Piston Slap: A Solution to our Coking Problem?

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. from The Truth About Cars http://www.thetruthaboutcars.com

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