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I posted this on another forum had didn't get a good response.
With all this talk of DFI intake valves gunking up, I saw this Porsche graphic a while ago which shows fuel being sprayed directly over an opened intake valve. If this is accurate, it appears Porsche figured this problem out.
I find it odd that the valve is left open when the gas is sprayed.
I don't have an answer. I just use Chevron Fuel System Cleaner with Techron one tank of fuel prior to each and every 5,000 mile oil change. And don't fret about these sorts of things. Oh, and quality fuel (93 octane) from a busy station.
Fuel treatment doesn't help clean valves if it's injected directly into the cylinder. It only works when it's injected at the intake.
Most modern DFI engines use two sets of injectors: high pressure direct fuel injection into the cylinder for power/efficiency, and low-pressure injectors in the intake to cycle some fuel through the intake to keep the valves clean. Though I haven't heard them talk about it much (and can't comment on how exactly they program it), Porsche's parts catalog does show two sets of injectors on DFI engines, one each high-pressure and low-pressure per cylinder. Anyone have a paragraph from a technik talking about this?
Anytime the fuel/air mixture contacts a surface, be it a valve or piston, or cylinder wall, there is "wetting". Wetting reduces efficiency, and DFI eliminates wetting of the intake manifold walls, hence the efficiency gains.
I don't think they would "aim" the injector at the valve, and the illustration is 2D and looks that way, but in reality it's not.
... I saw this Porsche graphic a while ago which shows fuel being sprayed directly over an opened intake valve. ...
This was long (years) posted on this forum. A single injector per cylinder and yes, as the graphic shows, the injector washes out the back of an open intake valve. Weissach knows their stuff.
Fuel treatment doesn't help clean valves if it's injected directly into the cylinder.
Most modern DFI engines use two sets of injectors: high pressure direct fuel injection into the cylinder for power/efficiency, and low-pressure injectors in the intake to cycle some fuel through the intake to keep the valves clean. Though I haven't heard them talk about it much (and can't comment on how exactly they program it), Porsche's parts catalog does show two sets of injectors on DFI engines, one each high-pressure and low-pressure per cylinder. Anyone have a paragraph from a technik talking about this?
I was not aware that Porsche was using two sets of injectors in their DFI engines. I had only seen this on some Toyota and some new VW/Audi engines.
This was long (years) posted on this forum. A single injector per cylinder and yes, as the graphic shows, the injector washes out the back of an open intake valve. Weissach knows their stuff.
This still does not clean the intake port area which can become a real problem.
Not odd at all. Injecting the fuel while the intake valve is open encourages better fuel/air mixing. The injector can be triggered multiple times too so the fuel is not injected all at once but over a span of time.
LexVan has the right approach, imho, though I think Techron every 5K miles is a bit too often, maybe.
08-30-2014 | 11:14 AM
Do DFI engines clean their own valves?
