I have an '87 4.0 that blows oil into the airbox, flooding the filter. I'm told that the CCV system is supposed to prevent that, but no-one seems sure how it works.
I took mine apart this am and had a look. There are a couple of triangular tubes located under both the small and large vacuum tubes, each one has what looks like it might be a flapper that would cover the end of the tubes under certain conditions, that I can't imagine.

Any body know how this thing is supposed to work? The flapper things in mine both seem to be bent at the same angle, and seem unlikely to ever actually close.

is puzzlement..

 

The line from the rear of the valve cover to the intake manifold has to be clear of any obstructions, including the fitting on the intake. The valve cover grommet must seal well on the plastic orifice in that line and the orifice must be clean. Carb cleaner works to flush them out in most instances.

Since it's an 87, I would surely click on the link in my signature below and go to post # 25 and 22.

This diagram may help you to be sure your stuff is routed properly.

 

Thanks for the tips, but I think I've got ahead of you on the vacuum harness.
When I started fooling with this engine, it would not "idle" at less that 1100 rpm, then I found a big vacuum leak in the the brake booster, got the idle down to about 900 rpm. Yesterday I started looking at the vacuum harness, found that it was mis-routed in a couple of places, and patched in several places. I ripped the whole thing out, and beginning with the vacuum tee, "wired" the thing together with FLAPS vacuum hose, in accordance with the vacuum diagram on the decal under the hood. Now the engine idles, uninstallable, at about 600 rpm.

I'd not seen your CCV mod, or I'd have done it yesterday when I had the thing apart. I'll give it a couple of days to see what effect my amateur tampering had on it, then likely pull it down and do a directed. Thanks for the tip, BTW.

 

The orifice diameter will affect idle speed as will the intake manifold fitting. If they are dirty at all, the idle will be somewhat low.

Have you ever cleaned your throttle body and IAC?

 

Early on, I tested and eventually replaced the entire throttle body assy and attached sensors, I have confidence in the unit as it is now..

I had not checked the cleanliness/diameter of the small dia. orifice in the inlet manifold, will do so shortly. The end in the valve cover has been cleaned.

 

one thing to look out for is that many people replace vacuum hose with any hose they can find, and some of it doesn't have a thick enough wall to handle vacuum, and it collapses.

 

Yes my roomies 92 had the same ccv system and the po had used a vac line and it would collapse and cause a bad noise. Fixed it. ,my 88 woul dfill the air box in a week. I repalced the grommet it had no orifice it was melted to gether

 

PO's sometimes suck.