Capping off your pcv system

[Wes]

Details:

302 stroked to a 347. Still EFI.
Vacuum hose connecting oil filler neck to throttle body on passenger valve cover, hose connecting under side of intake to rear pcv valve driver side valve cover, hose from rear pcv to front pcv on driver side cover. Hopefully you can visualize.
My plan, cap throttle body, oil filler neck, and under side of intake. Vent to atmosphere front and rear pcv valves on driver valve cover. I don’t feel like running a catch can at the moment. Maybe later. Anyone see an issue with this? It was vented sort of when I first got it. Front and rear pcv valves were not connected. No breather attached, just open. I connected everything properly and it could be my imagination, but it seems the idle has changed. While it was vented it had that high compression, hard hitting thump. Seems it slowed it to more of a lope. I could be talking out of my anus, but I wanted to check with people smarter than me.

Thanks homies!

 

[Croatan_Kid]

I'd probably just go straight for a catch can. It's designed to draw in some unmetered air if I'm not mistaken so it actually has some draw on the crankcase. I could be wrong though.

 

[Wes]

I'd probably just go straight for a catch can. It's designed to draw in some unmetered air if I'm not mistaken so it actually has some draw on the crankcase. I could be wrong though.

I’ve read that, but looking at the system I’m not sure how it would pull anything unmetered. Air is only coming in from the air intake at that point which hits the first sensor then on to the throttle body. Must be something to it though. I’ve read that on several forums.

 

[Tim C]

Personally I'd keep the PCV working. Oil lasts longer without getting dirty, condensation buildup will be less, less oil leaks and the engine will not wear out as fast. PCV was one of the first emissions systems, and engine longevity increased dramatically when it was introduced. PCV and evap canisters are two systems I usually try to keep as they are passive but they do their job (except OBD2 where the light comes on every 15 minutes because a loose cap, LOL)

The reason its idling slower and hitting harder capped off, especially if you didn't reset the keep alive memory (pull a bat cable or fuse) is because PCV is a metered vacuum leak. The computer is counting on that extra air bypassing the closed throttle to supplement the air from the IAC. When you capped it off, there was less air getting into the intake so it idles slower. Eventually the ECM will compensate by adjusting the IAC opening.

If you still want to do away with it, cap off the vacuum hose to the intake and the fresh air hose (from the tb to the oil filler) but run a breather filter, either the chrome kind or a miniature K&N on both valve covers. NO PCV Valves. Or ultimately a hose from each cover to a vented catch can. Either way you want BOTH valve covers to be vented.

If you want to keep the system, you only need one valve in one cover and a fresh air inlet on the other for the simplest setup. Factory would have been PCV in rear of cover without the oil fill (or into the lower intake where it pulls from the lifter valley depending on the car or truck) with hose to intake for vacuum. Then the fresh air inlet will be from the air filter (non vacuum side) of the throttle between it and the air filter (With MAF) to the oil filler cap stand pipe, or if no MAF it will sometimes go from the valve cover to a separate little filter inside the air filter box. The point is you want the fresh air going into the crankcase (that the PCV is using like a vacuum leak) to be drawn through the MAF so that air can be measured to add the appropriate amount of fuel to compensate. Two PCV valves T'd together is probably too much flow (vacuum leak) and that's not helping the idle either. If you need to plug the extra valve cover hole, just put a rubber cap over one of the PCV Valves and leave it in the valve cover to plug it.

Basically you want filtered air (and metered if you have a MAF) to flow into one cover, through the lifter valley and crankcase, and out the opposite valve cover through a single PCV for best results doesn't matter which goes where. There are other ways of doing it, like PCV in the lower intake to the valley, with fresh air inlets on both valve covers, but the first way is the simplest.

 

[Wes]

Personally I'd keep the PCV working. Oil lasts longer without getting dirty, condensation buildup will be less, less oil leaks and the engine will not wear out as fast. PCV was one of the first emissions systems, and engine longevity increased dramatically when it was introduced. PCV and evap canisters are two systems I usually try to keep as they are passive but they do their job (except OBD2 where the light comes on every 15 minutes because a loose cap, LOL)

The reason its idling slower and hitting harder capped off, especially if you didn't reset the keep alive memory (pull a bat cable or fuse) is because PCV is a metered vacuum leak. The computer is counting on that extra air bypassing the closed throttle to supplement the air from the IAC. When you capped it off, there was less air getting into the intake so it idles slower. Eventually the ECM will compensate by adjusting the IAC opening.

If you still want to do away with it, cap off the vacuum hose to the intake and the fresh air hose (from the tb to the oil filler) but run a breather filter, either the chrome kind or a miniature K&N on both valve covers. NO PCV Valves. Or ultimately a hose from each cover to a vented catch can. Either way you want BOTH valve covers to be vented.

If you want to keep the system, you only need one valve in one cover and a fresh air inlet on the other for the simplest setup. Factory would have been PCV in rear of cover without the oil fill (or into the lower intake where it pulls from the lifter valley depending on the car or truck) with hose to intake for vacuum. Then the fresh air inlet will be from the air filter (non vacuum side) of the throttle between it and the air filter (With MAF) to the oil filler cap stand pipe, or if no MAF it will sometimes go from the valve cover to a separate little filter inside the air filter box. The point is you want the fresh air going into the crankcase (that the PCV is using like a vacuum leak) to be drawn through the MAF so that air can be measured to add the appropriate amount of fuel to compensate. Two PCV valves T'd together is probably too much flow (vacuum leak) and that's not helping the idle either. If you need to plug the extra valve cover hole, just put a rubber cap over one of the PCV Valves and leave it in the valve cover to plug it.

Basically you want filtered air (and metered if you have a MAF) to flow into one cover, through the lifter valley and crankcase, and out the opposite valve cover through a single PCV for best results doesn't matter which goes where. There are other ways of doing it, like PCV in the lower intake to the valley, with fresh air inlets on both valve covers, but the first way is the simplest.

Hell of an explanation. Thanks man. It doesn’t have any way to vent on the passenger valve cover other than the oil filler neck. I ordered 2 vents, but they’re the type that clamp to the existing valve. So you’re saying don’t use those and go with the plug style? Thanks again

 

[Tim C]

Hell of an explanation. Thanks man. It doesn’t have any way to vent on the passenger valve cover other than the oil filler neck. I ordered 2 vents, but they’re the type that clamp to the existing valve. So you’re saying don’t use those and go with the plug style? Thanks again

If you're going to cap it, get a clamp on style breather that can go over the nipple on the filler neck, and replace the whole pcv valve with a breather on the other side. If intake clearance won't let you use a standard push in breather you can put an elbow into the grommet and clamp a breather onto that.

 

[Wes]

If you're going to cap it, get a clamp on style breather that can go over the nipple on the filler neck, and replace the whole pcv valve with a breather on the other side. If intake clearance won't let you use a standard push in breather you can put an elbow into the grommet and clamp a breather onto that.

Thanks man