My son has a 1990 F150 6cyl 4.9L. He found oil in the air filter. We hope it's the PCV valve or blocked hose. We can't find the PCV valve. This is his first truck, he is 16. It was a work truck and it runs great (Except for oil), considering it has 313,412 milles on it. If someone knows the location of the PCV valve, please let me know. I would be one greatful mother of a 16 yr old son.

 

I think it should be right on top of the valve cover. If it's not there then maybe that is the reason for the oil in the air cleaner, someone may have "deleted" it.

 

It's in the valve cover towards the rear of the engine, almost impossible to see because of the EFI manifold. You may have to feel around to find it