Is Carbon Buildup a Problem With Direct-Injection Engines?

Is Carbon Buildup a Problem With Direct-Injection Engines?

Direct injection offers numerous benefits over port fuel delivery but could it be a bigger headache than it’s worth?

The automotive industry has gradually switched to direct injection over the past decade or so and for good reason. Spraying a precisely controlled amount of fuel right into an engine’s combustion chambers can result in improved efficiency and greater power density; tailpipe emissions are generally cleaner as well.

In spite of these advantages, this technology isn’t perfect. DI has a handful of downsides including additional noise, particularly at idle and dramatically higher costs, though there are other concerns.

And a big one has to do with carbon deposits. We’ve heard rumblings that blackened buildup on the backsides of intake valves is a major problem and something that could be disastrous for motorists in the coming years. To get to the bottom of this potential top-end issue we did some digging.

What’s Really Going On?

CarbonFord has been pushing its EcoBoost engines as a way of improving fuel economy without sacrificing performance. The real-world results of this strategy may be mixed, but one thing is not: all of these powerplants feature direct injection as well as turbochargers and advanced control software.

These engines have been on the market for a number of years now and to get some empirical evidence from the front lines about how they’re holding up we reached out to Brian Laskowski, a Ford Factory Certified Technician. He also has a YouTube channel, FordTechMakuloco that highlights all sorts of automotive repairs.

Responding via e-mail Laskowski said, “Carbon deposits in Ford engines are not a widespread issue due to the advanced engine technology.” But he also mentioned that it has happened in some low-mileage EcoBoost units.

SEE ALSO: What is Top-Tier Gasoline?

“As of today the issue seems to be isolated to certain markets with varying factors such as fuel quality,” said Laskowski. If carbon buildup becomes severe he said it can result in all kinds of issues from drivability woes to misfires, turbocharger issues and even catalytic converter damage.

Survey Says…

Assuaging potential sky-is-falling fears, Michael Karesh, the developer of said carbon buildup is “not an issue for all direct-injected engines” based on the data he collects. His website surveys the owners of around 33,000 different vehicles to acquire relevant and timely data about vehicle reliability and fuel economy among other things.

But of course there are some instances of deposit-related issues that have popped up. Karesh said, “The only engines it’s reported quite a bit is [with] the VW/Audi 2.0T and then the Audi V6s.” He also said, “I know there are some BMWs that end up with carbon buildup as well.”

As for the frequency of reported problems with these Volkswagen cars he said his numbers indicate “it can be as high as one in six over the last two years,” which “is a high number” and one that he said is consistent across different models.

Carbon Buildup

The 2008 Audi A3, which offered a 2.0-liter turbocharged four-cylinder engine, also popped up in the TrueDelta data. Karesh said it’s puzzling why 2006 and 2007 models aren’t having similar carbon issues. Leaving us with more questions he said, “I’m not really seeing GTIs [popup],” which are mechanically similar to the A3.

“If there is a non-German car there might be something happening in the [Cadillac] CTS,” said Karesh, but once again he cautioned that it’s “too scattered and sporadic” to draw any definitive conclusions. Additionally he said, “I have one report of decarbonizing the engine in a Chevrolet Equinox.” Unlike the other instances, he has quite a large sample size for this particular vehicle, which clearly indicates that deposits are not a major problem at this time.

The Whys and the Hows

But how does this buildup occur?

“One of the biggest problems with direct injection is that the fuel is no longer being sprayed onto the backside of the intake valves,” Laskowski said.

This mist of gasoline actually helps keep the intake ports clean. In addition to fuel quality, he said things like valve and injection timing are key factors in carbon buildup.

Additionally software plays a huge role. “What I think is most overlooked is the PCM calibration itself,” the engine-control computer.

“I believe it’s the absolute key to preventing the bulk of this buildup by making the air and fuel burn as completely and cleanly as possible.” Laskowski also said a simple software update can yield dramatic results.

But if something does go awry with your EcoBoost engine and there are drivability issues associated with deposits, Laskowski said the only Ford-approved course of action at this time is to replace the cylinder head, though he also said, “Manual cleaning with a brush and various carbon dissolving products has been used with great success on vehicles out of warranty.”

Beyond outright replacement or lots of elbow-grease there are other ways of of dealing with carbon buildup. Laskowski said there’s a media-blasting technique that can clean engine intact tracts but the method is currently not approved by Ford. Regrettably he said, “In any case the service to remove the carbon can be time consuming and expensive.”

Down the Road

As for the long-term reliability of engines with direct injection, only time will tell if carbon buildup is a serious issue. But for the most part it seems like an isolated problem, at least at this time.

