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PCV system testing
Topic Started: Nov 11 2014, 10:14 PM (603 Views)
Greywolf
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Mostly Harmless

When I thought about it, I realised that a lot of things can be caused by a malfing PCV system. At the same time, a lot of major trouble can be spotted by knowing what you are looking at with the PCV.

My normal method of checking them is determined by whether or not the PCV line runs to the air cleaner, or the intake manifold.

What it is:
The PCV system removes harmful gasses from the crankcase of an engine by using either air cleaner partial vacuum, or full vacuum from a port between the throttle plate and valves on the intake manifold itself.

Because the system uses intake air to pull gasses out of the engine and burn them in the cylinders, it can have an effect on intake vacuum if it is a manifold installed system, instead of a line run to the air cleaner.

The first test is to disconnect the PCV valve and if it is a manifold installed system cap the end of the line running to the intake. If the line or hose runs to the air cleaner, it doesn't need to be capped off.

Study the gasflow up out of the valve cover - since this is without a vacuum assist the gasses coming out can only be driven by blow by past the rings and pistons. This gas flow should be minimal.
This tests the mechanical condition of the rings and piston side clearances.

Step 1B: Put your thumb over the vent from the valve cover cap and see if it pushes your thumb away. If it does not, there could be a bad seal somewhere around the block, timing cover, or valve cover. THERE IS ALWAYS SOME PRESSURE from gas escaping past the rings and pistons, it is inevitable.

Step two:
You want to see if there are any gasket leaks around the engine, since with intake air pulling gasses out of the engine the flow can also pull oil vapor and droplets right out of the valve cover causing an excessive oil consumption problem and filth in the intake.
*Think of it like a vacuum cleaner with a 3/4 inch hose sucking the oil out of your valve cover...

You want that rate of flow to be very slow and gradual.

For an engine with the PCV line connected to the intake manifold itself, what you can do is connect a vacuum gauge to any convenient port, pull the PCV line and cap it, start the engine and read the vacuum gauge. Note the result.

Once you have done that, UN CAP the line to the intake manifold, and see if there is a drop in vacuum - if there isn't, you have air getting into the engine someplace that it isn't supposed to. What should happen is that there would be a drop in vacuum because the line is now pulling air straight in.

If that is true, it can pull oil right out of your valve cover and burn it in the cylinders at an unacceptable rate.

Under normal conditions there is a partial vacuum in the crankcase with a system like that at all times.

For air filter attached systems, I really don't know what to recommend for that. You can't really be expected to attach a clean line to the valve cover and try to blow back into the engine to see if there are any leaks when the engine is turned off, so step 1B above is about the best way to test for gasket and seal leaks.
Edited by Greywolf, Nov 11 2014, 10:51 PM.
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perfesser
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Elite Member - Former Metro owner

Gee, and all I've ever done is to take out the PCV valve and shake it to see if it rattled!! If it didn't, I'd run carb cleaner through it until it did, then put it back. You're actually using ... :O :O ... science!!

:thumb :thumb
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Mrbreeze


Ok, did I miss something or is PVC the hot topic right now?? Lol
Edited by Mrbreeze, Nov 11 2014, 10:44 PM.
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Greywolf
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I just couldn't help thinking about it some more, and you know - I guess a lot of people just don't understand it or what an improvement it is over the "OLD WAY"


I very often deal with machines that have been completely abused and trashed, so finding ways to determine what kind of shape it is in without a complete teardown can be a huge buck saver.
Edited by Greywolf, Nov 11 2014, 10:53 PM.
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Metromightymouse
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Powdercoat Wizard

Mrbreeze
Nov 11 2014, 10:42 PM
Ok, did I miss something or is PVC the hot topic right now?? Lol
Yes, I love talking about plastic pipe!! :whistle :D
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Greywolf
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Blonde lady at a parts store:
"My husband sent me to pick up a Polyvinylchloride Valve for his Metro..."

(Her husband was ALSO a blonde)


:whistle
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Rondawg
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Nice right up!
With this set up all ya would need to do is look to see if its working. Also a nice warm fuzzy feel good visual knowing there is a little less oil being burned. You could even save the oil collected and use it for chainsaw bar lube too!

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