Direct injection is all the rage right now, but I was surprised to learn that there seems to be some issues with it. A friend of mine has one of the newer turbo BMW 335i’s that use direct injection and he was asking me if there was anything that he could do to clean the deposits off of the intake valves. This was a surprise to me since I have rebuilt port injected engines that had high miles on them, and the valves looked very clean. To show what he was talking about, he sent me this link:
The problem seems to be that since no fuel ever touches the valves like in a port injected engine, the valves never get ‘washed’ and are thus left to grow these deposits. This happens even with very low miles on the engine. This is further compounded on my friends turbo car which has a lot of pressure in the crank case from blow-by, which then pushes oil through the PCV system into the intake. This is why the buildup on the BMW valves in the pictures are so big. The problem is also not unique to BMW: Audi and even Ecotec owners are complaining of a similar situation.
I find it strange that somehow during development and testing of these engines, the engineers were ok with this? They must have run into this problem in the lab!
6 Comments to "Direct injection and dirty intake valves"
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Well there is going to be a natural build up of carbon and oil in the engine over time. Though what needs to be taken into account IMO is the fact that e85 is also being used in fuels. Ethanol, and other cellulose fuels can cause a gum up in the valve train. I would especially be concerned with the blow by though…. To me it seems like the rings on the pistons never set correctly or weren’t sized properly. Granted turbo cars seem to burn a little bit more oil that their naturally aspirated cousins, but that is a ridiculous amount of build up.
What I would like to know is if these people are driving these cars solely around city streets, driving with spirited intentions, or are taking them to the track. I also think that the PCV system is a big part of the problem.
There have apparently been some people who have vented their PCV systems to the atmosphere with a catch can to collect any oil; this seem to prevent the problem. The engines pictured were also running more boost than stock – so that is causing more blow by than usual; but still, it should never lead to build up like this and I’m sure this happens at OEM boost levels. I’m just shocked that the manufacturers are OK with engines that do this. It seems like the technology isn’t quite ready for prime time…
I would like to know where you got your information from on Ethanol. Pretty much all of ethanol fuel, including the 15% that’s E-85 is derived from corn. Cellulosic ethanol, made from grass, corn stalks and other non-edible bio mass is not really in production and is still being studied. As far as I know, there is only one facility producing cellulosic ethanol. There is also no chemical difference between ethanol derived from corn or cellulose, both will get you dunk! If there was a difference, it wouldn’t be ethanol.
Alcohol fuels (both ethanol and methanol) are very clean burning when compared to gasoline and leave less deposits. Alcohol is also a very powerful solvent and can actually clean your engine, it is also an ingredient in brake cleaner and I’m sure you know how well that works at cleaning stuff. I think where people get the idea that it can gum things up is when older gas cars have an alcoholic fuel put in them. The alcohol breaks up any varnish or deposits and that clog things. One of the problems with alcohol is that it is corrosive and attracts water, both not good for the steel in your fuel system and engine. So that pitting and buildup on intake valves on an engine that runs alcohol is probably corrosion…
Here is what I am talking about (glad I book marked these from a long time ago):
And about half way down:
It seems that this happened really early on as they were still trying to get the detergents figured out because I was doing some searches just now and can’t find anything in the last couple of years. So my fault for not having checked recent history and writing the post before I had my second cup of coffee. Anyways it was more of a problem in standard engines. But with DI this wouldn’t be an issue anymore since the fuel is being put directly into the chamber. I would suggest to your friend getting a can of seafoam and running it through the intake to try and see if that makes a difference. Oh and put that catch can on the PCV port. I think I remember seeing something similar happen on my friends old SN95 Mustang (too many models of this car so I hope I got it right), he did the catch can method and problem solved.
As for cellulosic fuels, Corvette Racing has been running E85 in the GT2 class on cellulosic fuels so far this season. It will just take time for it to come into full fledged production, especially since they do cut down on emissions more so that corn derived ethanol. That or the government will want to make us all have electric cars (NO THANK YOU!).
I would say that DI is doing exactly what it was designed to do: extend fuel economy. It does that pretty well too. You may also remember that the N54 engines from BMW have had a bit of rough service life so far. It wouldn’t surprise me (and this comes from a guy who has owned two different BMW’s) if it is something that BMW didn’t get right….
I’m not sure, but my initial thought was along the lines of what you said about alcohols being a powerful solvent. Wouldn’t a water-methanol injection system help keep the valves clean among other things?
Yes, it would help keep the intake valves clean.
I think the intake valves carbon up because of the lack of a wet intake. Port injection helps keep the back side of the intake valves clean as the engine is running. Sure, eventually a small deposit or so may form due to PCV problems or bad valve guides in engines with many miles on them. GDI engines don’t spray anything onto the valve so there is no cleaning benefit. I think intake port velocity has something to do with this phenomenon. If airflow slows down, the air and oil mixture (oil from the crankcase vapors and blow by) has time to burn onto the back side of the valve. This problem would magnify itself in cars that are “granny driven”.
I don’t know what the solution is, however it seems that the manufacturers only care about making the car last through the warranty period. Most of the GDI cars can make it 3/36 or 5/50 before the engine wont run properly due to restricted intake flow.
In our ’13 Hyundai Sonata, I noticed that the oil turns black after 2-3,000 miles. It seems that the very fine spray from the GDI system makes its way past the rings perhaps and fuel contaminates the oil prematurely. The car runs great, but I do change the oil every 3-3,500 miles.
I don’t think Seafoaming or intake soaking will work. Have you ever tried to scrape off those deposits on a valve? From experience it is damn near impossible without a wire wheel. I’d like to see a product, or invention to minimize these deposits, or else owners are looking at a top end job every 60k or so, just to keep the valves clean.