D2 S8 - Big end gone?

[tintin]

In my experience, the sound of cats failing was a bit different from what you described - less rev-dependent, and it was fairly easy to determine that the sound was coming from under the car - i.e. where the cats where - rather than further forward in the engine bay area.

Good luck diagnosing and then fixing though, and hopefully it's something minor...

[Goran]

It depends on the failure mode of the cat, ie, random luck .
In my case a smaller corner piece was trapped further down the exhaust acting like a rattle powered by exhaust pulses. Therefore like a musical instrument it rattled at higher pitch as throttle increased and became louder. Therefore going back on what I said earlier removing the cats may not stop the noise. If the same thing has happened to your 8 the mechanic may have to fish around in the exhaust to remove the offending piece of cat.

[RS6]

hope its not too bad mate

hopefully its the cats, if it was doing it on rev's sounds like it could well be

Have you got the engine management light on?, surely it would of gone into limp mode if something catastrophic?

[briang9]

Originally Posted by HPsauce

More likely one of the catalysts, they can make a hell of a racket!

yes I agree, I thought same as you when mine went, can be very loud and does increase with extra throttle, you can get non Audi cats for a fraction of the cost of OEM, however as above they can throw the EML, I just bought a simple code reader from ebay for around a fiver which cancels it. You could get the sensors coded out but at the £350 I was quoted it's not worth it IMHO.. hope its not too expensive for you

[RICKY D]

Thanks for all of the encouraging words guys, it's been appreciated while I've been worrying about it for the past few days.

I got the beast on the ramp today and had a good look with my mechanic. He immediately said its one of your cats breaking up internally (offside one) but he could understand why I thought it was the bottom end knock from outside the car. Underneath it's much easier to see/hear it's one of the cats.

I feel a little silly for panicking now

Thanks to you guys who pretty much diagnosed this well in advance, I was at least able to get some sleep the past few nights

Thank you all ( one relieved S owner)

I have no EML on at the moment but as more breaks up will this trigger it? Thinking long term I guess I will need to replace it. Adrian I will have a search for your thread as that sound like a good compromise. As much as I like OE parts; £950 each

[Adrian E]

Just be careful if you're sending them off that you get it in the smallest box you can (I got a bike box from Evans Cycles but they came back in a much smaller package, somehow!) as the couriers will try and rob you blind.

I found mine a bit more responsive and louder after the cats were changed - they fit 400 cell metal ones that are much higher quality than OEM, by the looks of it.

Total cost for 2 to be done would come in less than an OEM replacement for one side, and you have peace of mind if the car's a keeper. That's ignoring the not-insubstantial labour to remove 2 cats! A lambda probe is bound to strip as well....

[RS6]

any updates on this?

[RICKY D]

I've been meaning to update since Friday.

I noticed the EML ping up on Friday morning followed by a very throaty sounding engine and unable to rev above 5k rpm.

I scanned the code and got P0430 - Catalyst System; Bank 2: Efficiency Below Threshold.

I suspect a large chunk of the internal cat broke off and became wedged somewhere further down the exhaust. I've reset the code but the car has no power, sounds rough and feels no where near as smooth as it should.

I'm at the stage where I'm not sure what direction to go.

1. OE cat from Audi
2. two refurbed cats from Germany as per Adrian E's write up
3. 200 cell sports cats with the EML issue coded out by MRC or similar.

I've lost motivation at the moment. The wife curbed 2 wheels the other day, then she managed to lose a fog light grill, I have a parasitic battery drain and then I have the issue with the cat!

Tempted to park her up and forget about her for a few months and hope I get the itch again

[RS6]

let us know what you do and how much and were? i know i will be next!

im just the same had major work done £'s!, then a coolant leak a month later! which has taken all my savings, now i have lambda sensor playing up

[Adrian E]

Depending which lambda sensor, they're not too bad to do. One is high up on the offside, but the nearside ones and the offside rear can be accessed easily enough and the wiring just runs through the floor of the car into the cabin.

Cost about £100 and ideally needs a cheap tap (under £10) to clean the threads before putting the new one in. One looked mullered on mine but after re-tapping the replacement went in fine.