By on July 25, 2012

 


 

Kurt asks:

I’ve heard from maintenance shops and oil additive producers that DI engines, especially Audi and BMW, have severe problems with carbon buildup in their valve systems. Might be good to chat about this and also poll readers to see if other vehicles have the same issue. Thank you.

Sajeev answers:

Luckily a previous editorial in our “Ask an Engineer” series discussed this problem,  and it agrees with your assessment.  It also agrees with what I heard before GDI (Gasoline Direct Injection) motors were released in significant numbers here in the USA: my mechanic friend in the UK was the first to tell me about the walnut shell blasting method, discussed here. Using all his subtle British charm in describing his true feelings, you can say that he rather hates GDI engines.  And he’s probably not the only wrench to feel that way.

Which rather blows.  Because GDI (and Diesel DI) is a fantastic concept that makes perfect sense.  It is the next logical step in the evolution of the internal combustion engine. Hopefully we can find a way around engine coking, aside from the obvious answer: running at wide open throttle a lot of the time…that kinda defeats DI’s advantages over port-EFI, ya know.

I wonder if the latest GDI motors, especially the non-turbo versions in many a mainstream GM/Hyundai/Ford sedan, shall meet the same fate of the coke-happy BMW and Audi products you mentioned.

So my question to the B&B: how will technology overcome our coking problem?

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry.

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51 Comments on “Piston Slap: A Solution to our Coking Problem?...”


  • avatar
    Bowler300

    *Much* smaller engines require more WOT. Most cars are way overpowered these days.

    • 0 avatar
      Wade.Moeller

      Once you teach people not to be afaid of WOT, it’ll get better too. A couple people I’ve spoken with have mentioned that they think a car that has once been that WOT will blow the engine shortly thereafter.

      Get onto an Interstate onramp, hit WOT for a second or two and you’ll be able to merge without causing a pileup behind you.

      • 0 avatar
        Kevin Kluttz

        They don’t listen. They would for some reason rather stop and accelerate from that dead stop. And oblivioulsy cause a two-mile pile-up.

      • 0 avatar
        wumpus

        Last I heard, Honda/Toyota figured this out a long time ago (15+ years?) and simply adjusted the accelerator to go WOT once halfway down.

        Personally, I don’t trust automatics enough for WOT, but really don’t trust automatics anyway.

    • 0 avatar
      duffman13

      This. And what Wade says there too.

      On WOT being good for the motor: The old method referred to as the Italian tune-up. The higher gas velocitis and higher heat levels generated by some good old-fashioned WOT driving cook the carbon build-up off in this method. IDK how well it would work in DI engines, but I’d imagine that it does a decent bit of good.

      On WOT being good for the soul: It’s called an acceleration lane, that’s what it should be used for. I have a much easier time merging on to a highway if I go WOT to redline in second or third gear getting on an onramp. It gets me to the speed of traffic in less than 5 seconds and I don’t have to worry about some a-hole barreling into the rear of my car when I merge due to speed differential.

      And modern cars can handle a lot of WOT. I took my last car to a track weekend and it spent 4×30 minutes x2 days between 5-8600rpms with quite a bit of WOT, with no adverse effects.

      Another thing on GDI: would seafoam through a vac line help here? how often would they say to do this? I heard it can mess with cats and I imagine with turbos too, which is the only thing that worries me about using it.

  • avatar
    dave504

    There is a solution – buy an GM 3.6 or Toyota D4-S. The jury is out on the Ford Ecoboost. These are the only three motors on the market that seem to have the fewest issues.

