TM 10-3930-671-24 WARNING Smoking   or   open   flame   should   be avoided  any  time  the  fuel  system  is being serviced or repaired.  The work area   should   be   properly   ventilated. Clean   up   all   fuel   spills.      Improper handling   of   fuel   could   result   in   an explosion or fire causing bodily Injury to yourself or others. Fuel Supply (Transfer) Pump The  electric  fuel  supply  pump  is  a  solenoid-operated, plunger-type pump mounted on the engine cylinder block fuel   pump   pad   and   operated   from   the   truck   battery electrical  system.    It  is  completely  sealed  against  fuel leakage  and  has  the  ability  to  prime  itself  and  the  filter without engine cranking. The  fuel  pump  is  energized  in  the  ignition  circuit  which ensures  prompt  filling  of  the  fuel  filter  and  fuel  line  to effect easy starting. Fuel Pump Troubleshooting When  fuel  pump  trouble  is  suspected,  disconnect  the fuel line at the input side of the fuel injection pump.  Turn ignition  switch  ON.    Pump  fuel  into  a  small  container, then place your finger on the outlet side of the  fuel  line. If  the  pump  stops  or  ticks  very  infrequently,  the  pump and fuel line connections are satisfactory.  Remove your finger  from  the  fuel  line,  and  if  ample  fuel  flows,  the pump is satisfactory. If  the  pump  ticks  (pumps)  with  your  finger  on  the  fuel line,  it  may  mean  that  there  is  a  leak  in  the  fuel  supply line.    Check  for  loose   fittings   or   damaged   fuel   lines. Repair or replace, as necessary. If  the  fuel  does  not  flow  and/or  the  pressure  is  below 1.50-2.25  psi  [77-116  mm  Hg]    range,  the  pump  should be replaced. WARNING Before disconnecting lines, be sure to relieve all pressure.        Before    applying    pressure    to    the system,   be   sure   all   connections   are   tight   and that   lines,   pipes   and   hoses   are   not   damaged. Use  a  piece  of  cardboard,  rather  than  hands,  to search for leaks.  Escaping fluid under pressure can  have  sufficient  force  to  penetrate  the  skin, causing  personal  Injury.    If  Injured  by  escaping fluid, get medical attention at once. Priming the Fuel System Priming   is   necessary   on   initial   installation   of   the   fuel injection  system,  after  any  subsequent  removal,  and  if the  system  should  be  drained  by  running  out  of  fuel. Before priming and venting the fuel system, be sure that the  outside  of  the  vent  screws  and  surrounding  area  is thoroughly  clean  to  prevent  dirt  and  foreign  matter  from entering the system. NOTE Electrical equipment such as starters should   be   shielded   to   prevent   fuel damage during priming. 1. Loosen  the  filter  outlet  (A),  or  the  fuel  injection pump  inlet  connection  (B)  whichever  is  at  the highest  point,  and  allow  fuel  to  flow  until  free  of air.  Tighten connections. NOTE Filters   of   the   four-boas   type   must also  be  vented  at  the  plugged  boss; this  must  be  done  regardless  of  the height of the filter in the system. 2. Loosen  the  vent  valve  fitted  on  one  of  the  two hydraulic head locking screws  (C),  and  the  vent screw  (D)  on  the  governor  housing.    When  fuel free   of   air   flows   from   the   vents,   tighten   the housing  vent  screw  and  then  the  governor  vent screw. F-203