How do you actually check a PCV valve?

[wrogers55]

I have a 418 SBF with a PCV setup on the passenger bank, piped into vacuum port of a MassFlow FI. Driver side has a typical small air filter canister. This is a big HP motor that is street driven only.

The PCV valve plugs into the valve cover and the hose runs off of it at a 90. Two things:

1. The valve seems to have no restriction, blowing through it either way. Problem or no?

2. Big oil consumption problem, maybe 1-2 quarts in 500 miles, but no sign of where it's going for that kind of use.

I'm wondering if a lot of oil vapor or droplets are being sucked out of the valve cover area into the intake. That little PCV valve sits right over a rocker on the Ford Racing cast covers, and I mean it's close!

Any ideas?

[Rick Parker]

It should be shielded from splash to prevent sucking droplets and ultimately volumes of oil.

[patrickt]

Unbaffled valve covers on PCV systems can result in gobs of oil getting sucked up. The easiest way to tell is to just plug off your PCV, adjust your carbs so the engine runs nicely, and then check your oil consumption after 500 miles. PCV is a good thing though, so don't get rid of it just because of oil consumption. The classic method of testing your valve is to pinch your hose or put your finger over the end of the valve. Remember though, a PCV is a "controlled manifold leak" and that particular valve might fit, but not be exactly right for your engine. But if your only complaint is the oil consumption, then putting a baffle in your cover is the answer. Here's a nice little write up on what a PCV valve does to get you up to speed: http://mgaguru.com/mgtech/engine/cv103.htm

[Tony Radford]

Wayne, I was facing the same issue. How do you really tell what's getting sucked into the manifold. I purchased an in-line water filter intended for a compressor at Lowe's. It has a glass bowl and sits in line with my PCV line to the intake manifold. Even though my valve covers are baffled, the bowl eventually fills up with oil. Takes a while, but it does fill up.

[mr0077]

Shake the PCV valve...if it rattles, it is probably working correctly. In operation, the PCV valve gets sucked (almost) shut under high vacuum, and opens up when the vacuum drops off, so just sucking or blowing on it won't test it. With the engine running, put your finger on the engine side of the PCV valve and you should feel engine vacuum, and the valve should rattle, but take your finger off (at idle) and the valve quits rattling 'cause it gets sucked shut.

The above recommendations are right, you need a baffle below the PCV valve hole in the valve cover. Check the hose to the EFI for oily residue...a normal PCV hose on a normal engine will have a slight oil residue but should not be "very" oily.

[olddog]

I too have a Mass Flow EFI. If you are sucking down a quart or so of oil in 500 miles and your cam has a fair amount of overlap, there is a good chance that your mass flow meter will get oil on the wires. If so, it will through the meter off quite a bit.

If you can see the rocker arm with the PCV pulled, your missing the baffle. Then the next question, is there enough rocker clearance to put the baffle in? If not, you will need taller valve covers or will need to modify the intake to mount the PCV there.

[Double Venom]

Gentlemen,
Correct me if I'm wrong...(I'm sure someone will!) But blowing into one end of the PCV valve should -NOT- let air through, while blowing through the other end should allow air to flow freely!

It should not allow Air/Oil to flow both ways! ?
Dv

[Tony Radford]

The pressure is higher in the case than in the intake path, so some of the block pressure is bled off by porting it into the intake (in my case). If it were just a pipe (no valve), the fuel/air mixture in the intake would be able to backflow into the block through the head if the pressure differential were shifted back (not sure how that would happen). Regardless, the PCV is a valve. By the way, I was never able to tell that the oil was flowing into the intake before installing the separator. I tried installing an inline fuel filter in hopes it would catch some oil residue, but it never did. The oil is atomized in the air so well that only a proper filter system will trap it out.

[trularin]

Ed is right, there is a spring that only allows the vapors to be pulled from the crank case. The spring slams the valve shut to should something present a pressure Greater that crank case pressure.

It is how the valve works.



Test: start engine and allow to idle. PUll PCV valve and note change in engine RPM not to exceed 200 - 500 RPM. Place finger over end of valve and feel valve shut. Vacuum draw on finger should be no greater that 12 - 20 inches of mercury and steady ( this is vacuum seepage ). Release valve and note the valve should sham open and vacuum should be the same as manifold vacuum.
Clean with approved O2 sensor carb cleaner.

Just my $0.02 worth.

[mr0077]

The PCV is normally open when the engine is off due to a weak internal spring and gravity. When you start the engine, manifold vacuum pulls the shuttle valve inside the valve housing closed, and allows a slight metered amount of air into the intake. When manifold vacuum drops (such as when opening the throttle under load), the internal spring pushes the shuttle open to allow a greater flow (hopefully of any blowby plus fresh replacement air from the other valve cover) thereby allowing the crankcase to be ventilated. So, at idle the PCV is essentially closed, and passes very little air; it only passes a significant amount of air and vapors when the engine is off idle and under load.

When you pull the valve out of the valve cover (or wherever) while it is hooked to an idling motor, the manifold vacuum has the internal shuttle pulled into the "closed" position, and it will not rattle. Put your finger on the bottom of the valve housing and you cause the vacuum to be the same on both sides of the shuttle (equal to manifold vacuum), so the spring pushes the shuttle into the open position, allowing it to rattle when shaken (that's the "shade-tree" method to test it). When you take your finger off the bottom of the valve, air flows toward the manifold, the engine vacuum pulls it shut against the weak spring pressure, and it won't rattle. All this assumes a properly functioning PCV valve.

[SuperHart]

In case anyone needs a hint about how to construct and install oil baffles please go to my Cobra Build Page #5 http://home.comcast.net/~superhart/cobra5.htm and scroll about halfway down the page for a baffle discussion. These home made baffles have worked well for me.

[zrayr]

Originally Posted by Tony Radford

Wayne, I was facing the same issue. How do you really tell what's getting sucked into the manifold. I purchased an in-line water filter intended for a compressor at Lowe's. It has a glass bowl and sits in line with my PCV line to the intake manifold. Even though my valve covers are baffled, the bowl eventually fills up with oil. Takes a while, but it does fill up.

I use one of these. It works.:

http://www.conceptualpolymer.com/new_page_1.htm





Z.

[wrogers55]

I started this post, but here is another twist.

I just discovered that the motor has a a grommet on the filter side valve cover that has a built in baffle (molded rubber) that shields the opening into the valve cover. The PCV side (passenger valve cover) grommet is just a donut rubber ring with the hole clear to the rockers that must allow this thing to really suck oil vapors and droplets out of the cover like crazy.

That has to be backward as far a the grommets go.

Doesn't really seem like a very good baffle anyway.

[mr0077]

Either switch the valve covers or (maybe easier) swap the PCV valve and the breather locations?

Oops, I just re-read your post and I guess a swap wouldn't work, unless the PCV valve will fit into the breather grommet...

[wrogers55]

Yep, the grommet internal hole sizes are identical, so I'm swapping them side for side. I'm not at all sure that will fix the oil consumption problem, but it can't hurt.