Issues with my RS4 cat converter, carbon & emissions light

[oxblood8]

Hi all,

Currently having an issue with my 2006 B7 RS4 Avant. About a month ago the emissions light came on on the dash. Took it to my local mechanic who reset it but said it may come back on again. It did indeed light up again a couple of weeks ago and I had the right O2 sensor replaced behind the cat converter. This was caked in carbon. After a week of driving the light came back on. Took it into the mechanic and after running the engine for a little bit (idle, then slightly more revs) the temperature of the right cat was less than the left (around 50 degrees less). The actual fault that it is throwing is Catalytic converter bank 1 efficiency below threshold.

Mechanic suggested that the cat converter could be faulty which of course is not good news. Next step is to remove the cat for a visual inspection.

If it turns out the cat needs to be replaced, I guess the options are to purchase a new factory cat for the right (leaving the left as is), or go for a pair of aftermarket downpipes.

Ideally what I would like to do with some aftermarket downpipes is to just have these bolt straight on to the existing stock exhaust and not cause any CEL issues. However after doing some research, there doesn't seem to be any (not that I have come across) downpipes that will achieve this. Do you guys know of any?

Bit of history, I am from Australia, the car has not had a carbon clean, has 82,000kms on the clock and I believe was a city car before I owned it so assume it was primarily driven around the city most of it's previous life (I live in the countryside).

In terms of a stock replacement, it would probably be best for me to source one from a member either in the US or UK who has removed theirs. Being in Australia, there are not that many RS4s over here to begin with and even more rare to find someone who has replaced the stock downpipes.

Just after some advice on what you guys think would be the best approach for me to go.

[oxblood8]

OK so here's an update on my car.

Went in for the carbon clean yesterday, my mechanic said that the intake manifold wasn't as dirty as he thought it would be however the top of the valves were absolutely caked in carbon. As you can see from the pics, the port separators were really dirty as well.

The worst however was the pre-cats on both sides. They did not remove the downpipes but were able to put a camera in through the upstream O2 sensor hole. All you could see was a bit of the honeycomb material on the outer edges but the main section was completely blocked up.

So what I am thinking now is to de-cat (piggie) both downpipes (remove only the pre-cat) and either run some O2 spacers or relocate the main O2 sensor after the main cat to avoid CEL. Couple of questions around this:

1. What spacers are people buying these days? I could only find some very old links to spacers which were dead links.

2. On the relocate, is it as simple as welding the bung behind the main cat, screwing in the O2 sensor into that then plugging up the old hole?

3. Where are you guys buying the bungs?

Here are some pics

[NY07RS4]

You've checked all of the boxes. Good job. Most wouldn't have done the research prior to coming here and asking questions.

To answer your questions:
O2 spacers and or bungs - you have a few options but a lot of people like the Draft 42 Designs options
http://www.42draftdesigns.com/exhaus...icedesc&page=2
Another option would be Vibrant:
http://www.vibrantperformance.com/

As long as your mechanic or welder does a bit of thinking and planning prior to relocating the bung you should be good to go once done. You want ease of access once relocated and also want to make sure you have enough slack in your wiring to reach the new location.

The spacer is self explanatory.

That's a decent amount of carbon. On top of the small performance bump you'll be removing a ton of heat from the area by removing all of that carbon. Same deal from removing the pre-cats. Your engine will thank you for that and the new found performance is your reward.

Enjoy and keep us posted.

[oxblood8]

Cheers mate thanks for the reply.

I've done a lot of reading the past few weeks and have received a lot of great advice from forum members over at RS246 and Ozaudi here in Australia.

Can be hard to wade through all of the information at times but there is a lot of good info out there if you take your time.

The next step now is to remove both downpipes for de-cat. Thought this could be a task I could do with my Dad as he has a hoist and is pretty handy on the spanners. However after reading some posts on people removing their DP's and snapping the bolts, I think its probably best it's left to the pro's.

For the O2 CEL issue seeing as I will have both DP's off the car, would I be best to re-locate the main sensors or just go with the spacers? I've read differing accounts of what works best and thought I might as well go with the one that's most successful instead of having to take the DP's off again at a later stage.

So after all of my research I really can't find a definitive answer as to preventative measures post carbon clean. I've read that an oil catch can doesn't do a lot and similarly the Water/Meth Injection kit, with those who have installed have seen little to no improvement on the carbon buildup. So in saying that do you pretty much just have to factor in a carbon clean into your maintenance schedule every now and then?

I'm looking forward to the end result to see the difference in the car. I thought yesterday when I was out driving it felt a little bit more responsive post carbon clean.

[NY07RS4]

Relocating the bungs are your best bet. More work than adding spacers but worthwhile since this is almost a surefire way to avoid the CEL when running piggies. The good news is you can add spacers to the relocated bungs, twice the insurance so to speak.

Factor it in. No one can mitigate the build up, it's inevitable and really not a huge deal.

Good luck.