Toyota Pick-ups/Land Cruiser/4Runner 1989-1996

Crankcase Ventilation System



See Figures 1 through 5

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.

The recirculation system relies on the integrity of the engine seals. Any air leak around the valve cover, head gasket, oil pan, dipstick, oil filler cap, air intake ducts, vacuum or breather hoses can introduce excess air into the fuel/air mixture, causing rough running or reduced efficiency. Likewise, a plugged hose or passage can cause sludging, stalling and oil leaks.


Inspect the PCV system hoses and connections at each tune-up and replace any deteriorated hoses. Check the PCV valve at every tune-up and replace it at 30,000 mile (48,000 km) intervals.

The PCV valve is easily checked with the engine running at normal idle speed (warmed up).

  1. Remove the PCV valve from the valve cover or intake manifold, but leave it connected to its hose.
  3. Start the engine.
  5. Place your thumb over the end of the valve to check for vacuum. If there is no vacuum, check for plugged hoses or ports. If these are open, the valve is faulty.
  7. With the engine OFF , remove the valve completely. Shake it end-to-end, listening for the rattle of the needle inside the valve. If no rattle is heard, the needle is jammed (probably due to oil sludge) and the valve should be replaced.

Don't blow directly into the valve; petroleum deposits within the valve can be harmful.

An engine without crankcase ventilation is quickly damaged. It is important to check the PCV at regular intervals. When replacing a PCV valve you must use the correct one for the engine. Many valves look alike on the outside, but have different mechanical values. Putting the incorrect valve on a vehicle can cause a great deal of driveability problems. The engine computer assumes the valve is the correct one and may over adjust the ignition timing or fuel mixture.

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Fig. Fig. 1: The PCV valve functions differently according to engine operating conditions

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