GDI engines suffer dirty intake valves?

[Piwoslaw]

Diluting oil with fuel isn't just a GDI problem - Euromodder is fighting with the same thing in his turbodiesel with DPF.

[mechman600]

Common rail DPF diesels often suffer from fuel dilution because aftertreatment fuel dosing is done in the cylinders. Fuel is injected on the exhaust stroke to push it straight into the exhaust to react with the catalyst. Some of that extra raw fuel in the cylinders tends to get into the oil, especially during short commutes where frequent DPF regeneration is required.

[Arragonis]

The Mitsubishi GDIs from the mid-90s (the Charisma, "some cars have it, some need to be called it") and some Shoguns are noted for needing to be de-coked every 50-60K miles. It was thought to be due to higher sulphur content in fuels sold in Europe (especially the UK) vs those used in Japan.

[cRiPpLe_rOoStEr]

Some Diesels have an auxiliary injector tip at the DPF body, that's the best way to overcome fuel dilution in oil.

Originally Posted by RobertISaar

EGR isn't likely to be an issue or contributor for this problem.... most engines these days don't have EGR valves, instead VVT is used to change cam timing around so that when the piston starts it's downward motion for the intake stroke, the exhaust valve is left open enough to draw in exhaust gasses with the fresh air charge, essentially an internal EGR mechanism.

External EGR systems lead to carbon deposits at the intake manifold, therefore they still suck

[some_other_dave]

The current-generation MINI Cooper S models have a well-known problem with carbon deposits in the intake ports and on the intake valves. Walnut shell blasting is used to remove the deposits when they get bad enough.

Fuel dilution, however, has not been a problem that I have heard of.

Fitting an oil catch can and re-routing the PCV system to it has been used as a way to avoid the problem. I don't know if it is a complete solution, though.

-soD

[pete c]

You know what's worse than gummed valves and diluted oil?

Mongs who use apostrophes in the plural form of a word. It's a pet peeve of mine. I can let it slide in cases where the poster is from a country where English is not the mother tongue, but, I have witnessed it in this thread by an Englishman.

Shame on you sir for having to have your grammar corrected by a colonist.

Rant over. On to the topic at hand.

It appears that GDI may not be ready for prime time. Maybe they need to go back to the drawing board. Maybe it will never give enough benefit to justify its use. As for diesels I am very leary of the latest treatments. I think "clean diesel" is likely a good idea, but all this other exhaust wizardry has brought us such gems as the last few renditions of the powerstroke which make the old GM 350 diesel look good.

[Miller88]

Originally Posted by some_other_dave

The current-generation MINI Cooper S models have a well-known problem with carbon deposits in the intake ports and on the intake valves. Walnut shell blasting is used to remove the deposits when they get bad enough.

Fuel dilution, however, has not been a problem that I have heard of.

Fitting an oil catch can and re-routing the PCV system to it has been used as a way to avoid the problem. I don't know if it is a complete solution, though.

-soD

Most of the crap that gets stuck on the intake valves is a result of the PCV system.

I wonder if we'll see the water / steam based de-carboning come back? I'd be afraid of a piece of carbon scratching the cylinder wall or getting stuck on a ring or something.

Hmm.

Glad neither of my engines has DI!

[cRiPpLe_rOoStEr]

Originally Posted by some_other_dave

Fitting an oil catch can and re-routing the PCV system to it has been used as a way to avoid the problem. I don't know if it is a complete solution, though.

Some folks just delete the PCV and put a filter at the crankcase breather, but we might remember the unburnt oily vapors are less harmful after the combustion, so getting a PCV filter to retain heaviest fractions of these vapors is still more responsible.

[user removed]

I would suspect based on experience that PCV by itself might not be a problem as long as there is no recirculation of EGR. My 1976 280Z came factory without an EGR valve (only 75-76 Federal versions). It had a sight stain in the intake manifold from the PCV fumes but no accumulation of "grunge" that accompanied those later engines where PCV and EGR were mixed. When mixed the grunge was substantial with accumulations from the EGR ports to and including the intake valve stems.

It was one of the reasons why I liked the 1976 model above all the others. It had no catalyst as well as no EGR, the fuel injection solved the emissions problems during that short period of 2 years (Federal version only, Cal had a cat). With the later .75 OD 5 speed tranny and flat top pistons that brought compression readings from 160 PSI to almost 200PSI with the factory 3.54 rear axle.

Maybe the fuel injectors spraying onto the intake valves kept that area clean versus DI that would not. Maybe synthetic oil would help alleviate the situation which must be oil cooking on the intake valve head and stem, but that old 76 Z intake was lacking of any residue anywhere, while the next year (1977) had grunge all over the intake tracts when it got some miles on the car.

regards
Mech

[cRiPpLe_rOoStEr]

I never had to deal with any PCV-related problem, EGR is always the trouble-source.