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Thought I would make this easier by posting a thread that Condensed several papers, articles, and photos here to give some insight into the real world of every DI engine out there (please excuse the PR spin quotes on how every automaker still denies they have this issue) and pay close attention to the dyno documentation of before degradation as the miles accumulated and the amount of lost power and economy over time:

This is 68,000 miles on one installed RX system next day after picking car up at dealer VS 55,000 miles w/now can on. Same engine, same vehicle, same year:

Intercooler at 15k miles w/no can....notice the amount of baked on residue has restricted the flow through the core already to a point, and is insulating it reducing the ability to transfer heat:

16k miles with RX system installed at less than 200 miles (new). Notice zero deposits or baked on residue...even on the SC rotors:

55,000 miles with no can:

Different vehicle at app 40k miles w/no can, same engine disassembled to do entire valve job as valve guides were worn excessively due to the deposits on the valve stems:

68,000 miles w/RX system installed at less than 100 miles (new)

Only a dry light coating without the clumped oily big flow obstructing deposits the without pictures show.

These would be the most accurate over an extended time. We would like to also have the vehicle back in at 100k miles to scope to see results at that time and hopefully longer. This has been over 4 years to get to the 68k mark and customer we hope keeps car longer.

Now here is a picture of the same engine, but the LY7 version that had Port Injection (same engine, same displacement but before DI was added) to show at app 114k miles zero deposits due to the old style port injection constantly showering the valves with detergent fuel preventing any deposits.....and note the spray pattern where it hit in the port as well no deposits:

On the effects of intake valve coking, there are SAE papers, Patents, etc. Here are just a few, and they go back quite away's so this is studied, and studied, and studied:

In the box is all the reference info for the entire study, etc.
Publication number US4811701 A
Publication type Grant
Application number US 07/201,894
Publication date Mar 14, 1989
Filing date Jun 3, 1988
Priority date Jun 6, 1987
Fee status Lapsed
Also published as DE3719077A1, DE3719077C2
Inventors Horst Buhl, Wolfgang Kleinekathofer, Eggert Tank
Original Assignee Daimler-Benz Aktiengesellschaft
Export Citation BiBTeX, EndNote, RefMan
Patent Citations (6), Referenced by (11), Classifications (11),Legal Events (5)

External Links: USPTO, USPTO Assignment, Espacenet
The coking of valves is a problem which has long been known, in particular in the case of inlet valves of Otto engines. Coking is understood to mean black, hard deposits which are produced mainly by combustion and decomposition residues of the fuel.
The requirements, which have been increasing for some years, imposed on the emission behavior, higher power outputs and lower fuel consumption, result in engines which are operated with a leaner fuel/air mixture. These requirements, as well as the use of unleaded fuel, result in the valves being more easily coked, and a coking of the valves manifests itself in a more troublesome manner than before.
The negative effects of inlet valve coking include poor cold running, poor gas admission, particularly in the warming-up phase, an increase in the fuel consumption and pollutant emission associated therewith, as well as a drop in power due to interference in the inlet air passage and out-of-true engine running. In addition, coke particles may damage the valve seating surfaces, which results in leaky valves.
Attempts to prevent coking of the inlet valves have included adding additives to the fuel, and also providing the valves with a layer which prevents deposits. Thus, it is shown in German Unpublished Patent Application No. 3,517,914 to provide inlet valves with a polytetrafluoroethylene layer. However, in practice such layers have not resulted in success.

References from the Audi engines and the studies, effects, attempted solutions, etc.:

S5 FSI engines doomed due to intake manifold carbon build-up ? CONCERN
Audi A5 3.2 v6 FSI - carbon issues? CONCERN EXTERNAL
Carbon Build up at 35K PICS

A6 3.2:

