allenst

to see if I could 'clean carbon'.

replaced air filter and cleaned maf. i have a new maf coming but though i'd clean it since it was open.
decided to try spraying water in throttle at 2000rpm as many suggest it helps remove and clean carbon.
spray until near stall, they say.
i couldnt get it to near stall.
got someone to rev at 3000rpm.
sprayed a lot of water in there and it just seemed to get burnt and sent out ehaust
put 2 towels down under exhaust. no smoke and no black drips.

i have my doubts about this cleaning method for this 04 a8l.
will not do this procedure again

Jack88

I'm always very apprehensive about DIY tricks like that, especially on modern cars. I don't have the engineering knowledge to be sure something isn't at risk. Who gave you that idea? I've heard of using other substances for the same effect, but I'd never try any of them without confirmation from a reputable source that it's alright.

mattsimis

Sounds like poor mans water-meth injection. But with real water injection they use mixes of water and meth (or just windscreen washer) and spray it at super high pressures so its a very fine mist. And of course its done when driving, not just for 20min when stationary.

allenst

its all over youtube when searching "carbon removal"
trust me I read a lot about the potential damage.
there is little potential damage other than inputting too much water but that would be difficult with a spray bottle.

anyway, it seemed like a waste of time imo

allenst

https://www.youtube.com/results?sear...arbon+cleaning

dvs_dave

But if a waste of time on a non direct injection engine as they don't suffer from carbon buildup in the intake anyways. And if you're going to do this, why not use something that is vaguely proven like seafoam?

raj99

As previously mentioned, this is a complete waste of time for non direct injection engines. Furthermore, seafoam isn't much good once you have carbon, consider it more of a very poor man's substitute for such cleaning, since it only gets a small portion of the valves. I wrote about this extensively on the C6 forum, but here's the jist of it.

One of the ways that is identified to removing carbon in a direct injection engine is giving it an Italian tune-up; essentially where the engine is run at full load for extended periods in order to burn carbon buildup. So you have an excuse for a track-day or two

Also, the only way you know if you have carbon, is by taking off your manifold, so it would be near impossible to tell the extent of the carbon build-up you have. The simple fact is that all direct injection engines (what Audi calls FSI) will have carbon build-up and things that have a direct impact on carbon deposits are:

- Fuel quality: The crappier the fuel, the more impurities and the more likely there are to be deposits to collect - go to Top Tier Gasoline for more info
- Driving distance/engine temps: Those hit hardest are short distance driving, where the engine never gets up to temp. Getting the engine hot means that the gunk won’t be able to collect as readily, because it’s baked off by the high temps.
- Poor seating of the cylinder rings: More oil seeps by into the fuel adding to the large amounts of particles recirculated into the intakes. Use of more than 1Qt of oil every 5K miles means higher than average oil consumption usually meaning poorly seated rings, causing excessive blow-by

DI engines (Audi calls them FSI) is really great for making the fuel/air mix ratios and concentrations perfect, it takes less fuel to make the right mix with DI, it takes less fuel to get the same power using DI, and it can also fight knock (pre-ignition, which harms engines) since every injector can operate independently – allowing the ECU to control the fuel to every cylinder individually. It is also used if the engine gets too hot and the coolant cannot keep up by purposefully putting extra fuel in which will evaporate harmlessly but take heat with it. Here comes the con(s).

Non-DI engines have the injectors in the intake channels, and spray the intake valve’s backing as it opens into the cylinder. This happens with each intake stroke, “washing” the intake valve with fuel. You have, I am sure, seen the Chevron with Techron and like commercials about it having additives which keep valves clean. This is great for NON-DI engines. Why the valves need cleaning is due to 1970’s legislation to handle pollution. Exhaust Gas Recirculation (EGR) and Positive Crankcase Ventilation (PCV) are 2 things required by law in the US (and many other countries) to prevent pollution. EGR pipes unburned fuel and particles in the exhaust, back into the crankcase to prevent catalytic convertor congestion and failure (things like unburned fuel, impurities in the fuel, water vapor, CO2, and oil). PCV takes crankcase vapors (mainly just oil particles and the EGR stuff) which is under pressure and pre-1970’s was just vented to the atmosphere, but now is redirected through a valve system which has a rough collection system that attempts to pull the largest particles from the air in this, and separate them out and allow them to drip down into the oil filter to be collected (if bad) or allowed to be cleaned and returned to the oil pan for engine lubrication – the particles too small to collect are mixed with fresh air coming into the engine just above the intake valves and shot back into the engine to attempt to re-burn them properly.

As you can imagine, the particles will collect on all parts of the intake, turning into sludge eventually and oozing into the intake, where it eventually is burned away during combustion. The problem happens with DI engines – the injectors shoot fuel DIRECTLY into the cylinders and don’t wash this gunk off the back of the intake valves. As such the gunk builds up here but since it’s so close to the cylinder, the heat bakes the gunk into carbon deposits which build up slowly over time. These deposits eventually become so heavy that they affect the airflow into the cylinders, making them move in unexpected patterns, or in very bad cases, not enough air is pulled in as the ECU is expecting, either way the result is too much fuel to the air ratio, or uneven mixing of the fuel, which robs engine power, can cause rough idle, and eventually cause Check Engine Lights (CEL’s) due to misfires (especially when the engine is cold). This causes a negative spiral, where the even higher amounts of unburned fuel due to the Carbon Build-up (CB) makes even more unburned fuel be re-circulated and these richer deposits speed the buildup on the backs of the valves further.

