possible vacum leak

[96firebirdgt]

Does anybody else know what would cause the oil fill cap to have a vacum when the engine is running?
The car does have a miss in cylinder 4 but i am in the process of fixing it.

[lizzardfire]

I thought that there was supposed to be a slight vaccuum at the oil fill cap with the engine running?

[96firebirdgt]

I just wanted to make sure this was normal since my other cars do not do this.

Can anybody else back this up?

[peeeot]

I've never checked one way or the other, not having tried to remove my oil fill cap while the motor was running, but I know that when the motor's running the pcv valve is sucking crankcase vapors in and circulating them into the intake stream. As long as it is sucking faster than the gasses are being produced, which it probably should be, then you'll have some suction. On the 3.4 the pcv is mounted on the same valve cover as the oil filler too, so there may be more localized suction there.