Fuel system clean / direct injection

[brillo]

So now that folks have some mileage on these engines is anyone experiencing carbon buildup ala the VW audi direct injection engines?

my cx5 has 30k and I'm not sure if it needs a good fuel injection treatment, mileage seems down a bit even though I've replaced the air filter, checked tires and changed oil.

 

[GAXIBM]

I have 38000 miles on a 2013 GT 2.0 FWD and just returned from a 1000 mile trip to FL. At 72 mph I get over 33 mpg which has improved slightly over time. I normally use Pilot regular gas and keep the air pressure at the recommended 36 psi.

 

[V8toilet]

33,000 mile here and my mileage and acceleration is better than ever.

 

[MikeM.]

So now that folks have some mileage on these engines is anyone experiencing carbon buildup ala the VW audi direct injection engines?

No, and you can bet we would have heard about it if it was an issue. My impression is that the CX-5 direct injection technology was engineered to avoid carbon issues.

my cx5 has 30k and I'm not sure if it needs a good fuel injection treatment, mileage seems down a bit even though I've replaced the air filter, checked tires and changed oil.

I would suspect a small change in driving style first (shorter trips, less awareness of slowing traffic ahead leading to more brake usage, or, simply slightly higher freeway speeds due to weather conditions).

If it's not a slight change in driving style, I would suspect oxygen sensor drift (due to sensor aging) or some other electrical change before I would suspect carbon buildup on the valves.

 

[CC58]

Fuel system cleaners work on port injection, but not direct injection. Reason being direct injection collect hard deposits which cleaners have no effect. Some, not all, direct injection vehicles develop hard deposits on injectors. So far, no one has reported it to be a problem with CX-5. Oxygen sensor age can reduce mpg, but usually isn't a factor until after 60,000-80,000 miles.

If hard deposits were a factor in the CX-5, I know of an old mechanics trick to clear it out. Rev engine high while spraying a fine mist of water into intake. Water raises the combustion temperature and burns out the hard deposits. Works on an old chevy 350, not so sure with these new high tech engines. Wouldn't try it until car is out of warranty.

 

[Kedis82ZE8]

Oxygen sensor age can reduce mpg, but usually isn't a factor until after 60,000-80,000 miles.

That is usually about the time mine die and are replaced.

 

[deuce_WI]

I think the OP is talking about dirty gummed up intake valves. It's something that's inevitable with DI. As long as emissions systems like the PCV / EGR keep dumping crap back down the intake, it's going to happen.

On older port injected systems, the injectors sprayed fuel in the intake ports, which sprayed the fuel over the intake valves which constantly cleaned your valves. Move the injectors into the combustion chamber, and now you've lost that cleaning action.

Like CC58 mentioned, spraying water / meth over the valves can help clean them, but unless you're doing it all the time I doubt it's going to do much.

The only effective way to really get your valves clean again is to pull the intake manifold and use a strong chemicals, picks, brushes, and a media blaster to clean them.

Now the question becomes, at what mileage would Skyactiv motors benefit from a valve cleaning? 30k, 60k, 90k? Has anyone with significant mileage ever pulled their intake manifold to see how bad they've gotten.

Attached some delicious looking pics from another DI Mazda with about 100k on it at the time.

 

[V8toilet]

If hard deposits were a factor in the CX-5, I know of an old mechanics trick to clear it out. Rev engine high while spraying a fine mist of water into intake. Water raises the combustion temperature and burns out the hard deposits. Works on an old chevy 350, not so sure with these new high tech engines. Wouldn't try it until car is out of warranty.

I know of someone who did this to their engine and when I tore it down to rebuild it a found one of the connecting rods very slightly bent and the cylinder walls were glazed pretty bad. With an engine as expensive as the Skyactiv and a 13-1 compression ratio I would say from my experience that this is a very bad idea. Carbon deposit buildup was a problem for some early adopters of direct fuel injection but I think manufacturers have learned how to design these engines now so that carbon buildup isn't a problem like it used to be.

 

[CC58]

V8toilet posted this link some time ago I just stumbled on.
Mentions valve carbon build up was only a problem on early GDI systems and now not a problem.
https://www.youtube.com/watch?feature=related&v=IzXeeCiSL7k&app=desktop

V8toilet orginal post.
http://www.mazdas247.com/forum/showthread.php?123831195-Direct-injection-carbon-buildup-on-intake-valves-could-be-thing-of-the-past

Info from link in original post.
http://www.motoiq.com/MagazineArticles/id/2105/pageid/3529/131-compression-and-40-mpg-on-87-octane-fuel-introducing-mazdas-skyactiv-technology.aspx

"To eliminate the problem of intake valve deposits that plague current direct gasoline injection engines, the engineers at Mazda determined that deposits are formed when intake valve temperatures fall below 400 degrees C. Measures were taken so that the intake valve would operate above this point to reduce deposit formation."