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.