Error Code P0305 & P0491

[Triton3k]

Alittle backstory.

Good day everyone. I have a 2012 A6 3.0T premium. I ended up getting a check engine light and to find out what was wrong with my car I took it to Audi for a diagnostic. What they found was that Intake Runner Bank 1 needed replacement, secondary air cleaning, valve cover gaskets both needed to be replaced, and a Fuel injection cleaning. I pretty got ended up getting all the work done by an independent mechanic and I started getting misfires with an EPC light. First course of action was replace the Coils and spark plugs. The car was still getting misfires, I took it to a recommended mechanic who use to work at Audi, he immediately saw that the injectors were bad and replaced all of them along with a carbon cleaning. When testing the car it ran way better than before. But behold, check engine and EPC light comes on and we were getting code P0113 along with P012c, he then realized that he had to set the intake runners to neutral mode when installing them. Again car ran good for a few miles and misfires again but this time the shaking wasn't as noticeable as before but you felt it under 2K RPM. After some additional testing, we replaced the injectors for another set and now we're getting a constant misfire no matter what coil and spark plug we replace it with in cyclinder 5. Now we are getting code P0305 and P0491 with the EPC light. At this point I dont know what else to try and do. I did set up another diagnostic appointment with Audi to see what they say. But any leads anyone here has please share them if you've similar situatioons.

[Valpo A7]

Gotta love the diagnostic parts cannon.

If you keep swapping plugs and coils and the cylinder 5 misfire stays then it’s not plug or coil problem. You need to run a compression test and determine if you have a dead hole or not. It’s possible that the carbon cleaning is not complete and you still have a valve hanging open or maybe it’s a damaged valve or maybe it’s a ring issue. But first (and the mechanic should have known already) get a compression test done. The P0431 code is a secondary air problem with bank 1. Both might clear up at the same time.

[Burkeomatic]

Off the top of my head you could have a leaky manifold gasket there, but I doubt it. (A leak would cause air to leak out under boost and cause a rich condition).

My car had a cylinder 5 misfire and it was the timing chain causing it somehow, it was present with the timing codes however.

You need fuel, spark, and compression, if you aren't getting one of those, that causes it. You have already ruled out fuel and spark seemingly. Could be if the injector is bad, the damage is done.

[Triton3k]

Gotta love the diagnostic parts cannon.

If you keep swapping plugs and coils and the cylinder 5 misfire stays then it’s not plug or coil problem. You need to run a compression test and determine if you have a dead hole or not. It’s possible that the carbon cleaning is not complete and you still have a valve hanging open or maybe it’s a damaged valve or maybe it’s a ring issue. But first (and the mechanic should have known already) get a compression test done. The P0431 code is a secondary air problem with bank 1. Both might clear up at the same time.

Yes the next test is going to be a compression test. At this point I'm gonna take it to Audi and see what they say.

[Triton3k]

Off the top of my head you could have a leaky manifold gasket there, but I doubt it. (A leak would cause air to leak out under boost and cause a rich condition).

My car had a cylinder 5 misfire and it was the timing chain causing it somehow, it was present with the timing codes however.

You need fuel, spark, and compression, if you aren't getting one of those, that causes it. You have already ruled out fuel and spark seemingly. Could be if the injector is bad, the damage is done.

gotcha.

I hope no major damage has been done. Really hoping to get her back up and running.

[Burkeomatic]

gotcha.

I hope no major damage has been done. Really hoping to get her back up and running.

I could give you a laundry list of oddball things I have seen in my time spinning wrenches that could/have caused a single cylinder misfire, but there is no sense throwing that many parts at it and you losing sleep over it. Getting a proper leak down test would be best. Sometimes you can tell with those el cheapo compression testers you rent from autozone, but a leakdown test is the best. If it comes back dead on the autozone tester, you are screwed though.

If the compression test comes back good, that is a huge sigh of relief, then you know you are just chasing some electrical gremlin. It could be something as simple as a wire got nicked or kinked, who knows.

[jrsAudiA6]

If it is a misfire on just one or two cylinders another possibility is one or both supercharger inter-coolers are leaking. This is more common then you might think. I had to replace both inter-coolers on MY12 A6. One was leaking bad enough to cause a misfire, thou it was intermittent.