Stoney

Our A4 1.8T (1997) was running rough, so we took it to Anderson-Behel in San Jose. Service Manager George said everything was fine except a lot of carbon buildup. They are going to flush it out (costs about $130).

George felt that the oxygenated gas in California was to blame. I asked about Chevron with Techron versus Union (which was primarily used in the A4), both of which are supposed to fight deposits. George said that it really wasn't enough to fight the effects of oxygenated gas. Does this make sense?

He suggested an additive made by "Marvel Mystery Oil". Add a can to a tank of fuel. Add 1" from a bottle to the oil just before an oil change. Does anyone know about these, or about other additives?

JP4

what I would do is get the Chevron/Techron Concentrate in the 20oz. bottle and put THAT in your tank before a fill-up. I'm pretty confident that it will make a differance for you. You'll have a much higher concentration of Techron in the tank for that particular tank full. I use a bottle of it between each oil change on the 4.2 and my wife's urban assualt vehicle (Grand Cherokee)! If I'm late with an application of it on the Grand Cherokee it will start pre-detonation pinging pretty quick from the deposits that form in the engine.

Auto Union Jack

There was a Porsche tech Bulletin advocating Techron additives in the early 90's.

quattro5

i even have a can lying around, can't remember why exactly...

just as a layman, it's oily and doesn't seem like it would be a very good solvent for carbon build-up. i've heard it has stoddard's solvent in it though, maybe that's what does it? it does have nifty red dye in it so it looks cool.

Seattle Scott

Marvel Mystery oil used to have a really good valid purpose in life which I have forgotten. I understand Turtle Wax owns them now. Comparing wax with fuel additives probably isn't smart but I'll do it anyway. The wax is crap, Marvel Mystery gas treatment is probably crap too.

<img src="http://www.turtlewax.com/products/img/performance/marvelgas.jpg">

Muhammad did some research and found the good stuff which is held in pretty high regard on the Internet at least. This isn't for monthly use. What are you looking for? An additive to add once a month or something to blow carbon away evry few years?

Picture Courtesy of Muhammad :

<img src="http://pictureposter.audiworld.com/153/bg44k.jpg">

Arburg2.7t

It seams to work very well. I have also talked to people who love Sea-Foam. They say for carbon deposits just pour it in through a vacuum line untill the engine stops and let it sit overnight, start it up in the morning to clear it out.

I have not tried it yet, but I might on the Grand Cherokee first

Muhammad

BG is much more expensive ($25/bottle vs $6/bottle). I run it once in a while... some people run a bottle of Techron every month just to keep things clean, so to speak.

JP4

Interesting...I think I'll stick to the Techron Concentrate though! ;-)

Suds

Just thought I'd share some of my experiences on this subject:

The best way to get rid of carbon deposits is to use a fuel system cleaner kit designed for professionals that connects to the engine through the fuel rail. Nothing beats this. I do this on all my family's car every six months and the results are astounding.

This is the same as the $80-$130 treatment that is performed by independent shops or dealers but ends up costing much less. (A can of cleaner costs between 12 and 20 dollars). Thus, I can afford to do it every six months. There is an added benefit of doing it every six months as opposed to every few years when the idle turns rough and power is lost gradually. After a year or more, the carbon deposits are pretty much baked in and require repeated flushes to clean up even partially.

Chevron is definitely the best gas to use for minimizing carbon problems. I say this not because of their Techron ads but because I have personally seen (or own) Mazda, Nissan and BMW manuals or Technical Service Bulletins that recommend Chevron. Having said that, there is only so much that Chevron can do. Injector and combustion chamber buildup is caused by hot soak during engine shutoff and the Techron cannot prevent that. It burns cleaner but is limited in its ability to actually remove deposits since it is diluted with the actual fuel. The worse the deposits, the more powerful the solvent must be to remove them. This is why Chevron and other companies sell Techron packaged as "total fuel system cleanup" and recommend adding a 20 oz. can to the fuel tank every 3 months. Note that it is NOT wise to add Techron concentrate at every fill-up as it is pretty powerful and can deteriorate fuel system components over time.

But even this method does not remove stubborn deposits since the 20 oz of Techron is still dilute by 17 gallons of gas. Not to mention that I have not seen any improvement in power in my brother-in-law's Mazda Protege (used to be mine) before and after adding Techron concentrate, whereas with a professional flush, the difference was dramatic.

So what's the professional flush? It consists of supplying a powerful solvent (like Techron) directly to the engine by disabling the fuel supply at the fuel rail and connecting the solvent to the intake line. The engine then runs on this special solvent for 15 minutes or so and the deposits are heavily reduced (never eliminated, sadly...) The fuel pressure regulator must be disabled to prevent extra solvent from returning to the fuel tank as it is very corrosive (even Techron concentrate must be added to a full tank only).

To get the 40-55 psi that a fuel-injected engine needs implies that the solvent must be pressurized. Accordingly, manufacturers of these kits have two ways to achieve this -- pressurized aerosols and pure liquid solvent that needs an air compressor to pump the solvent to the intake line. Both were equally effective in my tests -- the aerosol method does not need a compressor but also wastes some solvent (plus the can) every time, so professional shops almost always use the liquid solvent method.

There is a third method (the one used by most Audi dealers because they get the equipment free) and that is to apply a fine mist of the solvent through the air intake system. To my knowledge, only two companies even offer this third system (Wynn's oil company, which Audi recommends and provides to its dealers and 3M -- both are on the web if you want more info.) IMHO, this system is not as good as the fuel rail methods but is a lot easier to perform as engine vacuum does a lot of the work for you. It does have one advantage and that is that the engine top-end (air intake, throttle body etc.) also get cleaned quite well. It does not do a good job on injector deposits but does a decent job on carbon deposits in the cylinder. ( I visited Wynn's oil last week when I was in LA!)

The best equipment is made by 3M but is a little pricey. Hence I sold mine to a professional shop and went for NAPA's system, made for them by Borg Warner. (also on the web, search for Cleen Plan).
However, in my tests, 3M's chemicals performed much better than anything else. In fact, 3M is the only company I know that has two types of chemicals -- one for injector sludge and one for cylinder carbon deposits. It is also the brand that gives me the best power improvement in a before/after comparison. Both equipment and chemicals are also supplied by big name comapnies like OTC and Snap-On.

The procedure is particularly easy to do on an Audi because the fuel rail fitting has a threaded 14mm connection that is right on top of the engine and easy to tap into. It is also easy to disable the fuel tank simply by pulling a fuse.

If anybody in the Bay Area would like to do this, I'll be happy to get them started... let me know!

If you do want to go the additive route, I would recommend using this:

Autobahn Gasoline Additive:
Audi part number ZVW 239 003

as it has been tested by Audi and will not harm your oxygen sensor or other emission components and is formulated expressly for this purpose. (All the brands I mentioned are "safe" -- I don't know if the same can be said for Marvel!)

Also, to reduce sludge and varnish build-up in the engine bottom-end and lubrication system, I use Lubro Moly Oil Sludge Remover every other oil change. (available from www.automotion.com). Lubro Moly is a German company and their products are TUV approved as well as tested by the Big 3 German carmakers. They also have some excellent additives for intake valve and injector cleaning but I don't need or use them since the "professional" flush does a far better job on those parts than any additive can. Again, I know this stuff works because I compared it by pulling the oil pan on my Audi and inspecting the interior!

Also, I have heard a lot about BG44K on this forum and plan to try that next... I do know that so far, no additive has provided that huge boost in power and smoothness that I see after a proper "on-car flush".

Stoney

Thanks for the details and many alternatives. I'd like to learn how to do this, living with CA gas!