Crankcase Vent Valve - D-Jet Vacuum Leak

[vwduud]

Very nice. Thanks Brad.

[raygreenwood]

No it wasn't a problem with excessive blowby. It was my last engine with 20k miles on it. It probably had to do with the hose routing. When using the pcv valve in the stock location on a 412, it routes to a specific fitting on the air cleaner where it draws from the air cleaner and goes through the heads first. If you try to reverse that and dump into the air cleaner, you have to use a different fitting (the lower one that normally goes to the charcoal filter). The top one has a one way baffel built into it and heat sealed into the air cleaner case. If you try to use the top one on this air cleaner...the back pressure will blow the valve cover gaskets loose. The engine was at 102 hp and saw a lot of high revs. It also had the correct vent lines to both valve covers. Thats where he oily mess comes from when you reverse the lines o a 1.7 and some 1.8's. I don't think I have ever driven a car that burns oil. I am a fanatic about that. I rebuild before things get expensive. Changing the routing was in response to the problems I experienced with the PCV valve and the MPS. Throttling it to 3mm orifice and going back to original routing fixed everything. The oily mess problem with vented rocker boxes is the reason why they put a non reverse flap in the air cleaner...so you could not reverse the lines. You also would not have that air cleaneron most 914's. Its te round one with pleated filter.
I also found that when reversing the lines and the PCV flow, since there was no vacume per-se from the air cleaner connection, the pressure in the crankcase had to build up higher in order to unseat the spring in the PCV. It vented less often and at higher volumes and pressures. It caused a larger upset to the MPS when it did. That would also depend onhow you are tuned at the MPS as well. Ray

[914turbo]

Many thanks to all!!! This thread clued me in to several potential sources of drivability issues on my turbo'd teener. Now let's reaaly throw in a monkey wrench! My 2.0 has a (Crown/Rayjay) turbo and the pcv valve is T'd (actually a "y") from the PCV valve to the air cleaner (from a Corvair turbo) and back to the Aux air valve. How will the PCV valve behave (assuming it is working properly) under boost / positive manifold pressure? The line leading to the air cleaner after the "y" was pretty oil soaked but the air filter element and housing wasn't oily. I did notice that the intercooler has some oil in it, and I'm wondering if the PCV line hooked up to the air cleaner might have something to do with it?

Rob

[raygreenwood]

Lets see if I have your routing straight in my head....from the PCV..."T" comes before the air cleaner...correct?....one side to air cleaner...one side going between the aux air reg and the manifold?...correct?

I would bet that the oil in the line that goes to the aux air valve is there becase that is the only side producing considerable vacume. The air cleaner produces very low vacume which is why they didn't originally route it into the air cleaner. Try this....clamp off the air cleaner line and see if it makes any difference. My bet is that it won't, as most if not all, of the vented gas is going to the manifold side of the "T". Its flowing to the path of least resistance. Or in this case the path of least atmospheric pressure.

I'm guessing here, but if you have enough blow by to overcome the original oil baffel in the stock air box and put oil into the line....then chances are, the relatively weak spring in the stock PCV is staying open all the time. If you are running well, then your tuning on your D-jet with turbo has overcome any addition/changes that a full open PCV may cause. At that point...yes...I would think that you could add almost any oil baffel system that you want...as long as it is before that PCV, in relation to the manifold and not after. The only way I can think of to find out if your PCV is staying open all the time is to take an old one...use a pick to break out the small plastic disc...re-install and see if there is a change.
If there is no change...chances are...its staying open. At that point I would put in a different baffle and either delete the PCV (since you seem to be running well without it and are getting venting) or install a restrictor with a hole in it, in its place. Ray

[914rrr]

Lets see if I have your routing straight in my head....from the PCV..."T" comes before the air cleaner...correct?....one side to air cleaner...one side going between the aux air reg and the manifold?...correct?

I would bet that the oil in the line that goes to the aux air valve is there becase that is the only side producing considerable vacume. The air cleaner produces very low vacume which is why they didn't originally route it into the air cleaner. Try this....clamp off the air cleaner line and see if it makes any difference. My bet is that it won't, as most if not all, of the vented gas is going to the manifold side of the "T". Its flowing to the path of least resistance. Or in this case the path of least atmospheric pressure.

I'm guessing here, but if you have enough blow by to overcome the original oil baffel in the stock air box and put oil into the line....then chances are, the relatively weak spring in the stock PCV is staying open all the time. If you are running well, then your tuning on your D-jet with turbo has overcome any addition/changes that a full open PCV may cause. At that point...yes...I would think that you could add almost any oil baffel system that you want...as long as it is before that PCV, in relation to the manifold and not after. The only way I can think of to find out if your PCV is staying open all the time is to take an old one...use a pick to break out the small plastic disc...re-install and see if there is a change.
If there is no change...chances are...its staying open. At that point I would put in a different baffle and either delete the PCV (since you seem to be running well without it and are getting venting) or install a restrictor with a hole in it, in its place. Ray

Thanks for the response Ray!
It looks like you may have nailed the source of the oil in my intercooler!
Yes, you have the routing on the hoses correct and your theory on the flow sounds right. The existing hose routing is not stock at all, as it goes from the PCV valve , to the "y" and branches off to the air cleaner on one end , while the other goes to the aux air valve and on to a fitting on the pressure side of the turbo compressor. There are no hoses to the heads, as the breather ports are blocked off !?! What's weird is that the hose going to the air cleaner is the oily one! The air cleaner is from a Corvair turbo, and doesn't appear to have any baffles / check valves in it. Would adding a check valve or baffle to the air cleaner help? I looked inside the air cleaner hose that goes to the intake side of the compressor, and it looked pretty oily.

I do plan on testing the old PCV valve per your post and also pinching off the air cleaner line. I'm also replacing the PCV valve with a new one just for grins, to see what effect/change it might have. I'm also looking to add a breather box to the system. I posted the "breather box...djet" thread also under my regular user ID (914rrr). I goofed on this thread and used a new "guest" ID of 914turbo(DOH!)

Thanks again for the help on both threads!
Rob

[raygreenwood]

Ah...you answered it yourself... Actually, I would bet that both lines are technically oily. The one to the aux. air reg has a lot of vacume...and keeps its line cleaner...by pulling the oil into the manifold. I bet if you pulled the plenum out, you would find more oil residue than you think...and sooner or later some in the MPS. The air cleaner line just collects its oil because it does not have the vvacume to pull it in. I only speculate that you will find oil in the MPS sooner or later, because the oil bath air cleaner 411's used to sooner or later deposit the oil in the MPS. Ray