Gasoline direct injection and oil

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Because on a traditional port fuel injection engine, the fuel sprays across the intake valve and keeps it fairly clean (when using quality gasoline with detergents).

On direct injection engines, there's no fuel keeping the valves clean and so the contaminants in the PCV gases build up in the intake and on the intake valves.
 
You'd think the valves would be cleaner... no gas touching the valve. I don't get it. Or the contamination issue. It's not diesel, it's still gas, burning less of it. so what gives?
 
Ahhhhh, thanks drew that makes sense, I hadn't though of that... That seems like it should be a fairly easy problem to fix though, doesn't it? Why not vent the PCV somewhere else? Like oh, I dunno, into the engine bay? Or something....
 
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Originally Posted By: rudolphna
Ahhhhh, thanks drew that makes sense, I hadn't though of that... That seems like it should be a fairly easy problem to fix though, doesn't it? Why not vent the PCV somewhere else? Like oh, I dunno, into the engine bay? Or something....


The common fix for DIY gearheads is a catchcan/oil separator for the PCV system. I think some OEMs use them with an automatic drain system that drains back into the crankcase.
 
Originally Posted By: Drew99GT
Originally Posted By: rudolphna
Ahhhhh, thanks drew that makes sense, I hadn't though of that... That seems like it should be a fairly easy problem to fix though, doesn't it? Why not vent the PCV somewhere else? Like oh, I dunno, into the engine bay? Or something....


The common fix for DIY gearheads is a catchcan/oil separator for the PCV system. I think some OEMs use them with an automatic drain system that drains back into the crankcase.


not only that, but add on ones are exempt from the smog inspection since they actually help emissions.
 
Originally Posted By: rudolphna
Why not vent the PCV somewhere else? Like oh, I dunno, into the engine bay? Or something....

Routing it to the exhaust is better. http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1578430&page=1 This setup pulls 0-3" Hg of vacuum so you still have vacuum evacuating crankcase gasses. For brief moments it hits 5" Hg. It also makes more power due to better ring sealing.

I changed the configuration from what is shown on this old post though. It runs off the back of the valve cover and front pcv is blocked now. Also I removed the check valve that was on the exhaust nipple. I may add a second exhaust nipple in the future to see if it pulls more vacuum. Somewhere arounf 6-7"? may be the sweet spot of increasing power but not too much to pull in too much oil.
 
This is crazy! Didn't anyone consider the SOURCE of this article?? It's somebody's freakin' idea for a patent so of course they are going to support their idea and try to prove it's needed. GM, VW and others know more about engines than this inventor and many of us here. I've yet to see any proof that Direct Injection has these issues.
 
Plenty of proof has been posted here, to include links to other forums with pics of intake manifolds removed showing intake valve completely loaded with gunk, after as little as 5,000 miles.

Do a search.
 
Originally Posted By: GMBoy
This is crazy! Didn't anyone consider the SOURCE of this article?? It's somebody's freakin' idea for a patent so of course they are going to support their idea and try to prove it's needed. GM, VW and others know more about engines than this inventor and many of us here. I've yet to see any proof that Direct Injection has these issues.


The problem with direct injection engines is well-documented. It stems from the PCV system and the EGR system.
 
The other reason why DI seems to have fuel dilution issues with the oil is because the fuel is sprayed into the cylinder directly and not across a hot valve which causes it to somewhat vaporize into a gaseous mixture or at least preheat it so that when it enters the cylinder it is almost all gaseous already or much more vaporized easier.

This helps keep it from seeping past the rings an into the oil.

It's a great technology once they refine it and find a way to deal with the PCV gases without going across the valves.

I don't like the idea of venting it (PCV gases) to the catalytic to be burn't because it will cause increase catalyst wear from the oily vapour hitting the platinum directly containing ZDDP. Also the oily residue could clog the converter.

Just not a good idea IMO. It has to be vented through the engine to be burned (pulverized) before making its way to the converter.

Perhaps through the cylinder head into the cylinder directly with some sort of check valve that closes during combustion or something.... Dunno but the current setup isn't working.
frown.gif
 
Well, I can see the points now about valves. But fuel dilution is iffy. I mean, DI gives better fuel economy and power so you'd think if fuel was leaking the PCM would be making the mixture richer and so forth. Oh well - time will tell atleast if the GM DI's like my CTS goes the same route as what G-man and others have pointed out with the other makers. I wonder if regular throttle body cleanings would keep valve deposits in check? Seems like it would since you are passing a cleaner mixed w/air accross the valves in some manner..
 
Originally Posted By: Drew99GT
In addition, several manufacturers have TSBs out discussing the problem.



No GM TSB's out yet. Maybe there is a difference in the GM system?
 
Originally Posted By: GMBoy
Well, I can see the points now about valves. But fuel dilution is iffy. I mean, DI gives better fuel economy and power so you'd think if fuel was leaking the PCM would be making the mixture richer and so forth. Oh well - time will tell atleast if the GM DI's like my CTS goes the same route as what G-man and others have pointed out with the other makers. I wonder if regular throttle body cleanings would keep valve deposits in check? Seems like it would since you are passing a cleaner mixed w/air accross the valves in some manner..


Do not forget in the USA, these DI systems run rich to avoid a lean burn situation and a subsequent rise in NOx levels. In Europe the DI is set to run much leaner under light loads than comparable USA systems. So the USA versions seem to have more fuel dilution issues, and this seems to be the case for all DI engines so far.

Browse through the UOA section, even the non DI 3.6L v6 engines beat up the oil. Especially in the Lambda platform where they work harder.
 
How about diesel engines: they have only air going past the valves.
Do diesel engines have a better PCV system?
Or a better sealing piston ring set?
 
Originally Posted By: SpitfireS
How about diesel engines: they have only air going past the valves.
Do diesel engines have a better PCV system?
Or a better sealing piston ring set?


The nature of diesel blow-by is different from gasoline blow-by. But the real culprit in both gasoline and diesel engines is exhaust gas recirculation. Modern diesels with EGR are suffering from the same problems as DI gas engines as far as carbon build up in the intake manifold and on the intake valves.

Look at this build up on the intake valves of an Audi DI engine:

DSCN3443.jpg
 
Originally Posted By: wolfc70
Originally Posted By: GMBoy
Well, I can see the points now about valves. But fuel dilution is iffy. I mean, DI gives better fuel economy and power so you'd think if fuel was leaking the PCM would be making the mixture richer and so forth. Oh well - time will tell atleast if the GM DI's like my CTS goes the same route as what G-man and others have pointed out with the other makers. I wonder if regular throttle body cleanings would keep valve deposits in check? Seems like it would since you are passing a cleaner mixed w/air accross the valves in some manner..


Do not forget in the USA, these DI systems run rich to avoid a lean burn situation and a subsequent rise in NOx levels. In Europe the DI is set to run much leaner under light loads than comparable USA systems. So the USA versions seem to have more fuel dilution issues, and this seems to be the case for all DI engines so far.

Browse through the UOA section, even the non DI 3.6L v6 engines beat up the oil. Especially in the Lambda platform where they work harder.


I've got my own UOA's (which I posted before) of my 2008 3.6DI CTS with NO fuel dilution or any issues. I'll do a search to see the others.
 
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