When asked if he’d hesitate to purchase a vehicle with DI because of this issue Karesh said no. “I’m not seeing it for anything after 2010 or so.”

SEE ALSO: What is Octane?

“I think even though direct-injection technology is far superior today compared to a decade ago that with varying fuel qualities, different driving techniques and overall aging of the engines it will be an issue for some,” Laskowski said. Going on he said Ford should develop a cleaning process for EcoBoost powerplants so carbon can be addressed without completely tearing engines down.

DecarbonizingConventional induction-cleaning services aren’t recommended with Ford’s EcoBoost engines. Laskowski said turbochargers can be damaged and they ain’t cheap to replace. “Again I believe the bulk of this problem can and will be eliminated with future PCM software-calibration updates.”

For the time being Karesh said that according to his data, “Clearly it’s a VW/Audi problem and not much else.” Elaborating he also said, “We’ve got other direct-injected engines and it’s not showing up for those.”

Since carbon-related issues with direct injection seem to be sporadic at best Karesh said this is good news for drivers. “It means you don’t have to plan on decarboninzing your engine every two years for $800 a pop.” When asked if deposits could become a nightmarish issue in the future he said, “I can’t say. I don’t have my crystal ball; it’s in the shop,” and hopefully not because of something related to carbon.

GALLERY: Ford 2.7-Liter EcoBoost Engine


Discuss this story on our Ford forum

  • Jonny_Vancouver

    I think this is a more wide spread problem than we’re currently aware of. In the case of Mr.Laskowski & Mr.Karesh, their data is very limited and not at all indicative of the majority of direct injected engines on the road today, but some info is better than no info so thanks autoguide for reaching out to these professionals. I think it’s clear that the technology is still being perfected, I didn’t know DI engines are noisier in general … It is truly good news if the carbon buildup issue can be solved with software tweaks, other than that, a simple carbon cleaning technique would be welcome and should be covered by each car makers warranties or built directly into a DI engine, like a self cleaning oven.

  • craigcole

    Thanks for the comment. Carbon build up, if truly an issue, has the potential of becoming one huge problem in the coming years since SO MANY engines have this fuel-delivery technology. With proper maintenance and good fuel it sounds like it can be side-stepped to some extent but we shall see.

  • Jason Wang

    It’s great to see publication such as AutoGuide bring up such an issue.
    In regards to ecoboost. Ford and Mazda apparently co-developed their 4cyl engine back in the days. The 2.3L DISI engines used in the MazdaSpeed products seem very similar to the Ford Ecoboost 2.3L. The DISI engines had a well known carbon buildup issue. The EcoBoost engines are used in the new Mustang and the upcoming Focus RS.
    For VW/Audi engines. VW supposedly have multiport injection used in some of their engines. It employs both port and direct injection. The euro spec new Golf R supposedly has it, however the North American version is still not finalized yet. Could AutoGuide or somebody provide insight on how effective their layout is for preventing carbon buildup?

    The Focus ST and RS seem to be doing direct battle with GTI and Golf R with striking similarities in packaging. It’d be a shame if these great cars are ruined by carbon buildup.

  • Michael

    if the manufacturer has not yet provided the statement to prove that this issue has been solved then it is in my best interest to take action on my own car. without the spray of gasoline on the back side of your valves it will inevitably accumulate carbon brought in from your blow by gases. The only way to prevent failure from high mileage down the road is to install an oil vapor catch can. it is something to strongly consider with DI engines. just some cents.

  • Mike

    Great article. I own a VW Golf GTI 2013, and I had a major engine failure at 21,000 km due to carbon buildup. Luckily my car was still under warranty, and the local VW dealer replaced the entire cylinder head due to the large amount of carbon deposits on the valves and cylinders. I had to keep my car for 4 weeks, but was provided with a relief car during this time. When I asked the dealer how often does this issue happen, they noted that it usually happens at 130,000 km or above for most VW cars!!! What really surprised me the most is that they are aware of this issue and it felt like they were hoping that the failure will occur post the warranty so that we end up paying the entire cost!! Ironically, VW posted an article in 2001 stating all issues of the direct fuel injection system and how it can lead to carbon buildup, and they still used it in recent models!!

  • shrike1978

    My 2008 Jetta 2.0 TFSI had a valve failure at 36k miles due to carbon build up. I left work that day, got onto the street, pressed the accelerator and lost a cylinder as soon as I did. I had used nothing but Top Tier fuel the entire time I owned it, mainly Chevron and Shell, so I question how much good fuel can actually help. This seems to be an endemic issue that cannot be truly solved through any engineering means. Having nothing on the back of the intake valves to clean them is a recipe for disaster.

