tdawg183

Hey guys, i've seen posts out there discussing the fact that these cars (S8) can experience carbon buildup in the intake manifold but how many diagnosed cases have we seen? I've seen proof with some S6's but none here.

I ask as unfortunately I had mine in last Monday for a CEL, VCDS detected misfires on cylinders 3,6 and intermittent on others and it in fact was confirmed to be a case of carbon buildup. Needless to say, I asked for them to take pictures and will be able to post soon (sorry).

There was also an oil separator that needed replacing while in there. Any chance that could be a partner in crime to the problem?

The total $ damage wasn't as bad as I thought considering what people said it could cost. I was in/out for less than $2k, parts (including battery) and all at the dealership.

EHLO

Yes, please post pictures when you can.
A malfunctioning Fine Oil Separator could cause carbon buildup on the intake valves and manifold, as it's responsible for returning vaporized oil back into the crankcase.
I'm going to check mine with a borescope, but first would need to remove the back part of the manifold to be able to thread it through the runners.

Jake Musser

In for more info. I have found that my S8 has suffered some HP loss and I can only presume it is caused from this Carbon Build up.

tdawg183

Yeah, according to what I've read that sounds like it could be the culprit. Will update soon once I get the car back (hopefully today).

mishar

Carbon buildup can cause a power lost but I don't see how it can cause misfiring. All that carbon thing reminds me of leaky condos in Vancouver area. There are some of them but it is also excellent source of job/income for some people.

tdawg183

There are definitely a lot of technical articles out there that explain how (and why) misfires can occur due to carbon buildup. Its actually pretty straightforward. Just FYI.

mishar

Can you please post a link to your favorite article on that matter.

Mister Bally

http://en.m.wikipedia.org/wiki/Chevron_Cars
;-)

tdawg183

Sure. and in no particular order:

Engine Misfire Detection by Ionization Current Monitoring
Investigation of the detection of knock and misfire of a spark ignition engine with the ionic current method
A review on biodiesel production, combustion, emissions and performance
Effects of preheating of crude palm oil (CPO) on injection system, performance and emission of a diesel engine

Also, i couldn't find it but i do seem to recall an acknowledgement in an Audi patent somewhere that their FSI engines are prone to carbon deposits. A far cry from BMW which on the other end of the spectrum has outright denied the same.

mishar

I didn't purchase those articles to read all of them, but in abstracts I couldn't find a word relating intake manifold carbon buildups and misfiring. I also did my own search just to find a number of treads like this where people just perpetuate unproved stories.

I am not saying that carbon buildups doesn't exist. As a matter of fact they where more common before, with lower quality fuel and oil. Things got worst when emission laws required recirculation of crankcase vapors through the intake. Any oil that reach intake manifold and valves, either from the crankcase or around valves, will cause buildups. FSI engines are just a bit more prone to that because there is no fuel to dissolve oil.

Carbon buildups interrupt airflow causing power loss. But partially opened throttle is doing just the same and since both are after MAF that doesn't change mixture quality. I don't see any reason for misfiring.

Carbon buildups inside a combustion chamber are a different thing. If they are on the spark plug they will cause misfiring. Those on the cylinder head and pistons will cause detonations or self ignition.