If any of you remember I’ve been going round and round with my intake manifold leaking and my pcv system. I think I might have found the problem.


My drivers side valve cover has a pcv valve installed in it. If I have someone else rev the truck slightly and get off the throttle in kind of a rolling idle and shake the pcv valve it will go up from its lowest resting position to the middle where it’s allowing air to go past the “plug” inside. Then it will go even farther up and completely seal off again and stick in the upward position until vacuum drops enough to let it drop down. So while I’m cruising part throttle in a high vacuum situation and that hopped up there it would stay they until I did something like really opening the throttle to get it to drop. Even at idle it’s possible to whip jerk the valve around and get it to stick. You can hear a whistling when the valves in the middle position, but letting it fall or letting it go all the way up the whistle stops. My truck makes 20 pound so of vacuum at idle and takes very little throttle to get down the road. So I’m sure that helped the situation, not.

Replaced pcv valve with another that CANT do what the last one does. Even pushing it up with a pick there’s a stop keeping it from going to far up. The whistle never stops in the upward direction. I’ve replaced my old pcv valve a couple of times, with the same valve. The new one I got from napa.

I’ve cleaned the block as best I could and have been continuing to drive the truck and the intake is leaking much less. Much less smoke from the valve cover, much less oil residue around the dipstick. No oil leaks around the breathers on the valve covers. I will change the intake seal again after watching it for awhile.

Thank you guys for all your help, information, explaining, and diagrams! You guys make it all so much easier in so many ways. My ford truck wouldn’t be in as nice of condition as it is now without this specific sub forum on this site. Thank you guys for the help in my last few intake threads, and in all of them. I’m proud to be a poster here.

 

Thank you for posting the conclusion to your problem, which started in this thread : https://www.ford-trucks.com/forums/1...9-400-a-2.html

The PCV valve reminds me of the Duraspark distributor pickups in that they can test 100% ok, but still be 100% crap.

I don't trust the PCV valves, as there's no way to test them with 100% certainty.

You might like to consider an alternative, and yeah, LOL, there's quite a choice :

https://www.summitracing.com/search/...ver%20breather

 

Before I found the new valve that couldn’t be over pressed I was gonna cut the bottom of my old valve off, take the guts out, and just run the hose out of it past the carb down the firewall and past the bell housing. Just a tube out of the valve cover. Build pressure now! Might still do that.

I was gonna post my other threads but I’ve made like 4 lol