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GDI & Carbon Build-Up on the Intake Valves

JayTheCPA

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Am presuming that the deeper experts here are already familiar with the carbon issue in GDI motors.

Seeing as diesels are not experiencing the issue and are pretty much the same from the air intake perspective, any thoughts on / experience with why gassers are seeing carbon build-up where the diesels do not?

Only real difference in the system that I can think of between the GDI and diesel is properties of the oil, but also saw where others had already discounted this.

And, just how real of an issue is this? The only manufacturer that apparently has the carbon build-up bad enough to effect the motor is VW with their 2.0L & 3.0L motors. While all the other manufacturers are experiencing it, the reported failures from carbon are statistically insignificant where it is easily possible to go 150K+ miles without needing to take any action.
 

Will L.

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Almost all gas is injected near the exhaust valve(s) opposite the intake so the incoming air causes more mixing of the liquid fuel into a mist, then mixed as vapor.
The tininest anything on the gas injectors or exhaust valves in the way causes a sprayed mist to splash instead of getting mixed into the high speed air coming in.
This of course means a microdrop of unburned fuel. Which at a few thousand rpm is a crap ton percentage wise.

So don’t think the amount of carbon gdi panic happens at is anything like what we saw 1960 or 1970s engines look like when pulled apart. If the valve or head area collects the mass equalling a dime- it will have issues.

Some engines designers that take emmisions seriously will cause 4-5 very rich cycles or two followed by couple lean burns with spark advanced timing . The added fuel softens the carbon and then being “wet” and the super hot couple cycles flashes of the carbon chunks and sends the flakes out the valve. When that isn’t written in as an electronic wrench, then Terry Too Tall is happy to schedule your dealership appointment...

Going into your way back machine to ww2 is a better option. Yes carburetors and points! But besides bringing that back to the future, steal off an airplane- WMI!
When all the high dollar chemicals have a fit with it and dont get it, good old distilled water at high rpm and just add more till the engine bogs, while puking enough black smoke to make Ed Begley cry. The water just dislodged the carbon and sent it out for some ozone cleaning. Oops, should have had an airfilter on the tail pipe!

So it’s really all an emmisions problem trying to burn amazing percentages of the fuel and when tolerances are too tight for the gas itself- it goofs up.
As for VW: you really gonna ask anything about emmisions and VW? Haha- ok, that I will leave to out German friend, if he isn’t on a motorcycle riding at the moment...
 

THEFERMANATOR

FRANKENBURBAN
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It IS an issue, and most I've seen say you better do a decarbon on them every 50K miles. DFI gas engines all suffer this problem, some worse than others. It's no different than the carbon buildup you get in the throttle body of any gas engine that injects fuel after the throttle body. The vacuum created in the intake tract pullsthe carbon out, thats why you don't see it in diesels because there is no vacuum in the intake.
 

Will L.

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I saw where Ferman said “IS” in caps and was afraid I made
It sound like I meant do nothing- which is not my belief if it came out that way. Don’t think I did, but jic, yeah clean it!

I did notice I didn’t mention, a huge part of the problem of GDI is since no fuel goes across the intake valves, they get dirty the worst in the cylinder. Gasoline is a great cleaning agent, as many of us learned using it to clean everything for much cheaper than degreaser in a can. And with no fuel cleaning the intake valves since it never touches them...

On the tool truck I used to sell a real nice canister unit that you could pour a concentrated liquid cleaner into, then it sucked the liquid down a vacuum hose while you ran the engine at higher rpm- 2k, maybe 2500rpm. Then shut it off for a while to let it soak in, then drive the truck to blownit all out. Now days you can buy a spray can with a little weaker chemical to do the same, it just takes more liquid, sometimes a second treatment.

The beauty of distilled water is, it’s crazy cheaper and does it faster. But it can throw codes because all the water plays with the oxygen ratio in the exhaust and can cool heated o2 sensors. So many of the shops I went to as a tool Guy that knew the water trick, just laughed at the $100 decarbon can.