  • Randall

    A catch can will eliminate this problem but it needs to be installed as soon as possible because if you install it too late it will only keep it from getting worse but if you are already at 75,000 miles or so you will probably have to do a cleaning service to remedy the problem. I have a 2012 VW GLI with the 2.0 and it has been great but I did the right thing from the beginning

  • Randall

    Use a catch can to eliminate the PCV gases/blowby from going into the intake and you will never have to worry about this again!

  • Zachary Zarko

    There are a bunch of Youtube videos where mechanics insert boresight cameras into the cylinders of Ecoboost engines. Most of them do show some carbon buildup after only a few thousand miles.

    I think it’s stupid how Ford designed the turbos. They are not easily accessible at all. If one could easily remove the turbos, it would be simple to clean out the carbon deposits by running some cleaning chemicals through the engine. (But if you do that without removing the turbos, you will literally fry them and have to replace them – and they’re extremely expensive.)

  • nnn

    GM ecotech engine has same carbon build up issues but the more bold problem is a timing chain slack becouse of fuel slowly seeping into crankcase from high pressure fuel pump, just like in good old days carburated engines. Fuel accumulates in the crankcase and destroys upper galvanized layer on chains tracks. As a result, timing chains had become a maintenance items, specially in colder climates, which relatively easy on 4cyl Equinox but painful on 3.6 Acadia etc.

  • Omar

    I have a similar problem with my VC CC 2013. The engine lamp came on after I hit 42000km. Because it was under warranty, they replaced the cylinder head and all of its sister components. But the lamp came back on again. Took it back to the dealership, they said it was a programming fault and fixed it. Came back on again on my way home from the dealership. Can’t really make out where this is headed, my warranty expires in two months too.

  • CogitoErgoZoom

    It why Mitsubishi was the first to have it with its GDI and the first to remove it, too many issues and carbon build up

  • Honesty Counts

    Here is why carbon is forming: Oil vapors are coming into the intake tract from the crankcase via the PCV valve. They flow nicely until they reach the HOT SURFACES around the intake valves, at which point the oil in that vapor tends to ‘STICK’ to the metal surfaces and ‘COOK’ into a form of carbon. That’s it, that is what’s causing all of this carbon. The turbo boost in turbocharged engines increases the pressure in the engine which actually causes MORE vapors to be pushed into the PCV system, making carbon deposits worse.
    Now you can simply pull off the PCV hose from the PCV valve, and leave the PCV valve open, but you will have to put a plug on the PCV valve hose itself to avoid a massive vacuum leak that would cause the car’s engine management system to trigger a ‘check engine’ light. As long as you plug up the PCV valve hose everything will be fine, but with the PCV valve open you might now get oil vapors coming out from it, making a bit of a gooey mess of your engine bay. But your intake valves will remain clean.

  • Honesty Counts

    Or, just pull the hose off of the PCV valve, and put a plug in the now disconnected PCV hose. That way the oil vapor coming from the PCV valve will go all over the engine bay, messing up the outside of the engine, but won’t foul up the insides your engine itself.

  • Honesty Counts

    There are a lot of people who are having the ecoboost engines in their Mustangs self-destructing. Probably due to excessive oil vapors being injected into the intakes, either leading to premature detonation because the oil vapors are lowing the effective gasoline octane levels, or by forming carbon deposits. I think it has more to do with the octane levels dropping and then BOOM, you get premature detonation and damage to the engine itself. All caused by oil vapors from the PCV valves.

  • Paul

    2012 GTI had big carbon issues. It was all stock and driven reasonably by an adult. At 60k VW told me I needed it cleaned and they would be glad to do it for $800. I walked out and tried it myself with injector cleaner. I got “lucky” and had my intake manifold fail (under warranry) and while they were in there they cleaned it for $200. I wasnt thrilled, but i got it cleaned, and sold it. I’m done with VW, and i’d like to be done with DI as well. I have 100’s of thousands of miles on Hondas and Toyotas and never had anything so ridiculous become a problem.

  • Paul

    The manufacturer should just fix it. Its a known problem. I didn’t buy a new car, seeking reliability, to have to rig stuff to work correctly. While a catch can might work, there are people in forums that beg to differ. This shouldn’t be happening to new cars.

  • Dan

    I have $ 1,200 into my VW Tiguan now with 98,000 miles. Never again will I buy DI. If I do it’s my first tool for negotiating the vehicle price down.

