How to keep valves clean in a direct injection eng

[Laminar Lou]

Okay, so in a typical multiport injection engine the fuel and air mixture enters through the intake valve. Therefore the fuel and fuel detergents can keep the valves clean. This is my understanding, correct me if I am wrong:

1) Most intake deposits are formed from oil/vapor/muck returning from the PCV.
2) A smaller amount of deposits are from the air.
3) An even smaller amount of deposits are from the gasoline itself.

So if I my fuel isn't touching the tops of the intake valves anymore in a direct injection engine how do you keep them clean? Or is this not a legitimate concern (maybe my above 3 assumptions are incorrect)? I would think Diesels would have this same issue, right?

 

[forcedtalon]

How is the fuel not touching the valves? The injector is on the intake runner way before the valve to get mixed with the air.
You keep a good synthetic oil in the motor you wont have any depsosits left of the valves from the PCV.
Lucus USL that is used in fuel is oil based and is desighned to keep the entire fuel system clean.
A properly working PCV will also keep the intake cleaner since its not open all the time letting excess oily vapors into the intake track.

 

[kcryan]

Direct injection sprays right into the cylinder is what he means.


I'm just guessing, but i would figure every 50k or so mabye some seafoam or something similar? it wouldnt seem to be needed as often on these cars

 

[JTK]

Good question LL. You would think a DI engine would tend to dirty up the backs of the intake valves more since there is no fuel to 'wash' away the blowby junk. Kinda like the 'dry intakes' on port injected engines. Oil just pools instead of being washed through the nooks and crannies of the intake manifold.

Joel