TM 10-3930-653-14&P The function of this system depends upon the positive crankcase ventilation (P.C.V.) control valve which returns blow-by gases to the combustion chamber. Normally,   the   capacity   of   the   valve   is   sufficient   to handle any blow-by gas and a small amount of ventilating air. The  ventilating  air  is  then  drawn  from  the  carburetor air  cleaner,  through  the  tube  connecting  carburetor  air cleaner to the rocker cover, into the crankcase. Under  full-throttle  condition,  the  manifold  vacuum  is insufficient  to  draw  the  blow-by  flow  through  the  valve, and   its   flow   goes   through   the   tube   connection   in   the reverse direction. On  lift  trucks  with  an  excessively  high  blowby,  some of’  the  flow  will.    go  through  the  tube  connection  to  the carburetor air cleaner under all conditions. Fig.  4-14.  Crankcase Emission Control System (2) INSPECTION (1) P.C.V.  valve Check P.C.V.  valve in accordance with the following method. With   engine   running   at   idle,   remove   the   ventilator hose  from  the  P.C.V.    valve,  if  the  valve  is  working.    a hissing  noise  will  be  heard  as  air  passes  through  the valve and a strong vacuum should be felt immediately if a finger is placed over the valve Inlet. Replace P.C.V.  valve if necessary. (2) Ventilation hose 1.  Check hoses and hose connections for leaks. 2.  Disconnect all hoses and clean with compressed air. If any hose is not free of obstructions, replace. WARNING Compressed  air  used  for  cleaning  purposes  will not   exceed   30   PSI.      Use   only   with   effective   chip guarding and personal protective equipment (goggles/shield, gloves, etc.). 4 - 16