Carbon buildup on valves

Maintenance/Repairs
21

Every thing you said is true.

And what you mentioned is being done.

Shame on Mazda for using direct fuel injection.

22

It uses 1/2 quart between oil changes.

23

Lots of (most) makes are using direct injection in some form. Recently some are using a combination of direct and port injection to prevent the buildup. Direct injection, but with a little port injection to keep the valves clean. Iā€™m not sure how that works - if a certain percentage of the fuel is injected through the ports all the time, if the pcm commands those injectors on at a certain time, or what.

24

With direct injection, a cleaner such as this should be used on occasion to prevent carbon build-up on the intake valves.

Tester

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25

Right. I forgot about that easier route to see the valves - at least the intake valves.

Is there any performance problem that the valves are causing?

26

Not at all. Direct injection give better power and better fuel economy. Plus it got you to 100K miles with no troubles.

Some manufacturers get around that by using direct and port injectors for each cylinder. Costly, but it eliminates this.

27

Yes, my mileage dropped from 20 mpg to 18.

28

Thatā€™s more likely. Good one.

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29

Are the valves sealing OK (vacuum gauge test and/or compression test)? Does the valve lash need to be checked and/or adjusted from time to time?

30

I have cleaned carbon deposits from intake valves that had 50% blockage, definitely carbon, not sludge.

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31

Iā€™m betting carbon, next to no oil consumption, direct injection, 100k miles.

32

Another method is for the engine to run hotter to burn the schmutz off during operation. IIRC, some car manufacturers, like GM, use that. Earlier implementations of direct injection didnā€™t do this, and build-up on the intake valves was a result. GM was not an early adopter and in a way, benefited from otherā€™s problems.

My repair shop uses the Sea Foam product mentioned above at the oil change in the 35,000 to 40,000 mile range to help reduce build-up. I have a 2017 Accord 4-cyl., and it is direct injected.

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33

I like Toyotaā€™s implementation of Direct Injection. Itā€™s direction injection AND port injection.

Toyota D-4S: Port Fuel Or Direct Fuel Injection? Why Not Both? - (tomorrowstechnician.com)

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