Air pressure coming out of oil filler hole

[philz87]

Today I changed my coil, plugs, wires...and I just randomly was checking to see if all the screws and caps were on tight. Its been my first chance to work on my car in a heated garage...and when I removed the oil cap, it had a lot of air pressure coming out and it made a weird noise.
There is no knocking...and no check engine lights.

What should I check first>?

~Phil

[1turbofocus]

If your talking that you had the engine running and removed the oil fill cap and you could feel a steady stream of air coming out with a little psi behind it this is perfectly normal , if you put your hand over this and slowly go down and seal off where the oil fill cap goes you will see as you seal off the hole with your hand the psi goes away

Tom

[sleepyboy]

Moved to Technical Chat

[tmittelstaedt]

this is cylinder blowby. Normally it goes through the PCV valve and onwards to the intake plenum. there is also often a vent tube from the engine that goes to the air filter airbox in case the PCV valve gets overwhelmed (I guess) and a little filter in the airbox on the end of that. Often that filter gets oil saturated and clogged and it can't hurt to check it. The open oil fil cap is a easier path for the blowby to take which is why you feel blowby coming from it when it's open.