Hkp7

One big question I have. I am under the impression that the crankcase has to be under vacuum, if it werent, the movement of the pistons could cause pressure. If the crankcase is vented but not under vacuum, what would this cause. Would I see symptoms of the engine fighting pressure?

Hkp7

Would be nice for Mrmerlin to chime in on this thought.

RCinXS

You said you had a check valve in the air cleaner line, Could this be installed backwards?

I don't remember a check valve on my 84 but the car hasn't been stock for years.

Also, as I remember, there is a hose that goes to the plenum on the drivers side where there is a "Y" connector shared by your brake booster. It's actually a restrictor and could be clogged up.

If car is back together, loosen the oil seperator cap leaving 3/8 inch play (you are venting the crankcase)and take for a ride. If the fighting problem goes away, you have verified positive a crankcase pressure problem. This could get a little messy, blowing oil out the separator. You could limit this by slipping a nylon stocking over the separator and wire tieing it on. Cotton sock would be better to avoid the mess, untill it gets saturated with oil.

Larry Velk

My '86 has the 'check valve'. It is like the world's cheapest PCV valve. It doesn't center well, doesn't look like it seals well either. I don't think this part could be critical, because if it is - it is way under designed. I agree with Fabio - the vent system on these cars is lame.

Opelotus

Does anyone know if the aftermarket plate which mounts under the oil fill/breather assembly to prevent oil slinging up into the vacuum lines actually works? I made a thin galvanized steel plate to be bolted on whenever I remove the assembly so junk can't fall into the crankcase, I could cut/bend similar vents in this plate and then reinstall the breather assembly over it, but would it help oil consumption or just be a waste of time?

BTW my '84S also has the PCV valve, it does seem odd that it only functions as a check valve for the airbox line, why not the line to the TB as well? Also, what's the point of the large diameter hose on the oil filler cap when the actual pcv hole in the cap is tiny?

RCinXS

I have Carl's (928 Motorsports) oil control system that includes a plate installed.

Yes, it does work.

928 Specialists also has a oil control system some of mt friends use. Also works well.

Not sure why the Porsche engineers seem to have wanted to throw oil up from crank into the oil separator.

My guess is so the oil separator would have something to seperate?

RCinXS

There is a bit more to it then just a plate.

Cosmo Kramer

One test you could do would be take all the vent hoses from the valve covers and oil filler tube and put them into a temporary catch can. Start the car and check for vacuum on the ends going to the throttle body, if vacuum is present plug them to stop the vacuum leak, if no vacuum you could have a faulty check valve or blockage. Observe the lines going into the catch can and see if the blow by seems excessive. If possible, secure the temporary can and go for a quick drive to see if the power issue is resolved.

RCinXS

Even better than the sock!

Opelotus

So will a baffle plate alone make any difference?

RCinXS

If you leave the oil separator "Basket" installed along with the plate, I believe that it would help a bit.

I think I have an new extra oil control kit from 928 Motorsports in my garage. I'll take a look if you are interested. It would be one of the original versions.

Hkp7

Sorry everyone for not getting back in the last few days, im facing divorce with children at this point. Came up suddenly. I may have a few good items for sale due to having to move to an apartment. I am staying strong and keeping the 928 no matter what even though it runs like sh&t.