318 Auto Engine Repair Copyright by Goodheart-Willcox Co., Inc. Blowby fumes Fresh air Fresh air Blowby liquid-vapor separator PCV valve controls flow to manifold Plunger Intake manifold Fumes sucked back into combustion chambers Figure 15-18. The positive crankcase ventilation system uses engine vacuum to draw toxic crankcase fumes into the intake manifold. These fumes are then burned in the combustion chambers. The PCV valve controls flow so the mixture at idle is not too lean. (Honda) Engine Not Running or Backfire To intake manifold To valve cover PCV valve is closed Normal Operation PCV valve is open, vacuum passage is large Idling or Decelerating PCV valve is open, vacuum passage is small Acceleration or High Load PCV valve fully open Figure 15-19. Study the operation of a PCV valve in different modes. (Toyota) 1 2 3 5 7 4a 8 9 10 11 6 1 2 3 5 7 4b 8 9 10 11 6 1 2 3 5 7 4c 8 9 10 11 6 Hot Air Position for Warmup Temperature Control or Blend Cool Air Position 1 Vacuum diaphragm motor 2 Diaphragm spring 3 Temperature sensor 4a Air bleed valve—closed 4b Air bleed valve—partially open 4c Air bleed valve—open 5 Vacuum hoses 6 Diaphragm 7 Heat stove 8 Hot air (exhaust manifold) 9 Damper door 10 Outside inlet air 11 Snorkel Figure 15-20. A thermostatic air cleaner maintains a rela- tively constant air inlet temperature to improve combustion. (General Motors) fuel injection system can be calibrated leaner to reduce emissions. Evaporative Emissions Control System The evaporative emissions control (EVAP) system prevents vapors in the fuel system from entering the atmo- sphere, Figure 15-21. A fuel tank vent line carries vapors from the fuel tank to a charcoal canister in the engine com- partment. The charcoal canister stores fuel vapors when the engine is not running. The metal or plastic canister is filled with activated charcoal granules. The charcoal is capable of absorbing fuel vapors. The top of the canister has fittings for the fuel tank vent line and the purge (cleaning) line. The bottom of the canister has an air filter that cleans the out- side air as it enters the canister. A liquid-vapor separator is frequently used to keep liquid fuel from entering the EVAP system. It is simply a metal tank located above the main fuel tank. Fuel vapor