  • Hucky Cardino

    I don’t see how the quality of gasoline will have anything to do with the build up of carbon. These engines are direct injected and the fuel never sees the intake side off the valves. The build up is clearly the absence of gas washing the intake valves. The oil could come from the crank case vent or the valve stem seals. I’m currently having my 2011 5.2L -V10 Audi valves cleaned and I’m having to pay for this out of my pocket because the extended warranty won’t cover it. The charge is way more than any $800.00 for a 2.0L but the work is a lot more labor intensive. Has anyone been able to get this covered under warranty and what argument did you use?

  • JuLee Reeves

    Just learned I need to have carbon buildup cleaned and it’s not gonna be cheap. Italian tune up would have been more fun if that would have prevented it? Oh well – looking forward to having her zooming around again – once the CEL came on, the power loss was BAD. 80K miles so guess it was going to happen at this point.

  • Honesty Counts

    For a catch can to work, the oil vapors would have to cool off and the oil would then condense out of the air and into the catch can. But the vapors don’t stick around long enough to cool off, they go in the can, and a few seconds later into the engine. You would have to have a separate radiator just for the PCV vapors so that the oil would condense out of the vapors. That would work, but where would you put the small radiator ( a small radiator, 12″ x 18″ would do okay ) in today’s crowded engine bays?

  • David Sumner

    My wife has a 2010 Audi TT and it’s in the shop with this issue for the second time. First time it had just under 50k miles so it was a warranty issue. The car now has 98k on it and has the same issue and is going to cost $1200 to clean it. It has only had The top Shell or Mobil fuel so I can say that didn’t help.

    It’s a pity because we both love the car. However, we are going to get rid of it and move on to another manufacturer. For the kind of money these vehicles cost, we shouldn’t have to spend $1200 every 50k miles to keep it running.

  • crspcritter

    I put a catch can on our di v6 camaro. Suppose to cure- I get about 1 oz – 2 . of oil when I drain catch can at 5k oil change. But now I read an article in a magazine says carbon issues in di are not from pcv but from the egr-. They say its not a wet oil build up – its a dry carbon that sticks to the cold valve stems from the exhaust gas recirculation system. They recommend synthetic oil and a top tier gas only the octane number you need.

  • crspcritter

    Its an egr problem- dry carbon sticking to cold valve stems –

  • crspcritter

    This article was by Paul koemer world class gm service tech and bosch – Topic : carbon concerns- direct injection aids performance and economy – but does direct injection have a downside ?

  • crspcritter

    They recommend fogging the engine occasionally with gm cleaner 88861802 ,

  • Tony Battaglio

    my vw jetta is in shop now for this , already had the failed intake and failed fuel injector.

  • starskeptic

    Unfortunately, injector cleaners don’t address this issue.

  • Mike

    This in my opinion should be the responsibility of the manufacturer. If they have the solution they should provide it to all VW owners free of charge.

  • Kenneth

    The carbon buildup is from both the PCV and EGR: Oil mist from the PCV coats the valves, while hot exhaust gases bake the mist onto the valves. “Top Tier” or otherwise – gasoline never touches and cleans the intake valves with direct injection systems, and THAT is the problem.

  • crspcritter

    Top tier = less carbon –

  • vdubluv

    Had this done to a few of my VW CC’s, cant get it covered by warranty, however my intake manifold needed replacing, since this became a recurring problem with various models VW extended the warranty on the intake manifold to 10 yrs or 120k (I believe) so this was covered, my car had around 65k miles on it when I had it replaced so I asked how much they would charge extra to do the carbon cleaning while it was removed- paid an hour of labor ($120) and the rest warrantied. With my previous VWs I was lucky to have had a brother who worked as a VW mechanic for some time so he did the service for me for a case of beer and pizza!

  • Okc Dave

    Nonsense. The F A C T is that people who have installed decent catch cans, have emptied a lot of water and oil residue out of them, a very clear sign that a significant amount isn’t making it back to the engine.

    Do you always pretend to know things that you have no experience with?

    Further if you delete the whole PCV, not only will it make a mess in your engine bay, it will also operate without vac so more contamination remains in the oil, fouling it faster and contributing to accelerated engine wear.

  • Okc Dave

    Nope. There is no “proper maintenance” that matters, unless proper maintenance is going to include paying at least several hundred dollars out of pocket multiple times during the viable lifespan of the vehicle.

    Fuel also does not matter, quite the opposite that a good fuel detergent package would help with port injection because the fuel is introduced before the problem buildup instead of after it.

  • Angus Young

    got a 1995 civic. 240k miles. No DI or anything fancy. no carbon problems. 37 MPG highway. 30 city. Runs as smooth as the day it was new.