gk1

Here is the latest update regarding my CEL carbon buildup issue.

History here:

https://www.audiworld.com/forums/sho...php?p=23927685

and

https://www.audiworld.com/forums/sho...php?p=23935899

They have performed the manual intake valve cleaning and also manually cleaned the fuel injectors.

I did get a chance to speak to a service adviser who had some technical knowledge and had also spoken to the regional technical representative about these carbon buildup issues a while back and here is the short detail of what he said.

He states the latest TSB which I had performed about a month ago changes the valve timing to modify the valve overlap (when both the intake and exhaust valves are open at the same time) to prevent excessive deposits on the intake valves. However the order in which they perform the service is upon initial complaint to perform the TSB update, then if the CEL comes back to run through the Audi fuel additive, check again, and only then do the manual valve cleaning.

He states that Audi is confident the software update will prevent this issue from re-occurring but the dealership suggests using the fuel additive monthly and as always they re-stated to use top-tier fuel only.

Unfortunately only time will tell if it is truly solved and for some it may be too late as they have abandoned the brand or DI technology altogether. However, I'd like to believe Audi worked their hardest to resolve this since almost all of the current engines are DI and a statement like "this is common on all direct injection engines" might be problematic for their future sales. They do need to disseminate this information to their enthusiast crowd in a better/quicker way or risk losing them.

JackKrash

Mine is in the shop for the last 5 days for the same issue. In my case the CEL's started right away - with the gas the dealer put in. Of course they told me the line about the fuel when I brought it in.

I finally told them to keep the car until it is fixed. Unfortunately in my neck of the woods loaner cars are not given out.

I am curious to see if the symptom comes back in your case, I am convinced the service guys in Brooklyn are reading your posts for ideas of how to fix the thing...

2008A6

Keep us posted...i did the TSB update and no CEL yet..
Though my service guy is ready and willing to do the cleaning anytime I'd like. Not sure if i should wait to see if the CEL comes back and I'm not sure that fuel additive will accomplish anything.

The G Man

The fuel additive will clean the injectors but not the valves.

audi bug

I like to share my research about intake valve deposit for DI gasoline engine.
Unless stated, I am not associated with any of companies or products I mentioned.

A. Source of intake valve deposit

This paper explains the sources of valve deposit.
http://www.atc-europe.org/info_/public/doc52.pdf
The sources of deposit are (on page 17 to 19):
Air contaminants
Engine blow-by (PCV)
Cylinder blowback
EGR
Oil (Oxidized materials and suspended insolubles)
Gasoline ( Thermal and oxidation degradation materials, Gums)

However, 3.2 FSI does not have EGR system. Main cause of valve deposit is vaporized oil, which is not trapped by oil separator, drawn into intake through PCV system. Since DI engine have fuel injectors directly in the combustion chamber, there is no chance fuel can clean the valve deposit.
The book I quote below has a good explanation of PCV and blow-by

B. How to eliminate the intake vlave deposit

Method 1. Bypass the PCV and dump into exhaust: This is not good for environment.

Example here.
http://forums.vwvortex.com/zerothread?id=4387972

Method 2. Additional catch can (oil separator) installed between PCV valve and intake.

Example here.
http://forums.vwvortex.com/zerothread?id=4752703&page=1

There are many discussion about different catch cans in VWvortex forum.
The above post is interesting because it has a couple of pictures of oil caught by catch cans. A person, living in Connecticut, using a catch can for 20,000 miles reported that there were very little oil caught in summer but a lot in winter time. Therefore, people in cold regions will have more issues with carbon deposit.

Method 3. Engine control strategy.

I found this very interesting patent granted to Ford on 8/31/1999.
http://www.freepatentsonline.com/6178944.pdf
Ford just has DI gasoline engine on the market but figured out the solution for valve deposit way before. I was very impressed. Disclosure: I used to be a Ford engineer until 2006.

The highlight of the patent I quote: “additional fuel is injected during the overlap of intake vale and exhaust valve. The additional fuel is thereby drawn from combustion chamber, past intake valve, into intake manifold. Subsequently, during the intake stroke, the additional fuel is drawn back from intake manifold, past intake valve and the surrounding intake port to clean carbon deposits accumulated on and around intake valve. --- Fuel which is injected during intake stroke is reduced in proportion to the additional fuel added during (valve overlap) to avoid an increase in torque which might otherwise occur.”
It also mentioned about auto detecting valve cleaning cycle and the valve cleaning is done only in homogenous air/fuel operation (see below about the explanation of homogenous operation).