    In the GM DI video, you can clearly see that the placement of the injector allows fuel to be sprayed over the intake valves.

    http://www.youtube.com/watch?v=qd90yHlmfS4

    Toyota uses a hybrid setup that includes both port and direct injection. Ford’s Ecoboost torture test motor showed no signs of carbon buildup, and browsing the Ecoboost forums brings a lot of speculation but not a lot of concrete evidence or engine pics. Audi/VW, BMW, and Mercedes are the absolute worst offenders, but since the average Joe won’t notice the sludging and reduced power, the manufacturers are not forced to fix it. Shame that in the era where every recall is broadcasted across every forum, there is almost no mention of the carbon buildup outside of enthusiast forums. This is great for the manufacturers, as they get to continue to perpetuate the myth of German engineering.

    http://www.audizine.com/forum/showthread.php/336352-Audi-FSI-Engine-Carbon-Build-up-Megathread

    I have been browsing the VwVortex forums and apparently the carbon problems in the 2.0 engines start to occur in as low as 10,000 miles. If you are in the market for a VW, I suggest you wait until 2014, when the new motors will combine port and direct injection like Toyota’s D4-S currently does.

    http://forums.vwvortex.com/showthread.php?5468544-NEW-EA888-1.8-TSI-2.0-TSI-Engine-Details

    I have done a LOT of research on this, because I am in the market for a new car and don’t want direct injection. Seems like the only port-injected engines left are Ford’s Coyote, GM’s LSx, and Chrysler’s Hemi – great if you want a pony car, not so much for a regular sedan that’s not a Charger or 300.

    Most of the fixes that I’ve seen on various forums don’t work including Seafoam, catch cans, better gasolines, winding the car to redline/WOT, etc. The only real solution is the walnut shell blasting or the BG fuel system cleaner. Nothing like having to pay for a partial engine teardown and carbon clean on your $40,000+ German car. I think Shell should be sued for false advertising for making people believe that their Nitrogen gasolines will clean your engine valves when it never touches them.

    As a final note, this is why I don’t trust Consumer Reports or JD Power, as these are serious issues but will never be reported since no one is taking a boroscope to their 20,000 mile engine that’s still under warranty.

    • 0 avatar
      Sam P

      The 3.5 liter 2GR-FSE V6 as used in the Lexus IS350 uses a hybrid DI/port setup. Look at some Lexus forums, the IS350 has virtually no issues with carbon buildup.

      Also, the current V6 Camry uses a non-DI version of the Lexus V6 – if you really can’t stomach having DI in a car.

    • 0 avatar
      tresmonos

      http://www.youtube.com/watch?v=LNfQqHooQZI

      Video of the ecoboost. It shows open valves (like the GM video) during injection.

      I’m still skeptical.

    • 0 avatar
      Pinzgauer

      I have not seen any evidence of this either on the Juke forums. Mine has 34k and does not appear to have any buildup.

    • 0 avatar
      deliverator

      I’m pretty sure Honda isn’t using DI on any of their engines, yet.

    • 0 avatar
      MBella

      I don’t know where you got your info on Mercedes engines having carbon issues. The GDI engines just came out last year and so far seem pretty good. We’ll see in a couple of years if they will have the same issues as their BMW and VW cousins.

    • 0 avatar
      Wheeljack

      The Chrysler 3.6L Pentastar V-6 makes competitive power and does it without DI.

      • 0 avatar
        highdesertcat

        Yep, that is an impressive little engine, that can!

        I own one in a 2012 Grand Cherokee Overland Summit 4×4, and the 290 horses mated to the five-speed automatic have no problems hauling that two-ton-plus CUV up the mountains of Southern New Mexico and West Texas.

        An eight-speed automatic may be even better…..

    • 0 avatar
      DeadWeight

      I can’t believe I’m considering a VW product after my own past experiences and the very bad ones of almost every person I am related to or know who has owned them, but this is why I’d go with the 2.5 liter Passat even though it’s not the latest and greatest technology wise, assuming I go with the Passat.

      I need a bigger back seat and bigger car. I’ve can’t stand the decontenting and cheapening of the major Japanese volume sedans, and I’ve not found a domestic sedan with front wheel drive I like (I do like the RWD 300, but I don’t want RWD).

      The 2.5 in the Passat sounds more refined than it does in past models. As I’d be getting a stick, gas mileage should be ok. The most objectionable thing about the Passat was the road noise, which was so bad that it could be a deal breaker, especially given the lack of trust in VW products reliability wise I already have.

      But I’ll have to hurry if I do buy one new, because they’re going with the 2.0T in the Passat again, soon, as much rumor has it…

      Then again, I’m not a glutton for punishment from a company that’s already shafted me with an inferior product, so I’m probably wasting my time with the Passat test drive and such.

