd be interested in the "real" answers to your questions

 

Still doing the research here and on audizines. I don't believe the engine needs to be pulled although reaching the turbos is a real pita. My indie shop figures on about 3 hours work for the install.

One question to throw out there -- is there any way to test the O2 sensors in the rear cats? One feedback is that it could be the sensors and not the cats.

I'll post the codes when I get home. Interesting patter: the codes are cleared and then come back after a few hundred miles. It's not like I drive around town for weeks with short trips. Two weeks ago they were cleared, and they came back 250 miles into a drive to Ann Arbor. Cleared again two days ago, and yesterday they came on 350 miles into a trip to upstate NY.

 

Just returned from a 1200 mile trip and the CEL went on 350 in. The only code showing is P0421 - warm up catalyst efficiency below threshhold (bank 1). Does this sound like bad cats or bad sensor??

 

If I understand it correctly, the computer calculates the cat efficiency by comparing the O2 readings pre-cat and post-cat while factoring in fuel trim and and intake air flow. Potentially a bad O2 sensor or the ECU being "confused" by some of the various readings. I think there is a way to measure some of the individual blocks with the vag-com and then by doing a few calculations you can figure out whether it is a cat problem or one of the sensors. unfortunately, I have know idea how to do it. i really wish there were more than just the two of us in your thread