If you have, or plan to remove carbon buildup from the back of the intake valves, did you do it before or after any codes showed up?

 

The valves would have to be REALLY messy to get a code. I suppose you might get air flow related codes (MAF and/or MAP sensors, or some more general code) or possibly fuel trim codes?

It's mostly a matter of restoring lost engine power, and is a maintenance procedure rather than a repair. I would try to schedule it along side a valve adjustment, as both jobs require removing the intake manifold.

 

@Gekisen If "before" means regular maintenance, then I do it before. My colleague @bobski is probably right.

1) Use top tier fuels.

2) Change your oil and oil filter frequently.

3) You could run the occasional bottle of Techron. I may do one at 100k mi.

4) You could clean the throttle body with a soft toothbrush and some carburetor cleaner.

 

I agree with above.
After 6 years of exclusivly running prem fuel and 6 month oil change intervals, I have yet to have this procedure done on my Fit.
Maybe it's overkill, but if it keeps me from having to do the cleaning procedure, I'm all for it.

 

Since the GK5 direct injection engine is so susceptible to carbon buildup, chances are the injectors fail long before the valves do.

So your most likely code is p0420, raw fuel being dumped into the cat. That's the hallmark of injector failure.

When my 2016 LX threw that code at 88K, that's exactly what happened. Injectors replaced under extended warranty to 150K.

 

I don't think premium fuel will help much. Shorter oil change intervals should.

The root cause is oil vapors from the crank case entering the intake system (by design, that's what the PCV system does). The vapors are supposed to get burned off in the cylinder, but some portion sticks to the back of the hot intake valves and gets converted to a carbon solid by the heat. Since there's no gasoline in the air flow over the valves, the carbon builds up over time.

Engine oil produces the most vapors at the end of its useful life, when stabilizing additives and detergents have been used up. Changing the oil before that happens should reduce vapors, greatly extending the time between induction cleanings. Oil changes every 3500-5000 miles is reasonable in my book. The maintenance minder's interval is considerably longer than that, though it's supposed to be dynamic - based on engine load and such.

 

Good advice from everyone. But you also have to blow out the carbon at least once a week. When getting on to the highway it’s 2nd and third to redline. A CVT won’t do this as well as a manual transmission.

 

My apologies. I forgot that this was the 3rd Gen Forum. You guys have direct injection. Different ballgame.

 

I cleaned the top of the valves last summer before any code shows. I already had the intake manifold and valve cover off to replace the VTC actuator spring. I do not have a walnut blaster, I used straight up non-chlorinated cleaner by Gum-out along with a ton of automotive cleaning towels + long picks. It's not completely clean but I got most of it. It cost me maybe just $40 total in cleaning supplies and parts.

You also should install an oil catch can to minimize oil misting back into the intake tract from the PCV valve. But I still had a puddle of oil that dumped out of the intake manifold.

I shortened my oil change interval to 5000 miles and do not ever follow the maintenance minder, and that's every 3 months.

 

I think cleaning the carbon deposits is more like an unnecessary optional job - like lifting up the carpets and cleaning under them.

An effective cleaning is expensive and of questional value. Use Top Tier gas.