So, I know my Avant needs a carbon cleaning. It's never been done to my knowledge, it was a crusty mf'er when I got it and it had a new block put in...
I know the process inside out from reading tutorials and watching videos on it, and from working on this thing a lot myself, but this keeps gnawing at me.

I don't have a garage, so reducing work time and involvement is always a priority, and while I realize that removing the lower intake runners give far better access and probably a better result, this step is also the most involved and the most cost-incurring in the process.
Can the valves not be cleaned with the lower intake runners in place, by keeping the flaps open and either soda/walnut blasting from there, or using chemicals/picks/scraping? As far as I can tell, the only obstacles are the flaps and the splitters, as seen in this picture:


From the tutorial on this site. Flaps held open.

Leaving the lower runner in place eliminates the need to remove fuel lines, connectors, engine hoist eyelet bracket, saves on injector risk and seal costs, saves on lower runner gasket costs, etc, etc...
So, what am I missing?

- S

 

When I performed a carbon cleaning of my '06 A6 Avant 3.2L V6, I removed the lower intake manifolds as well as the injectors, etc. I didn't use the walnut blasting system for carbon removal. But you should remove the lower intakes to gain access to the diverter plates that will also have carbon on them. Additionally, you run the risk of damaging the lower intakes, which are sold as an assembly, doing the service.

 

Yeah, I can see how it'd be risky to go in there with tools and chemicals with the lower runners in place, but I'm planning to use soda or walnut shell blasting to clean. That way, the splitter plates would also be cleaned in situ.
But I can't find anyone who's done it, and I don't understand why? Aside from the risk of damaging something if you stick tools down there w/ the lower runners on... I only see benefits? It just feels like someone smarter than me would have tried it already, or ruled it out for some reason I'm not seeing.

- S

 

Okay, an update on this.
Finally got around to taking the intake manifold off – a much smaller job than some "tutorials" make it out to be... and cleaning the valves w/o removing the lower runners is an even better option than expected.

I used a vacuum pump to get the flaps all the way open, and then zip tied the thingamajig that opens them, so they just sat like that. In this position, the flaps are flush with the sides of the runners, no gap that I could see with my eyes OR a scope, and visibility is excellent.
I wasn't too hopeful so I didn't have my blasting stuff prepared, but I cleaned out (at least somewhat) 4/6 pairs with some brakeleen and the zip-ties-and-drill trick. Turned out reasonably well, for the effort I put in. This would be the riskier way to do it IMO, regarding potential damage to things, but that's also the case w/ lower runners removed.

Dividers also turned out pretty good, just left in place. They would be even better if blasting with soda or walnut, and the standard "tool" with a hole for a shop-vac and blasting wand also fits perfectly snug on top of the upper runners.
I plan to take the manifold off again and do it properly with my soda blaster when I get some free time this summer. And I won't be removing the runners. IMO, the only reason to remove the lower intake runners, would be if there's a problem with the flaps, and you can't zip tie them open.

As far as I can tell, my hypothesis was correct - quicker job, FAR less risk to components, FAR lower cost when not having to replace seals etc. for lower runners and injectors, and FAR friendlier to newbies or first-timers.

Come at me.

- S

 

Like your spirit of innovation! Would be cool to hear how well walnut blasting works with this approach. I’d be concerned the wells would just fill up quickly and prevent proper cleaning.

 

Thanks!
I'll update when I get around to using blasting media.

I did try putting the little cap for the blasting process on top of the runners and used my blow gun to check airflow, and it seems to flow well back out. With the divider in place and in the way, filling it up could still become a bigger issue than with the lower runners removed, but I'll report back.

- S

 

If I'm not too late, I'd recommend you do not do this. Using a walnut blaster will destroy your lower intakes. I tried this with the lower intakes removed for less than a second at limited pressure and walnut ate the plastic badly. Besides, with the dividers still in place, you won't be able to properly see the valves and seats to ensure proper port closure before introducing anything in there. Failing to properly shut the ports will lead to compromised catalytic converters. I advise you follow the proper procedure and remove everything. Many clear views and angles in my detailed video below will make you realize this is not a good idea.

 

Hey!
I've watched both your videos on carbon cleaning quite some time ago, and there's a lot of good info in there!

After experimenting with the lower runners in place using the Audi recommended "bunch-of-strip-ties" method, I think visibility of the valves is quite good with the runners in place. Shadows are the biggest issue and good lighting solved that for me - line of sight is hardly obstructed at all.
Before doing anything, I tested that the valves were actually closed by syringing some gas into each, and making sure. The two that were open, were also very clearly visibly open.

You've a good point about the walnut - it's clearly quite an aggressive medium for plastic. My plan is to use soda blasting instead, and having tested it on comparable plastic, I don't think it should be a problem. Since it's far less aggressive, it'll take a little longer but be that much safer.
I do think it's a little discouraging that removing the lower runners with all its inherent risks to expensive components, time requirements as well as the cost of resealing both the injectors and the lower runners is described as the "proper procedure". For us "shadetree mechanics", I think finding solutions that work w/o unnecessary risks and the lowest cost possible, should be the priority.

In my case, the carbon cleaning has clearly never been done. Conditions in there could be better and they could be worse, but this should very clearly be done at least every 10k miles or 15k kilometers or so, and at the very least as a regular maintenance method for low and softer carbon buildup, this is clearly, clearly preferrable over "removing everything", as you say.
Intake manifold off, drill, carb cleaner and some strips and you're good to go. Upper intake manifold gaskets on mine looked a little tired and crusty so I replaced them, but they don't need to be replaced every time. Making this an easy, cheap and accessible procedure for pretty much anyone.

- S

 

I understand and I wish you good luck.

 

Late to the party, but I’ve noticed some owners getting decent results by scoping the valves first to see how bad the buildup actually is. Has anyone here tried doing a quick borescope check before deciding on a full teardown? It might help figure out whether a light chemical clean could buy some time or if it’s already at the walnut-blasting stage.