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Kabra

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Everything posted by Kabra

  1. I tested compression (150-160) and leak down (<9%) on all cylinders so it checks out good. That's not a surprise because the car runs great aside from the smoke bombs. I initially thought the condition only occurs at WOT but it's much more interesting than that. Believe it or not it's somehow related to engine temp. When the car is cold there is no pressure build up and the crankcase maintains normal vacuum numbers. As the engine warms up the crankcase vacuum gets smaller until it turns into pressure. At this point I'm talking with respect to WOT. Once at normal operating temp the pressure numbers go crazy like in the 30s and 40s (inH2O) under WOT. But I also noticed that (when warm) the pressure buildup occurs even under moderate acceleration. With the manometer attached I'm able to cut the acceleration when I see the pressure building so as to prevent the smoke bombs. What I describe here is repeatable and not just a one off circumstance. I'm completely stumped. Also, I have given more thought to the check valve you referred to that opens under vacuum. The only checkvalve I can find is 996 107 047 51 and that is a pressure relief valve that I gather opens somewhere about 65 - 80 inH2O. Is there something else that I'm missing?
  2. I just replaced the AOS with a brand new one from the dealer. All works well but still having smoke bombs during sustained full throttle where vacuum turns to pressure up to about 25" of water. This vehicle is a 2000 S and I hooked my manometer up to a '99 to compare numbers. Generally the numbers are comparable but I never see a pressure condition on the '99. On the 2000 S when under full throttle you can see vacuum heading toward zero and a rapid pressure buildup and then a smoke bomb when it's sustained. I have not tackled the check valve yet as I'm trying to understand how that can cause a pressure condition. I am told on later model Boxsters that check valve is eliminated entirely. Any idea what the check valve "checks" and in which direction? In the end it seems that the smoke bomb is a symptom of the pressure condition occurring at wide open throttle but I don't understand what would be causing that pressure and only at wide open throttle.
  3. Thanks for the advice as I didn't think 6" would indicate that the AOS could be suspect. It was replaced already but I've seen on the forums where new ones are sometimes defective. It seems pointless to replace it though until I track down the source of the pressure. I'll see what I can do with the PCV like valve that you mentioned.
  4. I am having the familiar intermittent smoke bombs out the exhaust but I have at least some reason to believe that it's something other than the air/oil separator. I say that because I have manometer I use and when things are normal I never see the vacuum get beyond about 6" of H20. But when it smokes the vacuum not only disappears but there's actually pressure in the crankcase up to about 25" of water (~1PSI). Yes, pressure as in the meter turns to a reading with a minus sign! I can almost cause this at will by alternating between full acceleration and full deceleration and the problem occurs during the acceleration phase. I don't understand enough about these engines to know why or how a positive crankcase pressure can be created as I gather the AOS regulates what is supposed to be a very small vacuum in the crankcase. Can someone help me out with this?
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