Carbon build-up in DI engines
 

Seems to have found the actual cause, and catch cans and meth really don't work…

Turbo Fuel Stratified Injection (TFSI) & Direct Port Injection Carbon Build-up Problem | Oilem - Lifting the lid on the market

Thats why I won't buy a car with DI till the figure it out...

Good informative article. Thanks for sharing as I was not aware of this issue.

This is a problem for the GTi I own but its not a world ending problem. The RS4's of Audi in 2006 etc had major problems as well as the early R8 4.2's. If you have a Mk6 GTi like I do you will need to clean this around 60-100k miles. Sucks overall but its not that big a deal. There are ways to mitigate this by driving with higher revs occasionally but nothing can prevent it at all. Seafoam nothing.
Quite a few cars are affected but changes to injection design have been made especially by VW to prevent this.

As DLSTR said, this is definitely an issue with the GTI platform (I had it in mine). The only way that I've found, by researching it, to avoid the build up was to really get on it. VW actually recommends driving their DI cars above 3k for long periods of time (at least 20 minutes) each time you drive the car to help avoid buildup. There are many people I know who will actually stay in 5th vs 6th on the highway to work to help keep it down. Problem is that once you get that build up, you're pretty much stuck and need to clean the valves. As weird as it sounds, CLR worked wonders with really pulling that build up off.

Essentially if you go DI, just make sure you actually drive it like it should be driven and that should keep you from having to do valve cleanings for longer periods of time.

Sorry officer. I was just cleaning my valves...

For a long time Audi and VW said there was not a problem and did not want to cover it under warranty. So the guys that popped 80K for a RS4 had to pay for valve cleaning on their own. Audi did some crappy BG induction service and a ECU reflash that failed miserably. To me spending that amount of money on a car and it not being covered, is why I'm out of the Audi scene.

The reason they won't cover it is because it is "normal maintenance" that is supposed to happen on the vehicle

Diesels have been direct injected right from the start. Why do they not see this sort of thing happening? Its the same systems (EGR, PCV) on both engines.

Water injection could be used to keep them clean no?

The Bimmer world uses Walnut blasting.

REVIEW: Cleaning of intake valves with BMW walnut shell blasting tool

I think it might have something to do with the way you are supposed to drive a diesel. I believe you are supposed to be driving them at high RPMs from the very beginning of their life, which is going to keep the carbon build up to a minimum is done properly

I may be misinformed on that though

You got it backwards. Modern pickup diesels like to run anywhere from 1600rpm to 2200rpm. Most red line or have rev limters around 3500rpm.

Thinking about this after I posted it thought it could have something to do with the higher boost keeping the gunk from sticking. Mind you at cruise a diesel only sits around 2-5PSI.

I guess that would make sense. I didn't really know about the truck aspect of it, but was thinking about it from the point of view of smaller diesels (ie. Golf TDI).

Never owned a diesel so I don't really have a huge abundance of knowledge with them.

Im just curious as to what causes this to be an issue here but yet you can have a diesel with 500K miles and the valves will look ok (not good, but not coated like that picture by any means). Maybe there ports are designed in such a way to speed up the air entering the cylinder so that the air moves much faster around the valve? I know for a fact that the EGR systems on a diesel are way way more messy than that of a gas engine. All that soot goes into the intake tract. If you could find the difference between the two I think you would be well on your way to a solution. For all we know it could even just be a special coating on the valves.

Looking around it seems like there are a few things with the Diesel direct injection that are interesting. Apparently the biggest issue facing those engines is idling. The recommendation (and this may explain why cummins drivers seem like d-bags all the time), is that to combat the build up in diesel engines you should floor it 10-15 times a drive. Apparently the way that the EGR is setup, it closes during full fuelling which means that flooring it should blast away all the crud and gunk. It doesn't seem like the Gas Direct Injection has that same setup on them. It looks like the smaller displacement turbo cars should have an easier time avoiding carbon buildup because they are more likely under heavy load for longer periods of time.

This is the inherent issue with DI, my previous platform the Mazdaspeed was DI also.

Thats not entirely true. I have seen the inside of diesel engines on farm trucks driven by old farmers with nothing out of the ordinary in terms of build up. I mean you always will have some but nothing to affect performance a noticeable amount or anything like that. Surely nothing like that picture. I suggest deleting the external EGR where ever possible, its just not a good setup. Most new cars just have a internal EGR by changing the cam degrees with respect to each other.

I bet if there was a way to turn this off on the Z you would see both fuel mileage and power gains from it. The Z does not have external EGR system on it, so it only leads me to believe it is controlled by the VVEL.