Apologies if this is all "old news" to many of you. Honda seems, so far, to have avoided the intake valve carbon build-up problems that have plagued some other brands using GDI engines. Intake valve deposits are caused by oil from the PCV system coating and baking onto the backs of the intake valves (in GDI engines there is no fuel washing over the backs of the intake valves to clean them). So limiting oil in the PCV fumes is obviously a key to preventing valve deposits. This is why some people install oil "catch cans" on their cars.

I discovered that the Fit has, for many model years, had an air/oil separator built into its PCV system. PCV "breather boxes" are fairly common, but the system on the Fit (and other Honda models) has a series of baffles, very similar to what are inside the best-performing "catch cans". Oil droplets in the PCV vapor stream coalesce on the baffles, and drain back into the crankcase.

I wonder if this is part of Honda's apparent success in avoiding GDI intake valve deposits?

 

My thought is that the detergent in the fuel help reduces carbon build up in the combustion chamber. That includes piston heads, valves, and the direct injectors. Direct injectors improves gas consumption over port injectors, but they can be headache when the engine starts to run rough at 30-60K miles. I suspect the cost of cleaning out the injector nozzle and maintenance does not justify the improve fuel cost savings. I am glad my earlier 911 Turbo has port injectors (less maintenance, operate cooler, last longer) and not direct injectors.

 

That was a bigger problem with early direct injection engines. I know of a few things that help newer engines avoid it:

Some engines have direct AND port injection now, so the back of the valve does get cleaned.
Valve timing can be altered to expose the back of the valve periodically. no idea how.
You can buy a cleaner you spray into the intake (throttle body) that cleans the back of the valve.

But you are probably right some manufacturers are doing something better than others to prevent the issue. Apparently GM and Ford vehicles never have issues; but there are many many TSBs and complaints about Mini, Audi VW etc.

 

 

Very very few such examples. And no one has ever claimed that Honda has solved the problem. Probably the best that Honda was able to do is push it out so that the carbon problem takes a lot more mileage before it shows up. Even the catch can solution which some have added** will not prevent the problem from happening but will again push it out quite a bit, so far that you might never have to worry about it while you own the car.

**which perhaps voids your warranty and is also possibly illegal where you live, being a tampering with the emissions system.

 

 

https://www.fitfreak.net/forums/3rd-...higher-15.html

jhass, this thread has a lot of information that may be of use to you.

 

 

 

 

jhass, yes I think you are right. Some smart engineering and the problem is solved, or at least pushed out a lot longer. I believe that early implementations of DI such as BMW/Mini they hadn't quite realized how much of an issue it would end up being, or how to solve it.

 

Here's a It's the 1.5 L Earth Dreams DOHC i-VTEC motor from our GK Fit. Notice how the injectors spray directly into the back of the valves. I'm liking that!

Edit: Actually, now that I think about it, the injectors are probably aimed between the intake valves of each cylinder...

 

wait, so I have to get on it here and there to clean up carbon build up? I don't mind that.....I remember my cousin having to floor his rx7 occasionally to clean up the carbon build up on it's seals. Gives me an excuse to occasionally get on it for a bit

 

This is exactly where you want the injector to spray, directly into the air intake path that is split between both intake valves at the end of each intake port, the di injector pulse is extremely high pressure (500ish psi at the fuel rail) and extremely atomized, the spray directly contacts the back of the intake valves as they extend. The inhalation of crank waste (oil vapor etc) through the pcv system has to go through the intake manifold just the same, so its ideal the injector is spraying right along the same point. Running higher octane, higher detergency fuel aids this purposely engineered function as you've realized.

 

It's probably only my imagination, but I've always felt my Fit drove "better", with snappier throttle response and improved fuel economy if I "drove it like I stole it" every so often.

 

I just wish I didn't have to make a 32 mile trip to find "top tier" gasoline.

 

Uncle gary order yourself up the big bottle of lucas fuel injector cleaner/upper cylinder lubricant and you can make it last a LONG ass time with our small 10.5 gallon tanks. If u cant get any top tier just stick to the highest octane u can buy, and treat with lucas every other tank. it's not the same kind of detergency that top tier fuel has, but it will go a long way in keeping these DI injectors clean and keeping carbon from wanting to stick.