PCV Blowing out of grommet

[Buckin'77]

Hello to all, I am a new (77) Bronco owner and am very excited about finally having one. I purchased one through the classifieds here and picked it up last Wednesday. I went out for my first ride yesterday and it was awesome even in it's current visual status. Somewhat diseased looking with the tan color and red and black primer spots but it still recieved numerous stares and looks from passerbys positive ones that is.

Okay enough happy talk I think I might have a problem. I drove the truck about forty miles, city and interstate, stopped for lunch and hit the interstate again and about two miles down the road I heard a pop and a pressure release that sounded like a semi realeasing air pressure. I looked behind me and did not see any oil or fluids on the road so I pulled over checked under the hood and the PCV was hanging out of the grommet. Puzzled I put it back in and proceeded and it happended three more times by the time I got home. I checked the valve and it seems to be free and I took the hose off of the carb base plate and the motor continued to run. I am not sure what is going on here the guy I bought the truck from said he did not rebuild the motor but he took the top end apart and oil pan off to inspect it it appeared to be in good shape and reassembled it with new gaskets and a Eldebrack intake and Carb.

Any ideas or opinions here? Thanks in advance, Rick

 

[70_Steve]

Pretty odd! Well, to state what seems like something obvious, it sounds like there's too much pressure building up in the crankcase. The PCV (Positive Crankcase Ventilation) system is supposed to pull gasses out of the crankcase and into the intake manifold to be burned. The "gasses" typically are blowby, and contain a lot of hydrocarbons. The PCV valve is supposed to regulate how much of the gasses get sucked into the intake manifold. In an engine with not much blowby (rings in good shape), there will be less gasses going into the crankcase from blowby than will be sucked into the intake manifold. So, on the opposite valve cover from the PCV valve, will be some source of clean fresh air. Some engines will have a tube coming from the top of the valve cover to the air cleaner. On my engine, for example, I just have a breather cap. My engine is in pretty good shape, and, at an idle, if I pull off the breather, so I just have the PCV hooked to the other valve cover, and put my hand over the breather hole for a little while, I can actually feel a vacuum being pulled.

So, things to check:
1. Make sure your PCV valve is clear and you can suck air through it. Same with the hose connecting it to the carb.
2. With the engine running, pull the PCV hose off the carb, and make sure you have a very strong vacuum. This is intake manifold vacuum.
3. Verify that on the opposite valve cover, you have some sort of fresh air supply. Either a hose from that valve cover to the air cleaner, or some sort of breather.
4. If you have something hooked to the opposite valve cover, make sure that it is not clogged.

 

[dan73]

If it keeps running with the hose pulled from the base of the carb sounds like the vacume port is clogged. Maybe the wrong gaskit. When you pull the hose does it change your idle speed at all?

 

[Buckin'77]

Remedy

I think I have it straightened out. The previous owner had put a oil filler cap with the PCV mounted in the cap and on the old PCV hole (left valve cover) he had blocked it off. I put the PCV back in the original place and got a regular oil filler breather cap. It has not blown out yet and when you pull the hose off the carb it starts to die.

Thanks for the help, Rick