Topic: carbon buildup on intake valve

[rich71]

I was on the other forum and this topic popped up. Seems interesting about di intake valve carbon buildup - has anyone had theirs torn down and noticed this? - i copied some stuff from the other site, hope that is ok.


Quote:
It seems as though more and more cases are popping up where direct injected engines are experiencing miss-fires, rough running, and reduced power output due to extreme levels of carbon buildup on the intake valves. Audi's 4.2 FSI V8 and 5.2 FSI V10, VW's 2.0T, and Porsche's 4.8 DFI V8 are known victims so far...

Presumably, this is because normal port-injected engines have the added benefit of washing away any deposits that may form with the fuel spray. Unfortunately direct injected engines have no way of clearing off deposits and thus need to go in periodically to have the valves cleaned.

Is this a design flaw with direct injection or is there a solution on the horizon? Has anyone had first-hand experience with this phenomenon? 

Links for reference:

http://forums.audiworld.com/showthread.php?t=2746852&highlight=carbon+build

http://www.planetporsche.net/cayman-chat/32256-maybe-dfi-not-good-buy.html

[lil goat]

I have no experience but the first thing that comes to mind is how the cars with the problem are being driven. If you drive and NA to easy and not like you stole it, you know 4 grand shifts, 5th gear by 45 they will clog the cat is no time, been several instances of this reported. I would think driving the crap out of it and doing 7000rpm shifts would keep things pretty clean. I also run top tier gas maybe that helps maybe not.

[AdamVIP]

I dont think your fuel quality will help this problem if it exists in our motors.  I think the problem is because is DI no fuel ever flows over the valve so cleaners never hit them. I think the only way to clean the valves would be to manually do it.  

I would think that we would have seen this many times over if it was a problem with the LNF.  People have run up quite a few miles and I havent heard of this.

[Mac]

you might be able to View it from a a spark plug hole. no need to open it up. well there are alot of lnf.s out there as test cars.

[tazz]

Could one introduce Seafoam into the intake and would clean that right up.

[rich71]

there is someone on the other site that is rebuilding the heads with different valves so i popped off a question as to if he has seen any carbon on the valves. I too would think it would be know by now if it was something we could get.  If you just putput around town i could see buildup occuring, but my car sees high rpm shifting everytime i drive it so i would assume the carbon, if any, goes bye bye out the pipe.

[Sol Asylum]

Here is something to ponder.  If all that is passing by the intake valve is air then where is the carbon coming from?  Don't give me any of that global warming carbon foot print crap either.  The amount of carbon in the air we breath would not be sufficient to cause large carbon deposits to build on the valves.

when I used to do top overhauls on aircraft engines the intake valves always had more carbon on the valve stems then any where else and most of the time it was because the guides where allowing oil to run past.

[tazz]

My guess it has something to do with the design of the PCV system because of emissions standards.  Oil laden air is being recirculated through the intake system thus causing the issue.
Take for instances my SuperCharged Ford truck.  On that vehicle boost doesn't cause the problem but the negative pressure that occurs right after you let off the gas causes oil laden air to be sucked into the intake before the SC into the TB and also through another inlet on the SC side.  The oil laden air will coat the TB and the SC rotors as well as the inner cooler where the air charged is cooled down right before in enters the intake runners to the combustion chambers.  Pics of people who have removed there SC to expose the innercooler show alot of oil.
The Solstice I hope has a better design than the 5.4L Ford modular in that I suspect that it does have some sort of factory oil separator to prevent this from occurring or maybe minimizing the issue or maybe this problem is not as pronounced with a turbocharger vs Supercharger.  In any case since the fuel air mix is not touching the valve tops because of the Direct Injection fuel system the oil that may be present in the air collects on the valves.  The detergents in the fuel actually probably clean the valves and in a sense wash away the crap before it really gets a chance collect and form deposits in a port or multi point fuel injection system.
Just a theory though on what may be happenning but it does make sense.

[tazz]

Here are some pics on what I have to deal with in my Ford if I do not have some sort of aftermarket oil seperator installedat just 30K.

[tazz]

What there supposed to look like.