      • 0 avatar
        sunridge place

        Buick Lacrosse…FWD…longer warranty than VW….4yr/50k B2B. Quiet as a mouse…Buick has shortfalls…but noise in the cabin isn’t one of them

        The backseat is huge because of the influence of China. Little known fact…early adoption to China market on higher dollar vehicles valued bigger back seats because the person buying the vehicle often was being driven and had a driver.

        Don’t believe me? Look it up.

        Not sayin’ I would buy one…just saying that bigger back seats for a period of time was due to China. Current Lacrosse dates back to that time…not sure if its still true.

      • 0 avatar
        DeadWeight

        I actually like the LaCrosse, Sunridge, but I can snag a SE manual Passat for about 23.8k OTD (yes, that includes tax, destination and BS fees). I can score an S manual for about 2k less OTD.

        That’s significantly less than what I can get into a LaCrosse for, and the Passat has a somewhat larger rear seat (you’re correct about interior noise levels; the Buick is a library compared to the Passat).

        It’s probably moot, though, as the more I dwell on the Passat the more confident I become I’d regret the purchase at any price.

      • 0 avatar
        sunridge place

        Yep…VW invading the mid size market at lower cost..good for them…but the buyer makes compromises too.

        In segments where GM has decent new product, they are priced higher than the competition. Its always a compromise.

        I think that Buick would rather sell 4k-5k LaCrosses a month at a transaction price in the high 20′s than lower the price to meet your needs with the content they provide. Everyone makes choices. I’d rather see 5k profitable sales in a segment than lower the price to try and squeeze out 7k sales.

        Do the math.

  • avatar
    retrogrouch

    Walnut shells again? I think it has been about 25 years since BMW was doing this regularly.

  • avatar
    JCraig

    I can’t imagine mainstream auto makers incorporating this technology without working out a major bug like this. Especially Hyundai with their 100k mile engine coverage and the potential for a backlash.

    • 0 avatar
      retrogrouch

      The German automakers just want the car to make it through the certified pre-owned warranty period. They could not possibly care less what happens when the car has 100,050 miles. They all stopped caring about the same time as when Mercedes stopped installing grease fittings in their door hinges.

  • avatar
    cdotson

    The pre-injector idea has merit, but seems to somewhat defeat the point of enabling higher compression ratios by eliminating risk of preignition as there’s no fuel present during the compression stroke.

    A single injector mounted at or behind the throttle body that mists a water/methanol mixture would take care of the carbon buildup AND allow further compression increases with the minor inconvenience of an increase of consumable fluid (although it is cheap and all cars already have a bottle and pump for it on board).

    • 0 avatar
      CJinSD

      The linked to article showing BMW walnut shell blasting shows the buildup after 48,000 miles on a direct injection car that has been fitted with methanol injection. It was better than without methanol injection but still not as good as without direct injection in the first place.

  • avatar
    bball40dtw

    On the 2.0T VW engines, you just need to clean the intake every 40K-60K. I don’t think its a big deal. You can DIY for less than $100 or pay someone less than $300 to do it. I don’t know about this walnut shell stuff, I just used solvents and elbow grease. VW/Audi dealers actually sell a fuel system cleaner for DI engines that is made by BG. Next month, when I do the 40K service on my GTI I’ll see if it actually works. The last VW 2.0T I owned had quite the build up by 40K.

    • 0 avatar
      CJinSD

      Any fuel system cleaner is a placebo in a direct injection engine that doesn’t have redundant port injectors because the fuel is never where the carbon buildup issue occurs.

      • 0 avatar
        bball40dtw

        Yeah, thats what I told the dealership. They put it in the oil changes and gas tank on the 3yr/36K service. The only fuel system cleaner that I have used is the BG product that is used to physically clean the intake. Its a good solvent, but the process is a PITA.

      • 0 avatar
        dave504

        The problem is not as much the intake as it is the valves and intake port.

        http://www.audizine.com/forum/showthread.php/298455-Carbon-Buildup

      • 0 avatar
        DeadWeight

        Thanks for that link.

