Ls1 PCV help needed
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Teching In
Joined: Jun 2021
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From: Maryland
Ls1 PCV help needed I am wrapping up a heads and cam build I did on my 99 camaro and need help understanding the pcv routing. Previously before the heads and cam swap there was a breather on the rear driver side valve cover and a pcv line going from my passenger valve cover to my manifold behind the throttle body. Am I able to just run a line between the 2 ports on my valve covers and t it off with a line going to the manifold behind the throttle body? I appreciate the help thank you.
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PCV requires a PCV valve or orifice (duh) that has manifold vacuum applied to it, to draw vapors and whatnot out of the crankcase. Usually that's on the driver's side valve cover.
It also requires "makeup" air, fresh clean filtered air let into the crankcase, to replace the dirty air removed by the PCV valve.
A car with a MAF requires that the makeup air be sourced from behind the MAF butt in front of the throttles. Otherwise the PCV will draw in air that hasn't gone through the MAF; the ECM won't know it's there, since the MAF is the ECM's "eyes" on airflow into the engine; and it won't know that it's supposed to put in any fuel for it; therefore it'll run STUUUUUPID lean at idle especially. This can somewhat sometimes sorta kinda be compensated for in the tune if idle isn't real important and can be just kinda half-assed enough that it'll "run", like a PURE RACE ONLY application, but it's never going to really be "right" that way, and will majorly struggle on the street.
A "breather" ANYWHERE in the system lets air in that bypasses the MAF. Such a system almost always causes trouble, particularly with idle. At idle the amount of air coming into the engine is very small (duh), thereby making the air-metering error introduced by a majority of the incoming air coming from the PCV system butt bypassing the MAF, the most serious.
So, no, if you want your car to run right, you can't do what you're proposing.
Run it in the stock configuration. PCV valve/orifice to manifold vacuum, other VC's port to a source of filtered air behind the MAF. No "breather" anywhere. If you need a catch can, install that in the line between the PCV valve/orifice and the manifold vacuum source, and make sure it seals up well (no vacuum leaks).
It also requires "makeup" air, fresh clean filtered air let into the crankcase, to replace the dirty air removed by the PCV valve.
A car with a MAF requires that the makeup air be sourced from behind the MAF butt in front of the throttles. Otherwise the PCV will draw in air that hasn't gone through the MAF; the ECM won't know it's there, since the MAF is the ECM's "eyes" on airflow into the engine; and it won't know that it's supposed to put in any fuel for it; therefore it'll run STUUUUUPID lean at idle especially. This can somewhat sometimes sorta kinda be compensated for in the tune if idle isn't real important and can be just kinda half-assed enough that it'll "run", like a PURE RACE ONLY application, but it's never going to really be "right" that way, and will majorly struggle on the street.
A "breather" ANYWHERE in the system lets air in that bypasses the MAF. Such a system almost always causes trouble, particularly with idle. At idle the amount of air coming into the engine is very small (duh), thereby making the air-metering error introduced by a majority of the incoming air coming from the PCV system butt bypassing the MAF, the most serious.
So, no, if you want your car to run right, you can't do what you're proposing.
Run it in the stock configuration. PCV valve/orifice to manifold vacuum, other VC's port to a source of filtered air behind the MAF. No "breather" anywhere. If you need a catch can, install that in the line between the PCV valve/orifice and the manifold vacuum source, and make sure it seals up well (no vacuum leaks).
Last edited by RB04Av; Apr 12, 2024 at 07:17 PM.
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From: Central Cal.
Ideally you need a clean air source AFTER the MAF but before the butterfly, routed to one valve cover.
From the other valve cover run a line to a manifold vacuum source after the butterfly.
This 2nd valve cover should have a small orifice, OR there should be a PCV valve in the line to the manifold vacuum source.
From the other valve cover run a line to a manifold vacuum source after the butterfly.
This 2nd valve cover should have a small orifice, OR there should be a PCV valve in the line to the manifold vacuum source.
