silverRS4

The dealer did not say. Since they only put 25 miles on the car during the repair, I assumed they just flushed the fuel line and the injectors with the concentrate. Several injectors failed the following leakdown test just as they had prior to the flush. So, they replaced all the injectors, which I appreciated.

ELEVENS

I can't figure out why carbon buildup on the backside of the valves would effect ignition timing.

silverRS4

Because the same buildup that's on the valves is also in the combustion chamber. This is hardly speculation. The top of the piston and the spark plug are relatively clean due to the intense temps of the flame front. The bore is naturally clean due to the wiping of the rings. But the upper perimeter of the chamber can have the same epoxy-like buildup that is evident on the valves. It is this buildup, along with particles dislodging from the intake valves, that can damage the injectors. Just how the injectors are damaged, I don't know. In any case, they can no longer hold the residual pressure in the fuel system (or the test pressure when the dealer checks them). They slowly leak fuel into the cylinder. Upon start-up there is too much fuel in the cylinder and a misfire can occur. That is the advanced stages of the buildup are identified by a engine that runs very rough upon cold-start (it may or may not throw a code) and then runs better within a couple minutes. To answer your question, any source of carbon-based buildup in the combustion chamber of a 12:1 engine can definitely be a point of pre-ignition. Luckily, one of the 4 knock sensors detect it and pull out timing in the respective cylinder.

STALKIN RS4

So at the end of the day, what is the solution to the problem????
The solution is not having to take if your intake manifold and have to clean it out IMO. Is Audi working on a solution even?

ELEVENS

Carbon inside the combustion chamber can probably be dealt with using fuel additives, such as the Biosyn which I use regularly. Never used a fuel additive before, but I sure as heck am on this car. I thought the RS4 CR is 12.5:1?

SilverCanuckTT

I'm wondering whether (once cleaned) even simple water injection could keep the valves clean. It certainly would keep the chamber clean. That's been proven for years. However it would be a pain to have to keep filling a water tank.

Another thought I had is that a simple electrical vacuum pump could be used on the tube on the cyclone that normally goes to the inlet manifold. That pump could pump the oil into the crankcase instead of the intake. Keeps the system closed, but provides a better path for the oil.

Lots of cars have used such vacuum pumps for brake boosters and emissions, but I haven't seen one used in this manner.

SilverCanuckTT

Correction: vacuum pump on the return tube of the cyclone that goes to the crankcase.

There is an oil drain valve in that path that only opens at low rpm where the pressure from the valve covers and the bottom of the crankcase are about equal. A vacuum pump would force the oil collected by the cyclones into the crankcase all the time, not just at idle.

RS Maniac

Correct, CR is 12.5:1 (see pp.31)

http://www.jlosee.com/images/RS4/PDF/RS4_launch_doc.pdf

B-, def buy yourself one or two of the fuel additives, just keep in mind they are super concentrated.

I embrace the fact that people are thinking of ways around this, but the truth is it would not be 'rational' to mod your engine before the end of the warranty. Even if someone figures out a great solution (oil catch can or other) that is proven to work, I am sure AofA will void any warranty on the premise that the engine was 'tinkered' with. While I cringe at the thought of having to go get my manifold cleaned every oil change, at least it will be done with full warranty. Once out of warranty, that's a diff matter. I am (or should say - was) planning to keep this car for many years, but should I get a sense this is indeed spreading like the plague, I will have to dispose of it before warranty expires, unless AofA has an official recall and remedy... Speaking to my tech, he did acknowledge this is widespread across FSI engines, not just on RS4s.

In fact last week he had an R8 for the same issue. Coincidentally, that same R8 was burning 1 qt oil every 500 miles, which I recon is excessive. Wonder if there is a direct relationship - i.e. cars exhibiting excessive oil burn (be it because of bad break-in or other) are more prone to CB.

SilverCanuckTT

I bet you are right. That oil has to go somewhere, and it has to be out the tailpipe via the intake scavenging. Maybe the cyclones can't deal with the excess oil that badly sealed rings dump into the system ?

The G Man

I have a 08 A6 with the same problem, dealer said Audi is working on a new ECU program that reatard the timing to fix this problem. SA also said this is a problem with new Audis during break in period and the problem will not re-occur. What do you guys think, will the problem re-occur?