Scion 90999-92002 Hose, Vacuum

The Positive Crankcase Ventilation (PCV) system reduces hydrocarbon emissions by scavenging crankcase vapors, circulating fresh air from the air cleaner through the crankcase to mix with blow-by gases before being drawn through a PCV valve into the intake manifold. It consists of the PCV valve and two hoses: one connecting the air filter housing to the crankcase and the other, containing the PCV valve, connecting the crankcase to the intake manifold. To maintain idle quality, the PCV valve restricts flow when intake manifold vacuum is high, but under abnormal conditions, it allows excessive blow-by gases to flow back into the air cleaner for combustion. Although there is no scheduled inspection interval for the PCV valve or hoses, efficiency may decline over time due to sludge buildup, leading to symptoms like leaking seals from pressure buildup. Regular inspection and cleaning of the hoses during oil changes or other maintenance tasks are advisable, and any cracked or deteriorated hoses should be replaced. For component replacement, the fresh air inlet hose can be removed by sliding back the spring-type clamps and disconnecting it from both the air filter housing and the right valve cover pipe. The crankcase ventilation hose is similarly removed by disconnecting it from the PCV valve and intake manifold. The PCV valve itself is accessed after removing the crankcase ventilation hose and can be unscrewed from the left valve cover. Hoses should be inspected for clogs or dirt, cleaned if necessary, and replaced if damaged. The PCV valve should also be checked for clogs, cleaned with solvent, and replaced if residue cannot be removed. Installation follows the reverse order of removal.

To reduce hydrocarbon (HC) emissions, the Positive Crankcase Ventilation (PCV) system is used to route crankcase blow-by gas to the intake manifold for combustion in the cylinders. This process involves mixing the blow-by gases with incoming fresh air before burning them in the combustion chambers. It is vital to check the PCV hose for any damage and replace it as soon as possible. It is also crucial to inspect the hoses, connections, and gaskets that affect the PCV system, and tighten, repair, or replace any of these.

The Positive Crankcase Ventilation (PCV) system reduces hydrocarbon emissions by scavenging crankcase vapors, circulating fresh air from the air cleaner through the crankcase, where it mixes with blow-by gases before being rerouted through a PCV valve to the intake manifold. Utilizing intake manifold vacuum, the system draws crankcase vapors into the intake manifold, with the PCV valve regulating the amount of blow-by gases returned based on available vacuum, while also preventing combustion gases from entering the manifold during a backfire. To maintain idle quality, the valve restricts flow when vacuum is high. The system includes a fresh-air inlet hose connecting the air intake duct to the crankcase, the PCV valve, and the PCV hose linking the valve to the intake manifold, with the valve attached to a crankcase vent oil separator that prevents oil from entering the valve. Regular inspection of the fresh-air inlet hose and the PCV valve hose for cracks, leaks, and damage is essential, along with checking for obstructions by disconnecting the hose from the crankcase vent oil separator and the intake manifold; clogged hoses should be replaced, and if the PCV valve is not functioning properly, it should also be replaced rather than cleaned.

To check the PVC valve, first attach a clean section of hose to the cylinder head side of the valve and blow through it. Air should pass through easily. Then, blow through the intake manifold side of the valve and verify that air passes through it.

To remove, detach the hose, unscrew the valve from the cover, then reattach the hose to the valve.

Fresh air enters the crankcase, mixes with blow-by gases, and exits through the PCV valve into the intake manifold. At high vacuum (idle/cruise), flow is steady; under load, flow increases to reduce pressure and emissions.

When purchasing a replacement valve, make sure it's for your particular vehicle and engine size. Also, compare the old valve with the new one to ensure they're the same.

Attach a clean section of hose to the cylinder head side of the valve and blow through it. Then blow through the intake manifold side of the valve and verify that air passes through with difficulty.

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