Thread: ? about problem with pvc

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noticed a popping noise in the right exhuast pipe after the engine got warmed up, checked the plugs, timing, wires, etc. everything checked out alright. besides the poppings noise in the right exhuast, the engine runs great. on a chance, I removed the pvc that was on the right valve cover, installed a regular breather; & the popping stpped.
what would cause the pvc to make the engine make a popping noise in the exhuast on the same side the pvc is installed on?
the engine is a 1970 ls6 454 with cal custom valve covers that use twist-on style breathers. I was using the breather with a built in pvc in it. the pvc has no check valve, is basicly a tube welded to the breather. hose running from the breather went to a larger port on the back bottom edge on the holley carb.
any guess as to the problem with the pvc ?

A proper PCV chould have a check valve in it that prevents pulses from the intake from going into the valve cover. You need to have another open breather, usually on the another valve cover for the system to work right.

Pat

Originally Posted by Stu Cool

A proper PCV chould have a check valve in it that prevents pulses from the intake from going into the valve cover. You need to have another open breather, usually on the another valve cover for the system to work right.

Pat

the "pvc" breather that I used was a mr. gasket one, the only one I could find for the twist on type, the engine DID have a breather on the left side valve cover on the left side of the motor. the pvc was on the right valve cover.
so @ idle ,when the engine is warm the intake was sending pressure into the right bank thur the pvc since there was no check valve in it? causing the popping in the right exhuast pipe?

I don't see how a defective PVC valve would cause only one cylinder to "pop" regardless of which side it's on. Remove the PVC valve and cap the line that leads into the carb and start it up, my guess is that it will still pop.

I tried to find a simple diagram of a PCV system to look at but could not find a generic one. (Denny where are you?) The PCV moves air through the crankcase of your engine and needs an inlet and outlet. On a V8 the inlet is usually on one valve cover and can either be just a breather, or can have a pipe or hose that goes to the underside of the air cleaner. The outlet is usually on the other valve cover, and has the check valve in it. That goes to a vacuum source, usually at the manifold or to a plate between the carb and manifold. The check valve is needed in case the engine should back fire, it pushes the check valve closed and prevents any fire from going into the crankcase where it could ignite vapors inside the engine. The intent of the system is to pull fresh through the crankcase where it collects any unburned vapors and routes them back to the intake where they can be burned. It also takes care of any blow by and generally will keep the engine much cleaner. You can read much more detail here:

http://en.wikipedia.org/wiki/Positiv...se_Ventilation

It sounds to me like you have pieces mixed up where you have the connection from your breather going straight to vacuum and you do not have the other end of the system. Just remember it needs an inlet and an outlet to function properly.

Hope that helps you figure it out.

Pat

What I could find

I guess i didn't make the question clear enough!
1.)have a breather on the other valve cover (left side) & breather/pvc on the right valve cover which had a hose connect to the manifold vacum port on the botton rear side of holley carb.
2). when i started the car & while it is cold.. no problem, but when the engine gets up to temp (190)& or, been driven for 20 min. or more.. would have a popping noise coming out the right exhaust pipe when it is idling or in park with the engine running. ..checked everything... everything checked out o.k..., still had popping noise.
3). i then removed the pvc/breather & install a regular breather on the right vavle cover & capped the port on the carb..... so now there is a breather on both sides of engine....noise is gone !!!!!!!!!!!!!!!
4. so I know the problem is somehow linked or caused by the pvc valve(was not pluged up)???
5. ****I understand the basics of using a pvc valve and how to install it, & I would prefer to use one on this engine, BUT !!! I want to know why & how using the pvc valve is causing the poping noise in the right exhaust pipe when the car has been driven for awhile?????
6. this is not the first car i have built, & I have used a pvc valve sys. in all my cars, but this is the first time I have had a problem with a engine that is link to the pvc valve!!!!
does anyone have a answer to this problem, or have had it before on one of your own cars?????
thanks foir the help so far guys

try swapping the PCV and breather sides. Would be intresting indeed if the popping follows the PCV.

I eliminated PVC valves on both my engines and intend to do the same on the third. Sorry, I wish I had and answer for you.

Originally Posted by firebird77clone

try swapping the PCV and breather sides. Would be intresting indeed if the popping follows the PCV.

will do that tommorrow, will post result

I don't understand why the PCV has no check valve?

as I said ,it is a old style twist on breather, the hole way to large for a grommet & a regular push in pvc. used on newer style valve covers.
the valve covers are cal-custom finned covers, mid-60's.
the breathers fit into the valve cover hole & twist on & lock on the valve covers, the same way a radiator cap locks onto the radiator.
I don't think there is a issue of any kind of pressure going from the manifold to the valve cover,(engine is not backfireing thur the carb). it only make the popping noise, when the engine is up to running temp, been driven, & is then idleing, like stoped at a light.
I am going to re install the breather/pvc on the other side of the engine to see if it starts popping on the left side, will post

I'll be interested to know what you find out after the switch. They make inline PCV valves that you can put in the hose. They are cheap, would be worth a try if the noise follows the move. If the popping is caused by a lean condition, that could be happening because of an unrestricted vacuum "leak" when at idle as that is a high vacuum condition. At higher speeds, more air would be flowing through the throttle body and bringing fuel with it so the lean condition would be reduced. Not sure why it would just show up on one side though if the port opens into the plenum.

Pat

i did the switch with the pvc / breather, did the same thing when the engine get warm, so it has it be something with this generic stlye breather/ pvc. does anyone have the part # for a inline pvc valve, hopefully using a modern ture pcv valve will work fine, just have to find a inline one.

Sounds like thats not a PCV,especially if it doesn't have a check valve and it is running full manifold vacume to the breather,driving that side of the carb way lean.