Purpose of Lifter Cvr Ventilation Hose vs PCV Valve

[VIBE CAM]

Greetings All....what is the purpose and function of the lifter cover ventilatioin hose that connects to the air intake snorkel just before the throttle body ? And doesn't it make the PCV valve unnecessary ? Please teach me what / why this hose is there and the directionof air flow thru it at start up, running, etc. Thanks

[455SD]

Your Vibe has a PCV valve. The hose coming from the Head Cover to Air Filter Box is part of the PCV system. As your PCV opens, allowing intake vaccum to pull vapors from the crank case, fresh air is circulated back into the crank case through the HC. This basically allows the engine to purge the small amount of blow-by from between the ring to cylinder wall, from the combustion chamber, and reburn it. Vacuum(negative pressure) out past open PCV, backfilled by fresh air. ZZ has PCV in the HC, ZR has PCV mounted into the side cover of the Cylinder Block.
Hopefully, this expanation hasn't caused more confusion

[VIBE CAM]

Thanks for reply 455SD. Your explanation helps settle an argument between me and myself and two theories, especially since I do not have the equipment to measure vacuums or pressure zones at various places in the cold air intake snorkel, lifter cover, etc. I should have put in the original question that I'm looking at a 2008 Vibe w electric throttle + engine coolant heater lines for throttle defrosting. My original analysis thots are as follows. If positive pressure, from the ring blow-by, exists in the lifter cover (and hence the usual need for a PCV valve) wouldn't that pressure take the path of least resistance(since the PCV is spring loaded) and use the ventilation tube to vent into a lower pressure zone of the fresh air intake snorkel. I say relatively lower pressure in the snorkel because of the butterfly being open and intake manifold sucking air. Your answer would tell me that they are using an air circulation system and there is positive air pressure in the snorkel at the point of connection and blowing in fresh clean air to the lifter cover. Still not sure why they use a spring loaded PCV if the car is not moving and not forcinng air into the lifter cover. I notice on earlier model years w a cable throttle control that the vent tube appears to connect directly to or between the throttle body and toward the intake manifold and hence even more likely a vacuum on the vent hose. Makes me even more curious what the air pressure profiles are of that hose line setup. Couldn't get any mechanics at Toyota to talk to me last week as they were behind in their repair schedules and working on commission for repairs.

[455SD]

Still not sure why they use a spring loaded PCV if the car is not moving and not forcinng air into the lifter cover. I notice on earlier model years w a cable throttle control that the vent tube appears to connect directly to or between the throttle body and toward the intake manifold and hence even more likely a vacuum on the vent hose. Makes me even more curious what the air pressure profiles are of that hose line setup.

When the engine is shut off, spring pressure closes the C/Case via PCV valve, to keep unburned hydrocarbons from exiting back out of the filter box. At idle, or decel, when vaccum in Intake Manifold is highest, the valve is slightly unseated, to let the small amount of blow-by to be recirculated. When the engine is accellerating, vaccum drops, and allows the valve to be opened further, by the spring, allowing more volume of circulation without dramatically changing the air/fuel mixture. I don't think that there is a whole lot of difference in why the vent hose is closer to the throttle body on some vehicle applications, other than maybe cooler air, which would help condense any oil vapors out of the combustible hydrocarbon mix. This would help keep from "using" oil as this mix gets pulled back into the Intake. Suspended oil vapor gets cooled in the Head Cover, and forms droplets, which are then caught in the baffle system built into the H/C, allowing oil to drain back to pan.

Glad to help out

[VIBE CAM]

Thanks again 455SD for your insights. I will be moving on to other projects now.