From: xenolith@optusnet.com.au   
      
   On 18/6/21 1:40 am, AK wrote:   
   > 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.   
      
   That means, since the oil isn't getting caked and baked on, you are   
   getting a *lot* of oil hitting the backs of the valves. As has been   
   suggested, get yourself a catch can arrangement.   
   >   
   > I will have this done every 50K so it never gets real bad.   
   >   
   > Shame on Mazda for using direct fuel injection. :-)   
      
   All in the name of *efficiency*, in particular fuel efficiency, and   
   Mazda are not alone. They can run in stratified charge mode at very lean   
   mixtures in cruise - up to 40:1 in some instances. The problem is - they   
   introduce a whole new raft of problems.   
      
   Wait until you see HCCI/CAI rolled out - that will be interesting.   
      
      
   --   
      
   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)