Carbon buildup on all valves for 2009 Mazda cx7

[AK]

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.
He plans on cleaning using WD40 and a brush.
Is this a common problem?

Thanks.

[Xeno]

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)

[AK]

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

[Steve W.]

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.

[Xeno]

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.

[Scott Dorsey]

Xeno <xeno...@optusnet.com.au> wrote:
>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.

Same thing happened in the seventies. Car manufacturers did all kinds of
crazy things to meet the new emissions standards until they figured out
how to engineer closed-loop injection systems... and when they did they
found it was a win for performance and reliability as well as emissions.

I am betting the super-lean modes turn out to be a win in the long run
once the manufacturers figure out how to do things right.

>Wait until you see HCCI/CAI rolled out - that will be interesting.

I would not be surprised to discover that is the real way to do things
right. We'll find out soon enough.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."