From: xenolith@optusnet.com.au   
      
   On 17/6/21 11:38 am, AK wrote:   
   > After replacing ignition coil and plug for #3 cylinder, my mechanic found   
   heavy carbon buildup on all valves. The car only has 108K miles. He is   
   replacing the fuel injector and egr valve along with cleaning the valves.   
      
   The engine in those is a Gasoline Direct Injection (GDI) and they have a   
   habit of coating the intake tract and the *backs* of the *inlet valves*   
   with carbon. That is because the engine *injects* fuel directly into the   
   cylinder so the intake tract and backs of inlet valves never gets fuel   
   wash as they would were the engine carbureted or port injected.   
   What happens is the PCV and EGR system contribute to an oil film in the   
   intake system and this unburnt oil and fuel turns into carbon on the   
   backs of the hot inlet valves. It can build up sufficiently to restrict   
   air flow into the engine - which is what I presume your engine is doing.   
      
    > He plans on cleaning using WD40 and a brush.   
      
   Won't work. The carbon gets baked on rock hard and is damnably difficult   
   to shift. Look up *seafoam* which can be used to clean the carbon on the   
   backs of the valves. Note, if seafoam is added to the fuel tank, it will   
   *not* prevent the backs of the intake valves from carbon build up since   
   the fuel is injected directly into the cylinders. It will only be able   
   to clean the combustion chambers and valve faces.   
      
   > Is this a common problem?   
      
   Yes, very common.   
   >   
   > Thanks.   
   >   
   Look up carbon build up on the backs of intake valves. You will likely   
   find plenty of info and even video clips on the issue.   
      
   --   
      
   Xeno   
      
      
   Nothing astonishes Noddy so much as common sense and plain dealing.   
          (with apologies to Ralph Waldo Emerson)   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)