breathers in efi valve covers=vac leak?

[DirtKing]

I'm curious about this...of course it's a moot point for me now. Are you introducing un metered air into the engine??

[gtsr515]

Yes, open filtered breathers can cause driveability problems because they let in unmetered air, but this is not the same as a vacuum leak.

[NewAge 5.0]

what kinds of problems? popping? bucking? what do refer to as driveability problems....

[drudis]

IF you run a vacuum line from the throttle to the breather tube and you are drawing air thru another breather, then yes, you are sucking in unmetered air thru the other breather into the intake.

Without another breather. There is no crossflow (like sucking out a Coke bottle, its a vacuum). So no unmetered air.

If you plug the throttle vacuum line, and just run 2 breathers "venting" to atmosphere, not fed into the intake, then no (sort'a). You did meter the air coming into the intake, and the blowby (.1%) was metered and now going to atmosphere.
I did the second with my S-trim install.

[DirtKing]

alright...so if I had a breather in each valve cover, NO line to the throttle body and was running a pcv valve in the intake??? Under pcv conditions wouldn't the breathers vent IN not OUT??

[PKRWUD]

In theory.

However, once you get the rpms beyond idle, and the engine has a few miles on it, you'll end up with a nice, fine oil mist all over your engine compartment. This may take time to develo, but it will happen eventually.

Take care,
-Chris

[jimmyjamed]

your doing both. if your letting unmetered air in.... theres got to be a vacuum to suck it! if you take the oil cap off the valve cover, the rpm's will increase. put your hand over the hole and you'll feel the vacuum and the rpm's will go back down. lets say you disconnect the line from the pcv to the intake, wouldn't that be a vacuum leak? its still sucking ambient pressure, whether it goes thru the engine first or not. its less than ambient pressure where it taps off at the throttle body, which means less differential pressure, which equals less flow.

[PKRWUD]

Originally posted by jimmyjamed
your doing both. if your letting unmetered air in.... theres got to be a vacuum to suck it! if you take the oil cap off the valve cover, the rpm's will increase. put your hand over the hole and you'll feel the vacuum and the rpm's will go back down. lets say you disconnect the line from the pcv to the intake, wouldn't that be a vacuum leak? its still sucking ambient pressure, whether it goes thru the engine first or not. its less than ambient pressure where it taps off at the throttle body, which means less differential pressure, which equals less flow.

Yes, Grasshopper, but that of which you speak is crankcase vacuum, whereas the vacuum in question, is manifold vacuum. Manifold vacuum is the one that matters, because that is the air that reaches the combustion chamber. If a vacuum leak is developed regarding manifold vacuum, then unmetered air will enter the combustion chamber. Crankcase vacuum is caused primarily by a functioning PCV system, which in effect is really manifold vacuum. If you disconnect the PCV system, the crankcase vacuum should deminish.

To answer your question, if you were to disconnect the line from the PCV to the intake, it would only become a vacuum leak on the intake side. The hose going to the PCV valve would not be a vacuum leak. So, if you disconnected that hose, and plugged it at it's source (intake), then the other side of it (valve cover or rear of intake manifold, depending on application), would just be an unfiltered vent for the crankcase, not a vacuum leak.

Make sense?

Take care,
-Chris

[jimmyjamed]

but since manifold vacuum is the vacuum source for the crankcase vacuum, if you have extra air going into the crankcase, its gotta be going into the manifold. which is essentially a vacuum leak.
if you had a whole in your power brake booster, it would be the exact same thing, except air's leaking into the booster instead of the block.
it doesn't matter whats in between the vacuum source and the opening to ambient pressure, your still gonna have more flow in that line.

originally posted by PKRWUD
To answer your question, if you were to disconnect the line from the PCV to the intake, it would only become a vacuum leak on the intake side. The hose going to the PCV valve would not be a vacuum leak. So, if you disconnected that hose, and plugged it at it's source (intake), then the other side of it (valve cover or rear of intake manifold, depending on application), would just be an unfiltered vent for the crankcase, not a vacuum leak.

if you disconnect the line and plug it then yes, but were not talking about plugging the line line feeding the pvc valve, or isolating manifold vacuum. were talking about making an extra entrance for air to be sucked in thru, which will end up in the manifold, since manifold vacuum is the source.


pulling the oil cap and watching the idle increase is proof.

[MidNiteBlu 5.0]

I just put a breather cap to replace the oil filler cap about two weeks ago. I have had no problems whatsoever and it definently looks better.

[PKRWUD]

I had to read this three times to figure out what was being asked.

Originally posted by DirtKing
alright...so if I had a breather in each valve cover, NO line to the throttle body and was running a pcv valve in the intake??? Under pcv conditions wouldn't the breathers vent IN not OUT??

Let me explain it as simply as possible. Air, from outside the vehicle, is drawn in through the air filter and is then metered by the MAF while it continues it's path to the TB. When it gets there, it's got a choice. It either goes into the engine via the TB, or it enters the crankcase through the hose that goes to the oil filler tube. It goes through the engine and exits out through the PCV valve at the back of the engine. From there, it continues to it's new home, the intake manifold, where the vacuum is that has pulled it along it's journey. It proceeds to the combustion chamber, has a real hot time, and ends up in the exhaust pipes.

The reason this works is because the MAF metered it before it went on it's journey, knowing that it would eventually end up getting to the combustion chamber. If you were to make a change in this system by adding a breather, then the air would get into the engine, and eventually the combustion chamber, without having been metered by the MAF. The result would be a vacuum leak.

If you must have breathers, the only way to do it that won't create a vacuum leak is to plug both the port on the tb where the air headed for the fill tube, and the vacuum port on the manifold that the PCV hose goes to. If you skip either one of these, the result will be a vacuum leak.

Get it?

Take care,
-Chris

[jimmyjamed]

Thats what I've been saying lol

[Mach 1]

makes sense, but when I swap my breather for the oil cap, I see no change in idle surge or idle speed whatsoever. It still surges and idle speed doesnt change. Is this more noticeable on a stock engine?

[LX XLR8R]

but if you a SD motor then none of thise matters right?

[PKRWUD]

In an SD system, the PCV valve is supposed to regulate the flow, not allowing more than the ECM is programmed to expect, so using a breather would be fine. Just make sure to plug the hose going to the air cleaner. If you don't, you'll allow unfiltered air right into the engine.

Take care,
-Chris

[jruppert]

Anyone ever have to replace the screen mesh under the pcv? Mine seems to be plugged up. Plus, at higher rpms it wants to shove oil out the dipstick. I pulled the screen mesh out to clean but its too full of oil and crud. I am going tomorrow to buy a new screen at the ford dealership. I also notice oil puddling inside my Edelbrock upper intake. I understand that oil and fumes get pulled up there but should it puddle?

[Mach 1]

replacing your PCV screen should take care of the oil puddling problem

[jruppert]

Hopefully it takes care of the oil spitting out of the dipstick also.

[jruppert]

ok so i replaced the wire mesh screen behind the pcv valve and it still blows oil out the dipstick

[tireburner163]

too much crankcase pressure. But a breather on there or get a crankcase evacuation pump.