[Sol Asylum]

I would have to agree with you that the carbon source would be oil.  However the fuel that would pass an intake valve in a non direct injected engine should be in a gas state ie its been vaporized therefore how much "washing" can it do?  But this would be a different topic all together.

The question at hand here is carbon fouling of the valve and it would seem that the cause would be oil that is getting into the intake by whatever means.  So do the cars that have direct injection and an issue with carbon fouled valves also have an issue with excess oil consumption?  I haven't noticed my Kappa loosing oil but then I haven't driven nearly the miles that others have.

[tazz]

What is consider excessive useage for our Sol though?
1/2 qt in 5K?  More or Less than that?
Just trowing out a # to give an example to better understand what would be considered excessive oil usage.

[rich71]

could it also be caused by overlap? The vvt constantly adjusts this correct? 

[Sol Asylum]

I kind of doubt that valve overlap with a forced induction engine will cause this.  The intake valve will be opening just before the exhaust valve closes meaning there will be very little exhaust gas pressure still in the cylinder where as the intake air will be under pressure therefore no exhaust gas will be able to back feed into the intake port.

[LiquidPT]

I would have to agree with you that the carbon source would be oil.  However the fuel that would pass an intake valve in a non direct injected engine should be in a gas state ie its been vaporized therefore how much "washing" can it do?  But this would be a different topic all together.

Ah, but it's not in a gas state... it's atomized in the air...

Think of a humid day. The water in the air isn't in a gas state... that would require it to be over 212F to make steam. The water is just in sufficiently small droplets to be suspended in the air.

Same thing with gasoline in intake air (non-DI).

[snaponbob]

Time out, folks. So far, it's a VW/Audi issue. If an issue as significant as the VW problem was common to DI engines, certainly the LNF's have have been in service long enough in a variety of applications to have had this happen.  Absent any driveability complaints, there are only two ways to find out;
1) Remove the intake and take a look, or
2) pull the butterfly and inspect the backs of the intake valves with a flexible fiber optic bore scope.

[Sol Asylum]

Ah, but it's not in a gas state... it's atomized in the air...

Think of a humid day. The water in the air isn't in a gas state... that would require it to be over 212F to make steam. The water is just in sufficiently small droplets to be suspended in the air.

Same thing with gasoline in intake air (non-DI).

Like I said this is a different topic all together.

By definition vapor is a gaseous state of a liquid under normal conditions.  Water in the air is actually water vapor.  When you boil water you are breaking hydrogen bonds between the water molecules.  The water molecules will stay separated until a given body of air becomes saturated with water molecules and then the molecules will condense back to a liquid form.  There are several variables which control when this saturation will occur.  A droplet would imply that it is in liquid form which is not how the water in the air (humidity) is suspended, its a vapor.  When humid air becomes saturated you end up with precipitation which also includes fog.  Think of it this way when water in a liquid state is in the air it decreases visibility because the droplets will refract the light.  Water doesn't have to be at 212 to break hydrogen bonds either if it did we would never have water evaporate and as such we would never end up with rain or other precipitation.

The idea that water boils at 212 and freezes at 32 is not cast in stone water can be in a liquid state below 32 its actually how hail and freezing rain occur.  Given the right conditions, a vacuum, you can actually make water boil at room temperature, this is how they remove water from air conditioning systems before servicing them with freon.

See mom I did pay attention in chemistry class, she would be so proud.

SOB is correct in that so far I haven't heard of any Kappas with this issue only VW/Audi which to me means this is not a DI engine problem but a German design issue most likely with oil control.

[MGar]

I can understand the Audi's in this being the worst effected, because they are N/A.  An NA engine will depend far more on clean valves than a FI engine, that's not to say that an FI engine will be unaffected.
I've heard also of this being a problem with MS3's, which are DI 2.3T, but also, they are notorious for having less than adequate PCV systems, and an oil separator is a good idea for them.
I've had my TB pipe disconnected several times, and never noticed oil in it, nor was there oil in the stock intercooler when it was pulled out.  That said, I'll probably run some seafoam in the vacuum system just to be safe around time of the next oil change.