I have a theory and would like some conversation about it.

I ran it by cornercarver this am but he started sputterin' and backfirein'(like his L does). We all(?) have found traces(or more) of oil in the intake boot, throttle body and plenum. Some have found it on the intercooler when the s/c has been removed for other reasons.

I can only think of 3 sources for this: 1. from the tube that connects the left cam cover to the boot 2. from the PCV system that is connected to the plenum(from the right cam cover) or, 3. excessive blowby past the rings and back up thru the intake area. I don't think it's from #3 because many of our engs. are still low-mileage and shouldn't have 'worn' cylinder walls.

So, many of us have removed the boot-tube, plugged the hole(thank you cc) and put a breather filter in the cam cover. I also put an oil breather on in place of the oil cap. Guess what? I still had oil in the throttle body(runs down into the boot when the eng. is off). I think I can stop this but I won't go in to that yet.

My theory --I think some of this unwanted oil is being forced into the combustion chamber along with the 'wanted' air. I think that this 'diluted' air/fuel charge can be 'a' cause of detonation or at least, be a part of the cause. Am I full of it or is there some merit to my uneducated 'theory'? I'll add this(even though it may bebunk my theory): I've never heard my eng. detonating but I worry that it may.

Dan

 

I would try a filter on the suction of the lines connected to the valve cover...if I was concerned.

 

I would try a filter on the suction of the lines connected to the valve cover...if I were concerned. Make it a loose media...or very pourous so the oil can coalesce and drip back in the valve train...just a thought..works on My turboed cars....running 17# of boost. I don`t think you will eliminate the accumulation unless you disconnect all the vacuum lines from the valve train. I wonder what effect the boost dump\by-pass has on this phenomenon.
Seems like it would recycle oil as well. Perhaps this recyle will take some time to clear out..or must be cleaned . Other wise the boost,vacuum may push it around along time.

I haven't looked in My 01's intake yet. I know I had oil in the last 99. Not to mention all the cooolant and sludge from the mixture of same. I have noticed that the couple times I hit the dump before I disconnected it that the motor was on a hell of a vacuum. Didn't die but I had to put it in neutral to get the valve closed.....This has got to draw a hell of a vacuum on those hoses. I wonder what the collapse rating is on them.

I also would like to find out just what type of valve is in the boost solenoid configuration. Gate,Ball, or needle and seat.

 

I put a catch can on the line leaving the pcv going into the upper intake. This has pretty much eliminated all the oil in the intake. I tried the breather on the driver side valve cover but I still was getting the oil. Using the catch can it will collect about a tablespoon a day. I've only had this setup a week so I've been checking it daily. I have autotap so I did some logs before and after, and the WOT O2 readings have richened up a little after the catch can, so you theory of the oil diluting the af ratio may be correct.

Also, on the stock passenger side pcv setup a hose leaves the pcv at valve cover then goes to a T where one hose goes to upper intake and one goes to lower intake. Does anyone know why one goes to lower intake? Is it to vent some boost into pcv system in order to close the pcv valve under WOT?

 

superwalker


I need to look at the T to understand why it's there. Could it be to equalize pressure above and below the intercooler.

It may backwash the bundle. Or like you say.....

 

We're hearin' from Alabama tonight--thanks guys.

Another(oh no!) thought.........we(some/most?) use 5W20 oil--'light' viscosity--wonder if it froths more in the pressurized crankcase and therefore, produces more air-borne droplets? I use a syn. oil and I would think that its characteristics would cut down on that? Would the guys that are using mineral-based oils get more unwanted oil in their intakes than the ones that use a syn. oil?

Still wondering about my 'detonation' question/theory--I know, superwalker, you touched on it but maybe we'll get some more ideas too.

Dan

 

Dan, I discussed this with Gforce a while back, and we decided that an industrial filter from an air compressor would filter out about 99% of that oil that is being sucked/blown into the throttle body.

You would just mount it onto the fenderwell or somewhere else convenient, and run the PCV lines to and from it. Since it would be a sealed system, it wouldn't set off a code in the PCM.

They are relatively cheap (about $35), and should be very effective. Just make sure you follow the arrows to get the flow direction right.

Yes, oil in the combustion chambers WILL cause detonation.

superwalker, I hope there is a check valve in the hose that goes to the lower intake manifold, that only opens under vacuum. If it leaks, you will get boost pressure into the system.

 

The oil mist mixed in with the air should make you actual O2 less dense, this would make it less likely to detonate right. However the breathers that you are talking about that have been installed in place of the vacuum lines are letting unmetered air into the engine and this could be a cause for detonation, the MAS doesn't see it so it doesn't add any fuel for it. In the summer it may not be as easy to hear because of the humidity and warm less dense air.

 

The T that I was talking about is there from the factory. Its not something I added. If you go look on the hose that leaves the pcv, it will lead to this rubber T.

Btw its superwaker not superwalker.

 

Sorry superwaker. Anything that is hooked into the lower intake will see boost when the throttle is opened, and high vacuum when the throttle closes and the blower bypass comes into play.

When you close the throttle, you want the vacuum to draw the crankcase gasses into the intake to be burned during combustion. With the engine under boost, the intake cannot draw in the gases, so they use the next best blace, which is the intake boot. There is a pretty good vacuum there when the blower is in full song.

 

Dan us LS1 guys have had the same problem with turbos. The boost pressurises the engine thru the pcv valve. To solve this I installed a check valve......a GM brake booster check valve I had, inline with the pcv. This solved the oil prob for me. The oil also lowers the octane rating of your a/f mixture which of course can cause detonation.

 

Boy, this problem sure sounds familiar.Back when I had a 70 Z28, I took off the alum valve covers to have them polished.When the polisher looked inside of them he asked what the small tinny 2inch by 2 inch raised "table" looking peice was that was under the PVC opening. Well as you could guess it was a baffle so oil would not directly hit the PVC valve. Later when I spoke with the Chevy parts guy about this, he told me the earlier Z's didn't have this and they were finding oil in the intake !! I haven't pulled off the left side valve cover off the Lightning ..but I wouldn't be at all surprized if there wasn't one on our trucks. Seems like one could easily be fabricated if that was the case. Sometimes the answer lies below the obvious.