RS4: Intake Manifold Carbon Build-Up & Clean Up PICS
RS4: ** PART 2 ** Intake Manifold Carbon Build-Up & Clean U PICS
RS4 only 263whp flat from 6k rpm ?!?! PICS
Sea Foam useage? CONCERN
Cost to Clean Carbon? CONCERN
My RS4 under the knife... PICS
Fuel adatives.... PICS EXTERNAL
RS4 owners READ this! CONCERN
RS4 Owners Step in. What I feel to be very important. It's a long read. CONCERN
Need help, RS4 in shop for MILs, how does valve cleaning get authorized? CONCERN
Dyno after port, polish, manifold flap removal PICS EXTERNAL
Dyno info for the day... PICS EXTERNAL
***** Official Carbon Build-Up Thread ***** POLL
Carbon Build-up 101? CONCERN
KryptoniK's RS4 PES S/C Build PICS
2008 RS4 Carbon buildup EXPERIENCE EXTERNAL
FSI Engines - Audi RS4 Engine Oil-Related Deposits PICS EXTERNAL
Update on carbon cleaning.... EXPERIENCE EXTERNAL
My RS4 Carbon Build-up Story PICS
RS4 Supercharger Project Has Started Pics PICS
RS4 carbon cleaning finished !!!!!!! EXPERIENCE PICS
RS4 Piston Damage from Carbon Build-up PICS
RS4 : to prevent carbon build up, i think this product will work. CONCERN
RS4 inspected by AOA for CB EXPERIENCE
my RS4 needs help CONCERN
Throwin' Codes at 9900 miles - 2008 RS4 EXPERIENCE
Thinking of buying an RSs4. Does it have carbon problems CONCERN
B6 S4 paid off... 20K to put down on used Rs4 with lower miles.. Cant do it! CONCERN
My RS4 dyno numbers... PICS

R8 4.2:
FSI Carbon Buildup CONCERN

TT Mk2:
carbon buildup problem with TFSI - serious worry CONCERN EXTERNAL

Problem Synopsis
The general consensus is that the build-up that forms under normal operation can decrease engine power within a relatively low amount of milage. Most anecdotal evidence shows that when theintake valves are cleaned, engine returns to spec-rated horsepower and torque. This build-up is thought to affect power in as little as 10,000 miles though few people have routinely removed their intake manifolds to document the build-up progress.

A wide-range of variables have been included in reports of build-up. A common theme is that this occurs despite tier 1 fuel and Audi recommended oils. Reports have also come in from all over the world, suggesting it's not localized to any particular region's fuel, environment or emission standards.

Severe cases of build-up can potentially trip misfire CEL codes though in most cases, the car simply produces less power and does not indicate malfunction. Those that have cleaned their intake manifolds explain a burst of acceleration under WOT at 6k RPMs (2nd gear)(applies to RS4/R8 4.2). Dyno results for affected cars seem to be anywhere up to 40hp below quoted stock HP on the 4.2 V8 FSI engine.

To remove build-up, only a manual physical cleaning of the intake valves and vanes has shown to be able to completely remove the carbon of which Audi will not warrant unless there are continual misfires occuring. To prevent the issue from reoccurring, oil catch cans are the most frequently raised potential solution in addition to methanol injection. At least one thread has cited both of these systems were in-use and build-up still occurred.

There are a number of temporary cleaning solutions that are available. The effectiveness of these has not been discussed. Some of these include: BG 44k and Direct Injection Power 3. Audi's solution is a fuel additive to clean the injector ports, though this has been shown to have little to no effect on carbon build-up on the intake valves.

Audi has not yet acknowledged the extent of the carbon build-up problem. There is a letter that has been created by a forum member to Audi in this thread:

Official Letter to Audi of America Executive Vice President...Thoughts?

Publikasjonsnummer US6786433 B2
Publikasjonstype Tildeling
Søknadsnummer US 10/111,249
PCT-nummer PCT/DE2001/002710
Publiseringsdato 7. sep 2004
Arkivdato 19. jul 2001
Prioritetsdato 4. aug 2000
Gebyrstatus Forfalt
Også publisert som CN1237268C, 8 flere »
Oppfinnere Martin Maier, Joerg Heyse
Opprinnelig patentinnehaver Robert Bosch Gmbh
Eksporter sitat BiBTeX, EndNote, RefMan
Patentsiteringer (5), Klassifiseringer (26), Juridisk aktivitet (4)

Eksterne linker: USPTO, USPTO-tildeling, Espacenet
BACKGROUND INFORMATIONDuring operation of an engine, a problem generally occurs in the case of direct injection of a fuel into the combustion chamber of an internal combustion engine, particularly in the case of direct gasoline injection or the injection of diesel fuel, that the downstream tip of the injection valve projecting into the combustion chamber is coked by fuel deposits or that soot particles formed in the flame front are deposited on the valve tip. Therefore, in the conventional arrangement of injection valves projecting into the combustion chamber, there is the danger during its lifetime of a negative influence on the spray parameter (e.g., static flow quantity, spray angle, drop size, skeining) that can lead to operational disturbances of the internal combustion engine or to a malfunction of the injection valve.

