TM 10-3930-671-24 Smoking   or   open   flame   should   be avoided  any  time  the  fuel  system  Is being repaired or serviced.    The  area should be property ventilated. Improper handling of fuel could result in an explosion or fire causing bodily injury to yourself or others. The basic purpose of the fuel system is to store, convey, and  inject  the  fuel  into  the  engine.    The  fuel  transfer pump   draws   the   fuel   from   the   supply   tank,   forces   it through  the  filters,  and  delivers  it  to  the  injection  pump. The fuel injection pump places it under the high pressure required for mechanical atomization, meters it with great accuracy,  distributes  it  in  the   proper   sequence   to   the various  cylinders,   commences   the   individual   injections with   fine   precision   in   timing,   and   produces   uniformly, through  the  nozzles,  the  correct  pattern  of  spray  for  the combustion chamber. The   injection   system   of   a   diesel   engine   includes   an injection  pump  assembly  complete  with   govemor,   fuel supply    pump,    fuel    filters,    high-pressure    steel    lines connecting  the  pump  discharge  outlets  to  the  nozzles, and nozzle holders and nozzle assemblies, one for each cylinder.        Not    the    least    of    these    are    the    filtration elements, as fine particles of dirt in the fuel are extremely destructive to high-pressure pumps of any description. Carelessness or too frequent removal of elements of the fuel   injection   system   for   "inspection"   or   "cleaning"   is generally  far  more  harmful  than  beneficial,  due  to  the danger  that  dirt  will  enter  the  exposed  connections  and the possibility of mishandling the equipment through lack of  knowledge  of  its  design  and  construction.    Various components   are   made   with   the   utmost   precision   and may be easily damaged when removed. There  should  be  no  tampering  with  the injection pump assembly, or removal of It for inspection, unless engine operation is seriously  Impaired  and  the  cause  of  the difficulty Is directly traceable to the pump unit. It  should  be  borne  in  mind  that  minor  troubles,  such  as suction leaks at joints in the supply line can cause erratic engine  behavior.    It  is  unlikely  that  the  injection  pump itself    would    require    overhaul    before    it    has    several thousand hours of operation.  All injection pumps should be calibrated and repaired at authorized service stations, unless  factory  trained  personnel  are  available  with  the proper tools and test equipment. ELECTRIC FUEL TRANSFER PUMP Many   Continental   TMD   Industrial   engines   use   electric fuel pumps to transfer fuel from the fuel tank to the fuel injection    pump.        These    electric    pumps    are    usually mounted to the crankcase fuel pump pad cover where a mechanical fuel pump would normally be mounted. Electric  fuel  pumps  will  operate  without  having  to  crank the   engine   over.      This   makes   them   extremely   useful when bleeding the air from the fuel system (see Bleeding the  Fuel  System).    They  draw  little  battery  current  and only a slight drain is usually seen on the storage battery during the bleeding process. When fuel pump trouble is suspected, always check that the  pump  is  getting  voltage  from  the  ignition  circuit  and that the BLACK ground wire is intact before declaring the pump  is  bad!  A  "quick"  test  for  voltage  is  to  turn  the ignition switch "on" and feel the body of the pump.  You can actually feel the pump operating and hear it ticking if the work area is quite  enough.    If  you  can’t  hear  or  feel the fuel pump operating, check for actual battery voltage to the unit before declaring it to be bad Using a Voltmeter or test light, check for voltage at the first wire connection closest  to  the  electric  fuel  pump.      This   connection   is usually   found   at   the   fuel   shutoff   solenoid   on   the   fuel injection pump. If no voltage is present - check the  equipment  electrical circuit  for  blown  fuses;  broken  wires;  bad  switches;  etc. If voltage is present at the fuel pump, make one last test before  declaring  the  pump  bad  l  Loosen  the  fuel  line fitting  on  the  inlet  fuel  line  on  the  injection  pump.    Fuel should  flow  and  the  pump  should  begin  ticking  if  it  is operating properly. If the pump is operating, but volume or flow needs to be checked  -  simply  disconnect  the  fuel  inlet  line  from  the fuel injection pump and turn the ignition switch on. F-151 Section 5 - Fuel System