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PCV valve system 90 f150 4.9L

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Old 03-27-2012, 05:23 PM   #1
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Default PCV valve system 90 f150 4.9L

Im wanting to know how the valve works exactly. Its hose goes into the air cleaner housing. To check the valve i shook it and heard nothing. When i turn on the car, is there supposed to be a vacuum that goes towards the filter housing or towards the engine? Thanks
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Old 03-27-2012, 07:24 PM   #2
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Most valves should rattle a bit when you shake them, indicating the plunger is free.

The PCV system is one of the earliest/first emissions control features offered. It works by drawing combustion blow-by and vapors in the crankcase back into the intake for combustion rather than freely releasing into the atmosphere. An additional feature is that it helps keep the oil cleaner longer.

The valve is lightly spring-loaded so as to be shut with the engine off or at very low vacuum levels such as WOT take-offs. Sufficient engine vacuum will pull the valve open and draw blow-by from the crankcase into the intake. This air removed must be replaced somehow, or else the crankcase would approach the vacuum level of the intake.

In our case, this replacement air is drawn in through the tube you mentioned, being filtered in the air filter enclosure. Some vehicles use something as simple as a screened mesh on the oil filler cap or parasite a filtered feed after the main air filter.

Some notice that the PCV air filter will become oily. Suggest this is due to a downward slope of the tube, allowing condensing vapors to run toward the filter, or perhaps excessive cylinder blowby overcoming the capacity of the PCV system.

At any rate, suggest to either clean or change your PCV valve, inspect / change the filter as needed, and you should be good-to-go.
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Old 03-27-2012, 07:59 PM   #3
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It essentially regulates the amount of air and blow-by gases to the intake manifold and prevents any backfire to go into the crankcase.
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Old 03-27-2012, 08:57 PM   #4
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If it's not rattling when you shake it, replace it. If you can, go with a Motorcraft PCV over the others. There is a difference.
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Old 03-27-2012, 11:25 PM   #5
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I can' speak for the 90 model, but the 95 has a breather tube for crankcase intake that runs into the air box. The pcv valve is on the rear of the valve cover with it's own hose running into the intake itself. It's the crankcase intake on the front and crankcase exhaust out the pcv valve on the rear. The pcv valve is located under the egr tube on the rear of the valve cover.

Last edited by unit505; 03-27-2012 at 11:31 PM.
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Old 03-28-2012, 03:53 AM   #6
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Thanks all i think i got it
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