        Fack it. I give up on VW/Audi.

        It’s just not worth the pain.

    • 0 avatar
      bball40dtw

      Dave, I did the whole damn thing. Valves, intake, intake port, etc. There are a few DIY threads on VWVortex on how to clean the carbon build up off. It isn’t difficult, it just takes time and patience.

    • 0 avatar
      icemilkcoffee

      “On the 2.0T VW engines, you just need to clean the intake every 40K-60K. I don’t think its a big deal.”

      Huh? Say what? Having to clean the intake every 40k-60k is ‘not a big deal’? Sounds like a huge deal breaker to me.

      • 0 avatar
        bball40dtw

        Prepare for the worst hope for the best.

        The carbon issue has been a problem, but doesn’t effect everyone. We’ve had three DI, 2.0T, VW engined vehicles. One had significant carbon build-up, the other was clean at 85K. I will see at 40K what my GTI looks like. I haven’t noticed a drop in fuel economy or performance.

        I agree it is a deal breaker if you have to do it on a vanilla C or D segment car or cuv. I knew going in that GTI ownership was going to be more expensive then Corolla ownership.

  • avatar
    Jellodyne

    You got a lot of carbon scoring here. It looks like you boys have seen a lot of action.

  • avatar
    CJinSD

    Does anyone really think direct injection will save enough fuel to pay for a 6 hour shop bill plus $100 in supplies every 50,000 miles? This isn’t instead of some old maintenance expense, this is in addition to paying for everything else that wears out over time.

    • 0 avatar
      bball40dtw

      I agree with you completely, which doesn’t usually happen. Not many people will do the carbon removal themselves. Some VW dealers charge $1000 for the cleaning (Some only charge $300). Since I can can remove the build up myself, and I didn’t buy my GTI to save money, I don’t care.

      I am interested to see what our 2.0 GDI Focus engine looks like at 40K miles. I haven’t heard of any issues from Focus messege boards, but its probably too early.

  • avatar
    jtk

    Mazdaspeed3 guys apparently are using the walnuts too. But then some other people claim it was a PCV valve issue that has since been solved.

    I own a DI Mazda3 (Skyactiv). I don’t think I’m going to do anything special until it becomes an issue (if it does)… and then I’ll clean the intake valves or pay someone to do it for me.

  • avatar
    DC Bruce

    If there’s no fuel being sprayed into the intake system (which is the case with “pure” DI engines) then running WOT isn’t going to make a difference as far as “cleaning” the engine. Somewhere on this forum someone linked to a VAG patent drawing showing a rotating intake valve as a supposed solution to this problem. I would think that rotating the intake valve simply delays the problem.

    I believe the real problem is the blow-by gases that are captured by the PCV system and dumped into the intake. That has a certain amount of motor oil and other crud, which gets coked onto the intake valve stem and the intake passage over time, if it’s not washed off by gasoline in the intake air stream.

    Diesel engines, even the old-style diesel engines that don’t use common rail fuel injection, should always have this problem, since there’s never any fuel in the intake air stream.

    But they don’t.

    My guess is that the reason they don’t is that diesels run at atmospheric intake manifold pressure, so they don’t have PCV systems that suck crankcase gases into the intake air stream (there’s no vacuum to do the sucking). Thus, the intake air is clean and no deposits form on the valve stems, etc.

    So, the real question is, how can we get rid of PCV systems that throw crud into the intake air stream of all gasoline engines?

    Meanwhile, it looks like the owners of “true” GDI engines can look forward to paying for periodic cleanings of the intake system, including the valves.

    • 0 avatar
      Ubermensch

      I think some owners of DI engines have “illegally” modified the PCV system to vent to the atmosphere. Maybe the crankcase gases could be dumped into the exhaust stream before the cat and have the cat burn it off?

    • 0 avatar
      redmondjp

      You’re incorrect about diesels not having this problem. VW TDI engines (at least back in the 1990s and early 2000s) could have an intake manifold completely clogged with carbon. I removed and cleaned out the intake manifold on my 1996 1Z TDI motor and it was a lot of work – even moreso if you actually attempt to clean out the intake ports in the head (w/o getting large chunks of carbon into the motor which can cause engine damage due to the near-zero clearance between piston and head).

