From: scientist77017@gmail.com   
      
   On Thursday, June 17, 2021 at 7:09:47 AM UTC-5, Xeno wrote:   
   > 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)   
      
   Actually my mechanic was able to remove most of the carbon.   
      
   I will have this done every 50K so it never gets real bad.   
      
   Shame on Mazda for using direct fuel injection. :-)   
      
      
      
   Andy   
      
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