EVAP help please

[Spindle]

We bought our RS6 in October and it is a lovely car with only one fault - P0441 EVAP Emission control 002 incorrect flow intermittent.

The guy we bought it from had already replaced the N80 and made us aware of the fault saying he thinks it is the charcoal canister. The car runs fine, just the annoying light on the dash.

Skip forward a bit, and I have been putting some time aside to drive it to work and investigate the cause of the fault. I found he had replaced the N80 with a non genuine one and had forced the original one out of the pipework leaving damage to it. I have replaced the valve and the pipework with brand new genuine Audi parts and while I had the old one off I tested it and it does not hold vacuum where the new one does. BINGO I thought! Swapped the new part and hoses in, cleared the code with VCDS and drove it home which is an hours drive. Light stayed off.

Drove it back to work the next day, another hours drive and the light pinged up just as I pulled into my carpark

So on to the next component - charcoal canister. This absolutely stank of fuel and was really heavy so I fitted a brand new one, again genuine Audi part. Cleared the code, drove home, light stayed off. Then on our drive to Cadwell Park the light came back on again

Now as far as I can see from diagrams the rest of the system is fairly simple pipework.

I need to check all of this as well as the fuel cap.

I am trying to eliminate everything by testing it and replacing it if there is the slightest hint of fault but my question is has anyone been through this saga with theirs and what did you find was the cause please? As much as I enjoy driving it to work and spending time on my own car instead of customers cars it is not very profitable so I'd like to get to the bottom of it sooner rather than later.

Any advice on what and how to test parts of the system are welcome!

[IanH755]

There's literally just 4 things in the system, the fuel cap, the N80 valve, the carbon canister and the pipework, so having replaced everything else so far maybe look at the fuel cap or maybe a pipe/connection has rusted/split.

To find a split etc you could try a vacuum test at the canister end as the N80 should be blocked if its working correctly and provide something to "suck" against, to see if there's a pipework leak at least.

[Spindle]

There's literally just 4 things in the system, the fuel cap, the N80 valve, the carbon canister and the pipework, so having replaced everything else so far maybe look at the fuel cap or maybe a pipe/connection has rusted/split.

To find a split etc you could try a vacuum test at the canister end as the N80 should be blocked if its working correctly and provide something to "suck" against, to see if there's a pipework leak at least.

This is my thinking too, I'm going to get a new fuel cap partly to eliminate it from the system and partly because the little rubber thing that attaches it to the car is all twisted and irritating to look at so it might solve two issues!

I'll have to check the hoses as the next actual job.

Thanks for the suggestions, when I solve it I'll update the thread so it has an end and solution - too many problem threads never post the answer!