For years i have done the water trick before I tear down an engine. I had guys that didn’t believe what I told them, so I made a bet when i could do individual cyliders or banks. $100 if I loose and if they loose, they clean the carbon on the nonwater side and they owe me lunch.
Lots of double double combos I ate while watching them scrape in my bay. Haha. I was mean to one guy and hooked him for $200, but he was a total jerk to everyone.
I don’t suggest doing it to an engine you are about to open up and you are trying to diagnose a problem or examine running performance- don’t want to remove evidence.

@THEFERMANATOR good thinking about it pulling some carbon out if the fuel under a vacuum. I never thought of it, but always just figured that was varnishig and fine dirt- but that carbon make perfect sense. The gas would wet the carbon but without the heat and explosions to shock it off, no way to be removed.
 

JayTheCPA

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Interesting point about the effects of vacuum. Thanks Ferm!

The GDI rig I am running now does stay in vacuum when not under load. Perhaps this is why that motor is known for going 150K+ miles without the carbon build-up causing any real issues other than its mere presence. I was tempted to work with a tuner to see if there was a way to run the intake pressure closer to neutral when under light load, but now I am thinking it is better to leave the boost profile alone.


Will, already knew about water in the WWII aircraft. WMI seems tempting as I can see how it might avoid carbon build-up by acting as a repellent (presuming it condenses on the valves). Am not so clear on how water might remove carbon build-up on the valve stem in a GDI once the oil vapor settles and cokes. I had an old Merc IDI with series GP's, used starter flud on the GP's to clean off the carbon (removed the GP and direct sprayed it), and that stuff worked great. Not so sure I want to spray starter fluid on a running GDI motor though . . .


One thing I had seen kicked-around was to install stiffer valve springs. Reasoning was that stiffer springs would more likely crunch a piece of carbon rather than have that piece lodge and hold the valve open.
 

JayTheCPA

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Ferm, just re-read your post and originally read the vacuum effects backward . . .

So, by working with a tuner to re-map the intake pressure to minimize the vacuum, this might help prevent the carbon build-up?

Aside, I was surprised to see a charged system want to run with vacuum as (to me) this indicates the motor has to do more work for ingesting the air. Put another way: vacuum = lower efficiency. By at least keeping the charge at zero psi, the motor can spin more easily.
 

THEFERMANATOR

FRANKENBURBAN
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I understand the need for DFI due to emissions, but it is beyond me why they don't put 1 small fuel injector mounted above the throttle body, or right after it, and do away with all this carboning problem. Some are running both DFI and typical multi port injection to deal with the carbon build up issue. A single fuel injector designed to super finely mist the fuel injected before the throttle body would stop the carbon build up and I doubt would negatively effect emissions much at all if any.
 

Will L.

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The wmi wont clean the valve stem. The face of the valve where it seats, yes because the water will basically soak the carbon weakening its bond with the methonal helping break it down. When the heat and shock of the explosion hits it can break free.
Now if the valve wont close because there is a piece of carbon there, the steam expansion during the explosion will remove that piece of cabon exposed to the explosion just like it does inside the cylinder.

Think about when the decarboning treatment is done. There is a mist of the chemical that gets into the airstream at the intake plenum after the sensors. Some of those chemicals are water based and some are petroleum based, it depends on brand. The liquid does the same thing the WMI does. It soaks the carbon, it has a cleaning agent in it (WMI Using methonal as an amazing cleaning agent) and problem solved. The decarboning procedure can be done with a 50/50 mix of distilled water and methonal- wanna guess EXACTLY what made up the brand that was sold on the tool trucks for years?
I know several tool truck guys that made their own, just a trip to the pump station that sold methonal, mix at home w/ water and sell to the shops they went to.

