Piston Slap: Earth Dreams of Carbon Buildup?

Sajeev Mehta
by Sajeev Mehta
piston slap earth dreams of carbon buildup
TTAC commentator KCFlyer writes:

Dear Sajeev,

I have a 2015 Honda Fit LX manual, purchased new. From day one I noticed a slight momentary hesitation under moderate acceleration when the engine was cold. I took the car to the dealer after a few weeks but they could not duplicate the problem. I dropped it off again and left it overnight, hoping a cold engine would allow them to experience the issue. No luck.

Fast forward 57,000 miles. Same problem persists and is reported to dealer via phone several times. The check engine light comes on. Dealer says the code means an #3 cylinder misfire. They say the fuel injectors are clogged and charge $1,300 to replace all four injectors. Honda of America throws in $1,000 of goodwill money because fuel injectors are not covered by the 60,000 mile powertrain warranty.

Two weeks later light comes back on. Same code. This time another dealer pulls the head and finds carbon buildup on all four piston heads. They clean up the engine, clean the throttle body and declare the vehicle fixed. Total charges paid for by Honda of America under goodwill claim except $217 for the throttle body cleaning. That was yesterday and I will know within days if the original problem persist.

Tech rep was awesome. He recommends I get the fuel injectors and throttle body cleaned every 30,000 miles. My question, what caused the carbon buildup? Does the buildup damage the engine even if later cleaned up? Should I dump the Fit? It is an awesome commuter. I average 44 mpg summer and 39 winter.

Sajeev answers:

My, how this issue has changed since our first(?) discussion back in 2012: what was once a measured discussion of the merits/pitfalls of de-carboning an engine is now a second nature, knee-jerk diagnosis (that’s likely accurate).

Engines have turned into carbon cokers and oil burners, and that’s our new normal when shopping for a new ride: Honda’s Earth Dreams are no different?

The usual reason for carbon buildup is two fold: the aforementioned changes in engine design and owner’s driving style. Odds are if you rung that little L15B1 out to redline on a regular basis in lower gears (so you won’t get a speeding ticket) the modern direct injection setup would run clean as a whistle: no need for any preventative maintenance? Of course, the Best & Brightest have the final say.

But I like those shift-yourself Fits and you should keep it…preferably near redline in 1st/2nd gear just for fun.

[Image: Honda]

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.


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  • F1tifoso F1tifoso on Aug 04, 2018

    Carbon buildup is caused by the carbon in fuel backwashing - it is a design flaw they didn't foresee (starting with AUDI's DI engines) >port injection was largely self cleaning (except cheap gas left deposits) while direct injection has caused this problemever since (Audi recommendation to keep it clean? Take it to redline once a week...) a few newer systems have solved the problem with flow analysis while others now have both port and direct paired fuel injectors which prevents the problem as well (they use the DI for efficiency and port for power, allowing smaller DI injectors - of course twice the injectors = $$...) To fix: You can buy DI cleaner spray for about 3-4x the price of plain carb cleaner, and it is about 20x more concentrated (have tested both on the gunk and it is very effective) and spray off the polluted intake etc. I don't believe the pistons carbon are a DI problem, that's a tier 2 fuel problem.

  • Gearhead77 Gearhead77 on Aug 08, 2018

    Just run it hard once in a while. I'm fairly sure a trip to WOT once in awhile isn't killing anything, including mileage. .1 mpg to keep the carbon away and large repairs? A tank of premium Tier 1 fuel every once in awhile? Cheap to me

  • MaintenanceCosts This looks really surprisingly different from the Blazer EV. It's more boring, but it's also more Honda, and for that reason alone it will be taken a lot more seriously in US markets.
  • ToolGuy I found this interesting; you might too: https://youtu.be/asb4jLWWTbQ
  • SCE to AUX Q: "How do you fix automotive media?A: The same way you fix the auto show.That is to say: Don't live in the past, believing every story is original with you. Offer something insightful and useful to your audience that they can't get anywhere else.The auto show allows consumers to sit inside many vehicles under one roof, without sales pressure - something unavailable anywhere else. That's it. The media should accept that the auto show offers nothing new for them anymore, and the auto show should stop pretending that it does.Good examples:[list][*]I've flamed Posky many times, but his long background stories can be thought-provoking and informative. I may not always agree with some of the posturing, but at least they dig deeper than someone's press release.[/*][*]Alex on Autos has some of the best video reviews. He wastes absolutely no time getting to the substance, and his formula is reliable. He packs a lot into 25 minutes.[/*][*]Everyday Reviews: This likeable couple/family covers the daily life aspects of new cars they test - child car seats, user interface, fuel economy, and so on. No hype - just useful.[/*][/list]Bad examples:[list][*]DragTimes: In a 20-minute video, you get 1 minute of racing and 19 minutes of bromance talk. I keep hoping it will improve, but it doesn't.[/*][*]Road and Track's web page is heavily tilted toward unaffordable niche sports cars and racing, with a few feature articles on daily drivers. I visit, but it feels like I'm in a Porsche dealership.[/*][/list]
  • BSttac Honestly automotive journalism is all but dead. Its mostly bloggers with a left based agenda. Cnet and the Drive especially had some really horrible bloggers. Road and Track also has some terrible bloggers so it would not surprise me if they are next. Just look at most bloggers complain about going to an automotive show when they dont realize its not even for them. Very spoiled and out of touch individuals
  • Jkross22 I forgot to include Bring a Trailer. It's so enjoyable to revisit cars from different eras and to read what the most knowlegable have to say about those types of cars.
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