Help Please EPC mystery on S4 B8.5 (2012)

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ryanofford

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Hi,

I'm trying to solve an EPC light problem that is eluding us at the moment.

It seems to only kick in at high revs as the gear change takes place (DSG gearbox).

If I don't drive it flat out then the car drives beautifully. Anything that has needed doing has always been done.

It's only happening on one bank of the engine (passenger side) as a multi-cylinder misfire. Engine off/on and we're good to go again. My local Audi specialist (independent) has drawn a blank now so I'm getting a little stuck as to what this could be.

The car has 68k miles on it, just had a major service (by Awesome GTi). Plugs were changed so it's not them. We've tried changing coils and it's not that. There was a suspicion of it being a VVT controller (Inc cleaning out a mesh this has apparently).

We then moved onto the swirl flaps (whilst fixing a coolant leak under the supercharger). This had a new pump and hosing and I thought we'd cracked it. Several enthusiastic tests on an empty road worked fine but then I've been able to trigger it twice.

Getting stuck for answers. Help appreciated.

The car has a Revo Stage 1 tune, K&N filter and an x-pipe (all of which have been on for a few years).
 
Ooh! Subbed for answers, as i have exactly the same fault!!

Been happening on and off for 6 months.. i also have changed all coils and plugs, and always the fault is on the same bank (cyls 4 and 6).

Back of car (ie firewall)
3 6
2 5
1 4
Front of car (ie crank/sc pulley)

I am stage 2 with 73k on a 2014

Other things i guess to start looking at would be wiring, dirty valves, or fueling?!

Good luck.

Cheers
goose
 
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I've stuck a fuel additive in tonight (cheap and won't hurt to try). It'll take a little while to go through a tank but it feels a little smoother and didn't happen on two 'tests'. Will let it run through and see (actually bought two so I'll try the other one in a week or two). Will post when I crack the problem.
 
I finally have an answer after around 9 visits to my garage (Sale VAG centre) plus another (ex Audi Master Mechanic - RGH Audi in Knutsford)

TLDR The catalytic converters have melted.

RGH suggested this was a possible candidate so I did some research and stumbled across this

View: https://youtu.be/Iz7jpf-5abw?si=vR7B2psqz7eBo4LN

That led to more searching to find it does happen on the 3.0T V6 engine and can happen a little earlier if tuned. It goes on one side first (passenger). EPC light and multi cylinder misfire codes are all you get.

Anyway, a borascope was deployed and yep, they are in a mess.

Trying to find somewhere to fix it is the next battle but at least I have an answer and some options.

Being high up at the back of the engine is the problem for heat soak and it's also why it's quite a few hours labour to sort. Current best quote is for sports cats and ~10 hours work (so £2.5k maybe).

At least it's an answer. Hope this helps someone else out.
 
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Aah glad you got to the bottom of it..

I took the preventative (and cheaper!) measure of having my stock cats removed/gutted/refitted. Cost around £800 iirc due to labour time.. it does make the car more raspy, but not too crazy.. and you do need to befriend your local MOT man, but that's nothing for the peace of mind knowing i won't grenade the block now :)

goose
 
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Have got my car booked in for JHM catted and baffled downpipes with Xatrix in Bradford. Really struggled to find anywhere to take the work on. Audi costs were £2.5k each plus fitting. All in these will be £2.3k estimated. Hoping to save some labour costs with cutting bits of the cat to extract them rather than taking the gearbox off.

The car goes in for the work in just over a week's time.
 
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