This seems related to what gk1 was describing about TSB 2020645/3: modifying valve overlap.
My guess for Audi’s intention per gk1’s description is:
First, do TSB and see if it cleans valve deposit and fixes the problem. If that doesn’t work, add fuel cleaner to help it out. If that doesn’t work either (it will be the worst case), go for the manual valve cleaning.

For the explantion of three combustion modes of DI gasoline engine in laymen’s terms:
Charge Stratification mode –light throttle and low rpm
Homogenous lean mode - in between
Homogenous mode – heavy throttle and high rpm

please see this book for detailed explanation.
http://books.google.com/books?id=xWD...age&q=&f=false

Read page 27-29 (Chapter 3) for explanation of three operating modes.
Read page 280-281 (Chapter 11-3-2) for valve deposit.
Read page 291-297 (Chapter 11-5) for crank case ventilation and oil separator.
You can browse limited amount of pages in Google Books. You may be able to see all pages I mentioned if you are lucky.

There is disappointingly short one page (because I bought this expensive book) discussion on valve deposit on page 280 and 281. However, one important thing it stated is that intake valve temperature between 170 and 280 degree Celsius supports the formation of carbon deposit; beyond it, the residue burns off.

The TSB and the valve temp effect above make you think driving hard is better (homogenous mode) to lessen the valve deposit specially during winter time.

I was looking into installing a catch can but passed it because I figured every 55000 miles I need to change the cam follower for high pressure fuel pump. And I might as well do carbon cleaning at the same time since most of parts will be removed anyway for that job.
https://www.audiworld.com/forums/sho....php?t=2765010

In my humble opinion, this cam follower is the weakest link for 3.2FSI engine. Carbon deposit can be a trouble, but I can deal with it. However, if cam follow is worn out, the cam shaft needs to be replaced. I don’t know if I can tackle that. I planned to replace the cam follower at every 55K. Since cam follower job will force you to remove serpentine belt and coolant cross-over pipe, valve cleaning, coolant, and serpentine belt will be done along with regular 55k service like spark plug, air filter, and etc. In addition, I was going to seaform through vacuum hose at every other oil change.

C. What to do
Having found this TSB and guessing what it does, I will do following to mine:

1.Inspect the intake valve deposit.
2.Use VW/Audi approved oil (I use German Castrol 0W30 from Autozone)
3.Have TSB done (it will be nice to do spark plug coils at the same time if availble)
4.Use gasoline with high deposit cleaning agents like Chevron with Techron, Shell Nitrogen Enriched gasoline, or use Techron with other brand of gasoline.
5.Drive hard in any chances I get and tell my wife why I have to do that
6.Enjoy hack out of it while doing so!
7.Check the valve deposit on next oil change and see how effective the TSB is.
8.Develop next actions based on the result

2008A6

Thanks Audi bug - great write-up!

tmiele

Just got my S6 back from the dealer again (after seven days). This time they replaced all the injectors (last month they replaced one or two injectors, along with two intake manifolds and few fuel and air valves). It appears that the CEL light was still on after replacing all the injectors. They then replaced two fuel filters and the air filter.

After test-driving it for 350 miles over the last seven days (someone at the dealership had fun with my car) they finally released the car to me today after being at the dealership for 50 out of the last 56 days with the CEL issue.

This is very scary for anyone looking to keep an Audi with a DI engine past the factory warranty.

zzz4

So, is the CEL off now? Seems like the problem was clogged fuel or air filters after all?

NoVA_A6

I shouldn't have read this thread. I haven't had any CEL come on but the other day I was getting on the highway and a car sped up to try to block me. I put the car in sports mode and stepped on it. I noticed a lot of black smoke coming out of the back. I haven't gotten on it like that in a long time.
Could this be too much carbon?

tmiele

Today the light was off for the return trip home from the dealer. The car was returned to me three times with the CEL light off in that 57-day period. The light came back on within a day or two after leaving the dealership.