From: csr684@NOTyahoo.com   
      
   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.   
   >   
   > I will have this done every 50K so it never gets real bad.   
   >   
   > Shame on Mazda for using direct fuel injection. :-)   
   >   
   >   
   >   
   > Andy   
      
   A much more common and easy way to remove the carbon is to use a walnut   
   blaster. It blasts the carbon off and uses a vacuum to pull the blast   
   media and crud away.   
      
   The issue with GDI is like Xeno said, no fuel ever hits the back of the   
   intake valves so it doesn't wash them or cool them.   
      
   One thing that does help a lot on them is to add a catch can to the PCV   
   system if possible. That routes the crankcase vapor and oil out through   
   a separator so the oil and vapor can cool some and settle out of the PCV   
   return flow instead of going inside to stick to the valves, That can be   
   cleaned out during oil changes and will reduce the build up a lot, I   
   have seen it drop by over 75% on many vehicles depending on their age   
   and design. Even the smaller cans help. I've used the Evil Energy style   
   on a few vehicles and it seems to work OK, not as good as some of the   
   cyclone and fully baffled units but it's also not as expensive by a long   
   shot.   
      
   --   
   Steve W.   
      
   --- SoupGate-Win32 v1.05   
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