And the mechanics in shops dont usually do “entire bottles” btw. They get it in bulk and use the reusable canisters. The canister holds enough to do 4-6 engines depending on which brand tool and what size engine. A 3.4 liter needs a bit more than a 1.8... So the mechanics just hook it up, and run for “X” amount of time. I would say only 10% of mechanics read the spec that a certain engine should use exact amount and actually measure it out. These are guys in dealerships too, not just Joey’s garage.

When you diy, the spray cans say use entire can for one service. But a 4 cylinder 2.5 vs a 6 cylinder 3.2? And what about 2 valve per cylinder vs 4 valve in the same size engine?

Thefermanator mentioned why don’t they all do 1 small injector to apply a tiny amount fuel for the cleaning would be a good idea. I agree but instead of one more gasoline injector, I am saying WMI instead of gasoline. Either diy treatment or keep it clean all the time and get the benifits of wmi all the time. That is more expensive investment however. But the vacuum wont pull apart the water from the methonal. Going into a vacuum is better infact because a drop in atmospheric pressure causes more expansion into a finer mist. That why the low pressure wmi systems have to use raised pressure depending on boost pressures.

As for changing the valve springs NO. If you are modifying the engine for power, mpg, etc then spring changes to match your modification makes sense, but just like any engine it needs to match your build.
On a 6.5 that only had 10psi boost the factory springs are ok, but you ramp up boost to 20 psi and you need stronger springs. But stronger springs cause more drag and you loose power and efficiency at the lower rpm when boost is 10 or less because it takes more energy to open them. Also it can wear the components more, but lucky for 6.5 all that stuff is really well built for strength.
Can the stock camshaft in your engine withstand it? Rest of valvetrain? Can of worms what needs to be changed. What performance issues are you creating to smash some carbon on the valve face- that got there EXACTLY HOW AGAIN? Even so Then here is a thought. Trying to use the valve and seat as a hammer and anvil isn’t great. I would rather the backfire for a few cycles until it clears, Providing it is a not an interference engine. I would imagine they aren’t because otherwise you would hear of them all being destroyed from it.

Likewise- a tune to lessen vacuum? NO
Um, I don’t understand tuning 1 bit To drop vacuum. The vacuum is produced by good ring seal and the piston going down on the intake stroke, and the relationship of piston cc to intake ports, to intake plenum. Optimizing lower vacuum and airflow is called porting the heads, intake, etc. the vacuum lowers but the flow increases. The computer could cotrol valve timing to affect vacuum, but I don’t see how that would help anything- hurt infact.

The vacuum possibly pulling the carbon out of the fuel shouldn’t affect you anyways. Your vacuum is from the airfiler to the intake valve. Then valve closes, cylinder gets compression and THEN your fuel gets injected into the cylinder ONLY. If it were exhaust valve build
Up then ok, your fuel Can be causing it. Your fuel never sees a vacuum scenario. How does the gas get onto the intake valve back and stem to build up? It can’t.

So where is your carbon coming from becomes the question. Valveguides/ seals is the logical point imo. Intake valves always leak oil before the exhaust of natural aspiration engines because the back of the intake valve against the seal is under vacuum sucking oil towards it.
On boosted application the exhaust valve leaks same rough time because boost pressure goes against the intake valve, and exhaust back pressure for the exhaust valve building boost.

Carbon deposits on the cylinder side of the intake valve makes sense because it is where loose cabon is generating as the fuel gets burned.

But honestly when it is just in cylinder carbon, no matter gas or diesel, di, idi, carbureted, etc- I just open access to the plenum, go to 2,000rpm, and give ‘er a drink of water until she quits puking smoke.

One other thing I learned going to all those dealerships- All that carbon has to go somewhere. How soon donyou want that new catalytic converter installed? So if it has a cat, i remove the connection to the cat for,,, um,,, safety inspection- YEAH THATS IT, safety! Then when she is done puking, I usually realize that was the problem and hook back in the cat and clear the codes.
 
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