And from VW engineering:

"Gasoline engines with direct injection of the fuel into the combustion chamber, i.e., not into the intake port, suffer especially from the problem of the formation of carbon deposits on components. Carbon deposits form especially in the neck region of intake valves. A more exact analysis of how these carbon deposits form leads to the following result: Oil and fuel constituents first form a sticky coating on the components. These constituents are chiefly long-chain and branched-chain hydrocarbons, i.e., the low-volatility components of oil and fuel. Aromatic compounds adhere especially well. This sticky base coating serves as a base for the deposition of soot particles. This results in a porous surface, in which oil and fuel particles in turn become embedded. This process is a circular process, by which the coating thickness of the carbon deposits continuously increases. Especially in the area of the intake valves, the deposits originate from blowby gases and from internal and external exhaust gas recirculation, and in this process, the blowby gasses and the recirculated exhaust gas come into direct contact with the intake valve.

Especially in the area of the neck of the intake valves, excessive carbon deposits have extremely negative effects for the following reasons: In the case of Otto direct injectors, the successful ignition of the stratified charge depends to a great extent on the correct development of the internal cylinder flow, which ensures reliable transport of the injected fuel to the spark plug to guarantee reliable ignition at the spark plug. However, a coating of carbon deposits in the neck region of the intake valve may interfere so strongly with the tumble flow that ignition failures may occur there as a result. Under certain circumstances, however, ignition failures can lead to irreversible damage of a catalytic converter installed in the exhaust gas tract for purifying the exhaust gas. Furthermore, the coating of carbon deposits in the neck region of the intake valve causes flow resistance, which can lead to significant performance losses due to insufficient cylinder filling, especially in the upper load and speed range of the internal combustion engine. In addition, the carbon deposits in the neck region of the intake valve may prevent correct valve closing, which leads to compression losses and thus sporadic ignition failures. This in turn could irreversibly damage the catalytic converter. There is the potential for small particles to break away from the coating of carbon deposits in the neck region of the intake valve and get into the catalytic converter. These hot particles may then cause secondary reaction and corresponding local damage of the catalytic converter. For example, a hole may be burned in the structure of the catalytic converter.

Globular deposits are found especially on the valve stem downstream from a partition plate in the intake port. Due to the dripping of high-boiling hydrocarbons from the partition plate towards the valve neck or valve stem, globular carbon deposits eventually form there by the sequence of events explained above. These deposits on the valve stem can result in flow deficits due to undesired swirling and turbulent flow around the globular carbon deposits. This may persistently interfere with the formation of stable tumble flow from cycle to cycle.

A possible solution would be to keep these sources of deposits away, for example, from the intake valve, by completely eliminating exhaust gas recirculation and the introduction of blowby gases into the intake port. However with the combustion behavior of modern reciprocating internal combustion engines, at least external exhaust gas recirculation and the introduction of blowby gases into the intake port are absolutely necessary for reasons of emission control and fuel consumption, so that this approach is not possible.

And from the site

It’s the next generation of fuel injection, which replaced the carburetor somewhere back in the ‘80s. By result of squirting fuel right into the individual cylinder, the engine gets a higher quality of combustion and an increase in combustion efficiency. This means that a smaller engine with direct-injection can make as much power as a bigger engine without direct injection. By precisely timing and placing the injection of the fuel into the cylinder, engineers have managed to ensure a more efficient combustion. Therefore, it pollutes less too.

However, direct injection isn’t without its critics. “There is a process of getting the technology to not only work but to be durable and cost effective,” Says Brauer. “The latter always takes time when a new technology first enters mainstream production.”
There are many longevity concerns with direct injection equipped engines. For example, the high pressure injection used in these engines causes a lot of stress on the fuel pumps. Regular fuel pumps in non-direct injected applications operate at much lower pressure than the high-pressure fuel pumps in direct-injected power-plants. The difference is in thousands of PSI.

Some high-pressure fuel pumps, like those used with BMW’s twin-turbo direct injection engine in the 2007-2010 335i, the 2008–2010 135i, 535i and X6 xDrive35i, as well as the 2009–2010 Z4 Roadster sDrive35i have been known to fail prematurely.
Another problem with direct injection is with ethanol fuel. Ethanol is known to speed up the corrosion rate of some metals that are used in an engine. With the higher pressure of a direct injection engine, and thanks to the fuel injector being exposed to in-cylinder explosions, there’s a higher chance of a problem or failure. Because of this, it’s more important to use higher quality fuels.
Finally, the biggest concern with direct-injection technology is with carbon buildup. In a direct injection engine, oil droplets tend to get ‘baked’ on the valve. Carbon buildup can create a lot of headaches in the long-term, with build-up being bad enough to make extra noise during operation and damage the engine. At the very least it can reduce fuel mileage, and affect performance.

