See Figures 1, 2, 3, 4, 5, 6 and 7
A closed, positive crankcase ventilation system is employed on all Toyota trucks. This system cycles incompletely burned fuel which works its way past the piston rings back into the intake manifold for reburning with the air/fuel mixture. The oil filler cap is sealed and the air is drawn from the top of the crankcase into the intake manifold through a valve with a variable orifice.
This valve (commonly known as the PCV valve) regulates the flow of air into the manifold according to the amount of manifold vacuum. When the throttle plates are open fairly wide, the valve opens to maximize the flow. However, at idle speed, when manifold vacuum is at a maximum, the PCV valve throttles the flow in order not to unnecessarily affect the small volume of mixture passing into the engine.
During most driving conditions, manifold vacuum is high and all of the vapor from the crankcase, plus a small amount of excess air, is drawn into the manifold via the PCV valve. However, at full throttle, the increase in the volume of blow-by and the decrease in manifold vacuum make the flow via the PCV valve inadequate. Under these conditions, excess vapors are drawn into the air cleaner and pass into the engine.
See Figure 8
Check the PCV system hoses and connections, to ensure that there are no leaks; then replace or tighten, as necessary.
To check the valve, remove it and blow through both of its ends. When blowing form the side which goes toward the intake manifold, very little air should pass through it. When blowing from the crankcase (valve cover) side, air should pass through freely.
Replace the valve with a new one, if the valve fails to function as outlined.
Do not attempt to clean or adjust the valve; replace it with a new one.
REMOVAL & INSTALLATION
- Remove the PCV valve from the cylinder head cover on all engines. Remove the hose from the valve.
- Remove the valve from the manifold-to-crankcase hose.
- Check the valve for proper operation and then insert it into the manifold-to-crankcase line.
- Insert the other end of the PCV valve into the cylinder head cover.