Quote:
Originally Posted by DWBOX2000
So the rough running when oil cap off means nothing?
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The intent of the oil cap "test" is to check the relative amount of vacuum, not how well the engine runs, when removing the oil cap.
A good AOS will be somewhere in the range of 4"-7" of vacuum whereas a failed AOS will be in the range of 9"-12+". Thus, one way to check the AOS is to remove the oil cap with the engine running to see how hard the vacuum makes it to remove the cap.
The general saying is that you should be able to lift off the cap with a little pressure on a good AOS and it would take a good pull to get it off on a failed AOS (due to the greater vacuum that occurs when the AOS fails). The problem with this test is that it is somewhat subjective and can be hard to tell the difference between the higher and lower vacuum levels - a little pressure to you might be a good pull to me or vice versa.
This is why I suggested checking the oil vapor return hose. If the AOS is failed, then there will be a lot of oil vapor going into the intake.
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