Direct Injection Could Be Maintenance Nightmare

June 29th, 2011Goto commentsLeave a comment

Cars with direct injection: Trouble waiting to happen?
Writers across the automotive blogosphere are guilty of using the words “direct injected” as an adjective meant to give some punch to the description of a new engine. I am no exception:
Buick will offer a no-extra-cost 3.6-liter direct-injected V6…
But what does “direct injected” really mean? Many readers of this blog are enthusiasts and know exactly what the term describes, but for others, it’s just more techie jargon that sounds cool in front of the term “V6.”
I’ll briefly describe what it means, but more importantly, ask if direct injection is the savior some automakers believe. Some evidence is beginning to crop up that could translate to future maintenance disasters.
First, for the uninitiated:
A direct-injected engine injects pressurized fuel directly into the combustion chamber, rather than into an intake manifold where it gets mixed with air and then enters the combustion chamber.
The results of direct injection are improved fuel economy and cleaner emissions due to a leaner fuel burn, which Ford, GM, Volkswagen, Hyundai and others love to tout in advertisements and press releases.
The problem, though, is pretty dirty.
Auto Observer reports that the issue lies in the tendency of direct-injected engines to build up a layer of carbon around the intake valves that can significantly affect the performance and economy of the engines over time. The dirty grime builds up in a DI engine because, unlike a port-injected engine, there is no constant spray of fuel to keep the deposits washed off the valves.
The repair can be quite expensive, though some guys at a BMW forumswear that “giving the car a good flogging” once in a while burns the deposits off. Maybe… but that’s probably not a substitute for dropping the bucks and having the valves cleaned.
Volkswagen has known about the DI problem for quite some time, saying in a patent application that the carbon deposits can have extremely negative effects on performance.
Owners of Cadillac’s direct-injected V6 have also reportedly started to complain, though GM remains adamant that it has engineered around the problem.
Whether the problem exists only in the Caddy owners’ heads or not, it’s becoming quite clear that direct injection still has some hurdles to clear before automakers roll out the technology across the board.

This article quotes auto maker PR reps claiming "we have no issues with this problem" (they all claim the same) but as the dyno graphs, etc. show the auto makers PR spin has been shown to un-true:

Tony Chick, principal engineer at European Performance Labs in Stratford, Connecticut, has made a career of repairing and rebuilding high-performance engines from Audi, Porsche AG and BMW, among others and his operation has garnered a reputation among car enthusiasts as a go-to place for cleaning DI engines that have become choked with carbon. Chick thinks the problem for most affected engines can be traced to the breathing system – specifically, the design of its crankcase ventilation and exhaust-gas recirculation components.

All modern gasoline engines return some crankcase and exhaust gases back through the intake manifold in order to help control emissions, but, according to Chick, some exhaust-gas recirculation designs are “dirtier" than others. Some, he said, are less-effective at preventing the passage of tiny bits of oil, carbon and other particulates that eventually get baked onto the intake ports and valves.

carbon build up.jpg

Chick reached his conclusion after inspecting dozens of different DI engines at his shop and finding some, like the V8 in Boyadjiev’s Audi RS 4, regularly choked with carbon while others, like the DI version of Porsche’s horizontally opposed 6-cylinder, remained much cleaner.

If he’s right, the rapid adoption of DI has actually illuminated an issue, not caused one. A “dirty” intake or exhaust-recirculation design can easily go undetected in a conventional port-injected engine due to the cleaning effect of gasoline passing over the intake valves. When the same engine designs are adapted to direct-injection fueling, however, that cleaning effect is suddenly lost – and the carbon layers can build.

There is no simple fix for engines that are prone to carbon build-up, Chick says. What’s needed is a complete redesign of the crankcase ventilation and exhaust-gas recirculation systems to prevent particulates from getting through. Fortunately, the manufacturers whose engines are frequently cited in carbon build-up reports – mainly VW, Audi and Lexus – appear to have taken this step with many of their latest models. For instance, Audi’s new 3-liter supercharged V6, used in the S4 and A6 models, has so far been free from carbon-related complaints – a far cry from the 3.2 liter V6, which has numerous threads dedicated to the condition.

If Ford and GM engineers and Chick are correct, the carbon-buildup problem now may be relegated to previous engine designs that were not well-adapted for DI. But that’s probably little consolation to some early adopters like Boyadjiev, who must add regular carbon cleaning services to their cars’ ongoing maintenance requirements – a cost that, for now at least, they are expected to absorb entirely on their own as they grapple with the “dirty” secret of this emerging technology.

Mark Holthoff manages customer support for
Matt Landish oversees digital media development and publishing for

AutoObserver Staff: Mark Holthoff and Matt Landish
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