A few things are done by people to correct this.
- Carbon Cleaning – the top of the engine is pulled apart, intakes and valve covers are pulled, and the heads removed, then a Dremel or similar tool is used with a fine grain grinding bit are used to grind the carbon off the intake runners, the intake air flaps, and the backs of the valves. This is usually done around every 30K miles by those wanting to be sure they have the power and performance of the car unaffected.

- Catch Can – This is a 3rd party development, which partially bypasses the EPA mandated pollution measures mentioned above. It basically goes in-line with the recirculation of the gases before they hit the intake, comprising of a separate filter system that more aggressively captures and holds the particles the stock system doesn’t handle. The difference here is that the aftermarket solution doesn’t drop this into the oil, it holds it in the can, and you have a drain at the bottom where every 5-7K miles it needs emptying. Due to this being “bad stuff” from inside the engine, it cannot be disposed of easily, and is best poured into old oil containers and taken to a recycling place like Schuck’s or your local recycling transfer station, it’s mainly oil, water and fuel, so it can go into oil recycling.

- Methanol Injection – Typically referred to as “Meth” it’s been around a LOT longer than the illicit drug, and is basically a raw form of octane. What it’s used for is to both cool the incoming air (making it denser and therefore holds more oxygen for combustion) as well as boost the octane rating, which equates to more power. Methanol is mixed 50/50 with distilled water, and uses a special tank to hold it in, with its own pump and delivery system. The methanol is injected into the air intake around the throttle body, misting the incoming air. The methanol mist in the air cools it through evaporation, and since it’s a combustible liquid, it helps take place of the washing that non-DI engines get, by coating the backs of the valves and pulls the deposits into the fuel system rather than it baking and hardening there, as well as giving more horsepower and performance out of the car at the same time. Methanol is not very expensive, but is dangerous due to high octane and ability to burn, hence mixing 50/50. A typical use system will go through a small (1 liter) tank every 1-2 tanks of gas.

One of the things I didn’t mention (as it didn’t pertain to your car) is that Forced Induction (FI) engines are not as susceptible to this, the reason being the much higher compression and thus higher cylinder and valve temps if you do get it out and run it for at least 10-20 minutes at normal running temps.

mishar

I know why this doesn't work, but I may be wrong. So can you explain how that exactly work?

dvs_dave

I think the Italian tune up will help keep on top of light deposits. However once it's caked on, manual cleaning is the only option.

I think the theory is like your pyrolytic oven (aka self cleaning) at home. It essentially gets everything hot enough to turn the greasy oily baked on deposits into ash which then gets blown away by the intake port airflow. A sound theory but in practice I doubt the inlet valves would ever get hot enough for long enough for this to actually work outside of a sustained track, dyno or autobahn session.

MP4.2+6.0

Was your C6 a 3.2? FWIW, I think of those (from the Q5) as being ground zero of the carbon issues. I feel bad when I see a Q5 owner with a 3.2 post about a problem, or even worse when someone posts about buying one with the board populated by some 3.2 owners still. I just keep my mouth shut there in general. Some of the Audi motors had a convoluted head design that could apparently put the residue crap on the exhaust side too; I think the 3.2 may have been prime among them? Thus, I think the fouling issue varies with the exact head design. Even among the 4.2's it seems to vary, and again there are a couple of 4.2 FSI designs--the broader torquer curve less peaky one like the A8 and the peaky one for the RS4, R8, etc. S4 where I sense more fouling discussion probably had the first design, but it may also have some different style drivers in general. Among the motors some seem mostly poorly designed oil vapor systems (especially for the cold oil and water mix), but others may overlap into the air injection + EGR set ups. The latter gets to the more difficult scenarios since it isn't just an intake pull to clean valves worst case; you mention pulling the head for cleaning, but again that's primary for the designs that foul the exhaust side or ports too; many aren't known for that.

For what it's worth, I own another of the ground zero direct injection fouling motors, the Mini S second gen Prinz motor. BMW quietly tried to redesign the oil vapor system several times, presumably dealing with fouling. Forced induction BTW as far as that theory, and arguably the Mini/Prinz turbo is the most widely known fouler. For that matter, Audi's 2.0T in early versions is known as more of a fouler than the 4.2, and IIRC also got the Audi extended warranty for cleaning. With the Mini the accepted easy fix is Seafoam as another poster mentioned; enthusiasts do catch cans sometimes, sold as specific kits for the make. I did the Seafoam personally when it got afflicted at about 30K miles. The "before" cold diesel knock type noise that motor comes down with compared to the "after" normal running sounds was night and day.

Back on the OP, from having had blown head gaskets several times back on the early 70's C1 100LS lemon motor--later modified for the 924, AMC Pacer and Gremlin--I can confirm that over time water (steam at compression temps) does a very good job of "steam cleaning" a cylinder. Those were old sloppy cast iron blocks with very loose tolerances and that burned some oil including through the (pre PCV) screen only system they had for vapor control. When I tore the heads down if it connected to a bad head gasket pull, that cylinder's valve stem area was also a good amount cleaner, as was both the piston crown and the (flat) aluminum head area inside the cylinder diameter. But that was often days or more of running before seeing the steam cloud out the exhaust or tracking down the coolant loss; they rarely blew from the water to the oil.