Got a question on a '96 F250 w/351 PCV system. I believe everything is routed correctly and I've replaced the small filter in the air box. When I pull the oil cap off at idle it makes a pretty good swoosh and is pulling in allot of air through the fill cap. With the fill cap on the tube going to the air box has about as much suction as I'd expect. The suction when you pull the fill cap is surprising though. Is this normal or should I look at PCV valve? I noticed this after changing the oil several weeks back and then checking for blowby. I'm not sure I'd ever pulled the oil cap off with the truck running before. I've searched on here and the web and answers are all over the place.

 

If you are having a big vacuum pull thru the fill cap, that would tell me the vent system is plugged up somewhere. You really should not be pulling a measurable vacuum on your crankcase if it is vented properly IMO.

 

I've read that the PCV valve can be a job to replace on these engines because it's sandwiched between the valve cover and the intake. I've looked at were it is but not really studied on it. Is there any truth to that? I've read everything from taking the upper intake off to just pry it out with a screwdriver. It'll be several days before I can look at it so wondering.

 

On a factory EFI truck the PCV is mounted on a rubber hose elbow on the passenger side back of the engine. That rubber hose elbow attaches to a plastic elbow that is inserted into the valve cover with a grommet. It's not that tough to get to the PCV, but then you find out the rubber hose is dried up/cracked and the grommet in the valve cover is also dried up and shrunk. So now your simple PCV replacement project gets bigger to replace those aged pieces.

For reference, lower right in this PCV system diagram:

 

Thanks for the pic. I get why there's so many horror stories now. So far I haven't found any bad hoses on this rig but you know how that goes. I'll plan on it not being a 10 minute job but hope for the best.
I knew the basics of a PCV system but never really studied how the valve works. After some research I think the valve may be stuck or have a weak spring. I'm going to replace it either way.