      And you are forgetting the EGR – it’s the hot soot in the EGR that combines with the oily vapors from the crankcase to form the gunk that clogs up the intake ports and valve stems. This is also true on gasoline engines but of course there is less particulate matter in gasoline engine exhaust.

      • 0 avatar
        DC Bruce

        Leave it to VW to screw something up. There are a hell of a lot of Mercedes 240Ds, 300Ds still on the road with several hundreds of thousands of miles without this problem, not to mention diesel auxiliary engines in boats/yachts with 2, 3, 4,000 engine hours which also do not have this problem. It’s been a while since I owned a boat, but, IIRC, the last one I owned, a 36-foot sailboat with a 4-cylinder diesel auxiliary engine had, I believe, a filter in the ventilation system. Usually, these engines need fuel injectors replaced before the head has to come off.

      • 0 avatar
        william442

        Don’t fprget the stack fires caused by big chunks of carbon.

    • 0 avatar
      Wheeljack

      Rotating valves are nothing new. The valves HAVE to rotate on all engines, otherwise the valve head can begin to take on an oval shape and cause poor cylinder sealing/misfires.

  • avatar
    hreardon

    The gen 3 1.8T and 2.0T that launched with the new MQB A3 and the 2013 Q5 both have dual-port injection, partially as a way of combating the carbon buildup.

    Only time will tell whether or not this is a true solution.

  • avatar
    niky

    I wonder how SkyActiv will fare, given that they have cooled EGR instead of “hot” EGR…

    • 0 avatar
      Scoutdude

      Cooled EGR is not new Ford started doing it in the 80′s, or course that was well before DI. The problem being the cooler would corrode and dump coolant into the engine, not sure whether the bulk of the corrosion was from the coolant side due to lack of coolant changes or the exhaust side due. They did introduce a replacement part w/o the water passage. It is also common in modern diesels and some of those are experiencing the same issue.

  • avatar
    stuki

    And here, silly me was thinking it was the BMW’s and Audi’s DRIVERS who were doing most of the coking. To the point that it interferes with their ability to breathe after some years.

  • avatar
    punkybrewstershubby aka Troy D.

    Definitely do a FI service about every 30K. I use a particular two-letter brand in our shop and it works very well on just about every engine we apply it to. It will set you back around $100.

  • avatar
    Andy D

    Coupla old BMW and furren car tricks to de-carbonize valves. First and funnest is the Italian tune up. An hours run at high RPM in a low gear Next is a hot soak used as instructed on the can. Inducing SeaFoam or if you’re really brave , water through a vacuum line

  • avatar
    kurtamaxxguy

    I asked Audi about the known intake coking problem on A$’s and they claimed their switching piston rings (using rings from the A3) solved the problem.
    Perhaps it also lowered the A4′s oil consumption as well? German cars for some reason consume a great deal more engine oil than other brands.

    • 0 avatar
      DeadWeight

      You may have heard me mention it before, but our brand new 2006 VW Passat 2.0T was burning no less than 1 quart of synthetic oil- from the get go- every 1,000 miles.

      When I took it in for service under warranty, the tech I dragged off to the side to speak with admitted it was a problem, but after two days with a loaner, the service manager called me to tell me my car was “ready” and that their testing revealed no problems whatsoever. When I asked if it’s normal for a new car to burn at least a quart of synthetic oil every 850 to 1,000 miles, his canned response was that VW has specified that’s within normal parameters, and subsequent calls to VW North America HQ only elicited the same canned response.

  • avatar
    DIYer

    At every oil change interval, pour half a can of Sea Foam into the brake brake booster vacuum hose. Rev the motor, there will be lots of white smoke, and then turn the motor off and let it sit for 10 minutes to soak in. Then drive the car hard for 5 miles until the white smoke goes away. This will clean most of the carbon off the intake valves. Pull one of the plugs to see if carbon has been deposited, and clean the plugs as necessary.


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