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i i-EMTSSTOru SUB SYSIEMS - Posf tive Crankcase {entilation System

During normal compression stroke, a small amount of gases in the combustion chamberesca[espastthepiston'Approximalely7O%ofthese''b1owby'.gaSeSareunburnedfuel(HC)that can dilute and contaminate the engine oil, cause corrosion to critical parts, and contribute ,tosludgebuiIdup.Athigherenginesp_eeds,blowbygaSeSincreasecrankcasepressurethatcan cause oil ieakage from sealed engine surfaces.

r Positive Crankcase Ventilation (PCV) system is to remove these harmful .gases from the crankcase before damage occurs and combine-them with the engine's normalincoming airlfuel charge. Fuel injected Toyota vehicles use two different types of closed PCVsystems to prevent the escape of crankcase vapors into the atmosphere:. Fixed Orifice PCV System i I i. PCV System Using Variable Flow PCV Valve

Fixed Orifice PCVSystem Air CleanerUsed on some early ToyotaEFlvehicles" Two fixedorifice valves were used tobalance the strength ofvacuum applied to ventilatelhe crankcase.

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EMISSION SUB SYSTEMS - iPositive Cran kcase Ve nti I ati o n Sysfem

PCV Valve

Used on all curent Toyotavehicles. A PCV valve isused to accuratety regulatebbwby flow back into theintake manifold.

PCV System Using Variable-Flow PCV Valve :Unlike fixed orifice iype systems, PCV systbms'that use a variable-flow PCV valve moreaccurately match ventilation flow with blowby production characteristics. By accurately matchingtheses two factors, crankcase ventilation performance is optimized, while engine performancePCV Valve FlowCharacteristics

As shouzn, the PCV valveflow characteristrbs close/y

m atc h blow by prod u ctioncharacteristbs.

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EMrSSrOn, SUB SYSIEMS - Posftive Crankcase Ventilation System

PCV System Components :Thevariable-flowtypePCVsystemsarealsoverysimpleindesi$nandponsistsofthefoliowing components". PCV Valve. PCV purge hose ,: :. Breather hose ;

PCV System OperationLike the previous system, this system also useis manifold vacuum to draw crankcase vaporsback into the intake manifold. Typically, blowby production is the greatest during high loadoperations and very light during idle and light load operations. Since thelcharacterigtics of Imanifold vacuum do not match the flow requirements needed for proper crankcase ventilation,a PCV valve is used to regulate blowby flow back into the intake manifold.. During idle and deceleration, blowby production is very low, but intake manifold vacuumis very high. This causes the pintle inside the PCV valve to-fully rqtract against springtension. The positioning of the pintle provides a small vacuum passage and allows forlow blowby flow to the combustion chamber.

PCV Valve(ldle, Deceleration)Pintle fully retracted ;

provides low blwrbyflowVacuum passage small

PCV valve open

. During low load qruising, the pintlerinside the PCV valve is positipned somewhat in thecenter of its travel. This positioning allows a moderate volume of blowby flow into the"combustion chamber. ;PCV Valve(Low Load Cruising)

Pintle centered ; providesmoderute blawby frow.Vacuum passage large

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PCV valve open

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EMTSSTOru SUB SySfEMS - Fositive Crankcase Ventitaticin System. During acceleration and high load operations, blowby production is very high. The pintleextends out further from the restriction allowing the maximum flow of blowby into the

combustion chamber. During extremely high engine loads, if blowby volume exceeds theability of the PCV valve to draw in the vapors, the excess blowby flows through thebreather hose to the air cleaner housing where it can enter the combustion chamber.

. When the engine is off or it backfires, spring tension closes the yalve compfetelypreventing the release of blowby into the intake manifold. The valve closes during abackfire to prevent the flame frorn traveling into the crankcase where it could ignite theenclosed fuel vapors. (PCV Valve(Engine Oll, Backfire)

Pintte futly ertended; valveclosed. ValveIPCV valve closed

PCV System Effects on Emissions and DriveabilityBecause PCV operation is factored into the proper operation of the feedpack control system,problems with the PCV system may disrupt the normal airi fuel ratio balance. A plugged PCVvalve will prevent the normal flow of crankcase vapors into the engine and can result in a richerthan normal airlfuel mixture. A plugged crankcase breather hose may cause the engine toconsume oil because of the increased level of crankcase vacuum. :ln addition, depending on the location of the fresh air breather hose, a nonfunctional valve orrestricted vacuum hose can cause oil contamination in the air cleaner housing or throttle borecoking. Always suspect and check the PCV system if you find traces of oil in the air intakesystem.

PCV Valve(Acceleration, llighLoad) Vacuum passage largePintle ertended ; providesmaximum blowby flow. PCV valve oppn

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I..EMTSSTON SUB SYSIEMS - Positive Crankcase Ventitation System

lfthecrankcasebecomesdilutedwithfuel,carbonmonoxide(Co)level$willlikelyincreasebecause the PCV system will meter extra fuel vapor into the intake system. Always replace fuel ,dilutedengineoilandidentifyandresoIvetheproblemcausingthefuelcontaminated.Although there are no mandatory maintenance intervals for the PCV system, periodica.lly check ithe system for a plugged or gummed PCV valve and damaged hoses. Replace suspect :components as necessary. Since PCV flow rates differ between vehicle.models, it is important 'to use the correct replacement PCV valve to ensure proper operation. The installation of an :incorrect valve may cause engine stalling, rough idle and other driveability complaints. Thus,never install universal type PCV valves!PCV System Functional TestsThe following RPM Drop Test may be used as a basic quick check to cohfirm that the PCV isystem is functioning:

.Starttheengineandallowittoreachoperatingtemperature' On TCCS equipped vehicles, connect TE to E1 at the diagnostic oonnector

:. Allow the engine to stabilize at idle' Pinch or block the hose between the pcV varve and vacuu, .ori."' Typically, engine rpm should drop around 50 rpm lf engine rpm does not change, checkthe PCV valve and system hoses for blockage. Replace componbnts as neceisary andthen retest the system. :

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