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Thread: Preventing and Fixing Carbon Issues for Direct Injection Engines - Humble Mechanic

  1. #1

    Preventing and Fixing Carbon Issues for Direct Injection Engines - Humble Mechanic


    I think you’ll find this video interesting because it sounds like dismantling and cleaning of GDI engines is a general issue for VW.

    Think this is more of an issue for GDI engines in general? I have not heard of other engines needing to be disassembled for cleaning because of carbon deposits.

    However, I also found this which partly answered my question:

    Is Carbon Buildup a Problem With Direct-Injection Engines?

    "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."
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    Laszlo - red '17 WRX
    The all-new Subaru WRX is coming. Pardon our dust.

  2. #2
    That's part of the reason my car is split port/direct injection, port injection sprays fuel over the intake valves and cleans them automatically.

    VW definitely isn't the only company that has had issues with carbon build up, but they have been using direct injection for a lot longer than most companies. There's a few articles online showing the FA20DIT (2015+ WRX and Forester XT engine) is showing significant build up pretty early in life.
    Last edited by wparsons; 07-25-2016 at 03:43 PM.
    2013 FRS - Daily enjoyed.

  3. #3
    I remember reading somewhere that in VW's patents for their GDI engines, they did note carbon build-up is an issue. Needless to say, a lot of RS4 owners were pretty pissed to be losing anywhere up to 30-40hp at the top end after only 20k miles.

    VW engines certainly aren't the only ones with this problem though. How manufacturers will address it seems to vary a little bit. The current generation LS engine (LT1) is now direct injected. GM claims their PCV system has been redesigned to mitigate carbon build-up. As Will pointed out, Toyota (e.g. the FR-S / BRZ) use dual injection to solve it. VW is also now using dual injection (e.g. in the current EA888).

    All fine and dandy for future iterations, but for folks like us we're stuck with the problem. From what I've been able to gather, air-oil separators don't help. Water/meth injection seems to prevent additional build-up but won't really clean away anything that's already there. The only thing you can do is pop the intake manifold off once in a while and clean away.
    Mike E

  4. #4
    Same at Hyundai and likely every manufacturer as well.
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    The three most feared words in racing: All Wheel Drive

  5. #5
    and more...

    MAY 20, 2013
    This bulletin provides information regarding fuel system recommendations for Hyundai
    vehicles equipped with Gasoline Direct Injection (GDI) engines. GDI engines operate at
    much higher fuel pressures than regular gasoline engines and as a result specific fuel and
    maintenance items are recommended to ensure optimum operation of these vehicles.
    Vehicles that do not follow these recommendations can experience drivability issues such as
    rough idle, lack of power and pre-ignition that may or may not trigger Diagnostic Trouble
    Codes (DTC) stored in the ECM/PCM. Hyundai recommends that dealerships advise vehicle
    owners of the following recommendations whenever a customer vehicle is in for service.
    The use of high quality gasoline contributes significantly to the proper running of a GDI
    engine. Poor quality gasoline can contain sediments, suspended water and low quantities of
    detergents or fuel system cleaners. Use of poor quality gasoline can lead to engine deposit
    build up and vehicle drivability issues, in both GDI and non-GDI engines.
    To prevent these issues it is recommended that vehicle owners use gasoline from high
    quality fuel suppliers. HACC recommends the use of gasoline that is recognized as “Top
    Tier” Detergent Gasoline. Information on recognized Canadian and USA retailers of Top Tier
    Detergent Gasoline can be found at
    The use of a fuel system/injector cleaner tank additive is part of the vehicle recommended
    maintenance schedule for vehicles equipped with GDI engines. This fuel system cleaner is
    recommended to be used every 6,000km to maintain optimum engine performance and
    should be added every oil change as part vehicle preventative maintenance. The use of a
    fuel system additive can help prevent build up in the engine and fuel system and prevent
    vehicle driveability issues. Use of a fuel system cleaner is a customer pay maintenance item.
    Dealers may order the fuel system cleaner through the regular parts ordering system using
    part number: 084NA-26004.
    NOTE: Normal warranty policies and procedures apply.
    Hi, my nickname is \"Smiley\".

    Looking for a New Hyundai or used car? Ask me!

    The three most feared words in racing: All Wheel Drive

  6. #6
    I found this AAA study on Top Tier fuels:

    Key Findings from the Abstract re-listed here:

    Key Findings:

    1. The test engine operated on a TOP TIER gasoline averaged 19 times fewer intake valve
    deposits than when it was operated on non- TOP TIER gasoline.

    2. Based upon secondary research findings, long-term use of a gasoline without an enhanced
    additive package can lead to reductions in fuel economy of 2-4%, drivability issues, and
    increased emissions.

    3. In most cases, carbon deposits can be reduced or removed from critical engine components
    by switching to a gasoline that meets TOP TIER standards.

    4. Approximately six in ten drivers (63%) believe there is a difference in the quality of gasoline
    sold by retailers, yet only (12%) of drivers purchase gasoline based upon its detergent
    additive package. The primary motivation for choosing a particular gas station is location /
    convenience (75%), followed closely by the price of the fuel (73%).

    5. Most TOP TIER gasolines do not cost significantly more than non-TOP TIER gasoline. The
    average price difference between the TOP TIER and non-TOP TIER brands surveyed was
    three cents per gallon over a 12-month period.

    So I'm not the only one interested in the cleaning properties of gasoline fuels. :P
    Last edited by LaszloT; 08-03-2016 at 08:26 AM.
    Laszlo - red '17 WRX
    The all-new Subaru WRX is coming. Pardon our dust.

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