300 I6 Running Funny. Help?
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300 I6 Running Funny. Help?
I have an '83 F-150 with the 300 inline in it and just recently it started making a strong vacume noise and we played around with it until we removed the oil cap on the valve cover and it is sucking air pretty strong through there? Any idea what is wrong or how to cure it? Thanks!
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That is the desired behavior; the PCV valve allows the engine to suck out blowby gasses and injects them back into the combustion chambers. Some oil fill caps double as air filters to provide filtered air to replace the volume removed via the PCV valve.
Investigate your power brake booster (if equipped) as that can make the type of noise you're describing when it fails.
Investigate your power brake booster (if equipped) as that can make the type of noise you're describing when it fails.
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Ok. I don't believe it has a power break booster. But this has never happened before. I've done alot of work to this truck and engine and it never sucked like this, it also is missing and I don't know if the strong suction is a relation.
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It may be that the Positive Crankcase Ventilation (PCV) valve has failed such that full vacuum is going to the crankcase. The PCV valve is supposed to restrict the amount of vacuum, but I suppose it could fail to do that.
The PCV valve is stuck into the valve cover and connected to the base of the carb or intake manifold via a rubber hose. Pull the valve out and shake it - it should rattle. In fact, you should hear it rattle when the engine is running. I would replace it were it me since they are very inexpensive and should be replaced often anyway.
The PCV valve is stuck into the valve cover and connected to the base of the carb or intake manifold via a rubber hose. Pull the valve out and shake it - it should rattle. In fact, you should hear it rattle when the engine is running. I would replace it were it me since they are very inexpensive and should be replaced often anyway.
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It shouldn't whistle. Something's wrong as it is pulling too much air, and the only thing that meters the air is the PCV valve. Don't see how it could be anything else, but I have been known to be wrong. In fact, AFAIK, I haven't been wrong yet today so I'm due. 
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Oh, btw, if it is pulling as much air in as it sounds like the engine isn't going to be happy at idle. That's because you have way too much air going in than was expected. Or, to put it another way, you have more air going in than was going in when the idle mix was adjusted. So, the air/fuel ratio is way lean and the engine isn't going to idle well and may even miss at lower RPM.
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lets hope that's what it is...one of the alternatives is not good. I saw on one engine, with a screw in rocker stud, where the head cracked right at that boss were the stud screws in on an intake valve.
It was sucking in through that crack, also was sucking oil in. Your engine is not all of a sudden smoking is it?
I think this would be extremely rare, PCV is much, much more likely
It was sucking in through that crack, also was sucking oil in. Your engine is not all of a sudden smoking is it?
I think this would be extremely rare, PCV is much, much more likely
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Perish the thought! Ouch, that would be bad. And, it does fit all the symptoms, although it does add one - smoke. I have money on the PCV valve, but not enough money to rebuild a head.
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It's not smoking and it has been like this for 2 days now so along with you guys I am hoping it is the PCV valve. Either way the engines getting pulled this summer and rebuilt just cause my dad loves that truck and loves how that engine pulls and will never want to get rid of it.
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Ok so I pulled the PCV valve and it all stopped so I am going to pick another one up this evening! Thanks everyone for the info, on the bright side my father picked up a strong running 300 last night for $50 so I'll have a replacement if the head would crack. Thanks Again
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