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Fuel Injection Equipment and Controls
Figure 3-14.A damaged and serviceable plunger.

Engineman 1 & C - Advanced engine mechanics training manual
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Chapter  3—ENGINE  MAINTENANCE common rail system and the modified common rail  system. The  fuel  injection  systems  used  on  Atlas engines   and   some   older   models   of   Cooper- Bessemer engines are of the basic type. In this system  one  untimed,  high-pressure  pump  supplies fuel at injection pressure to a main header (com- mon rail). The fuel flows from the header to the injector valves and nozzles at each cylinder. The injector  valves  are  cam-operated  and  timed. Metering of the fuel is controlled by the length of  time  the  nozzle  remains  open  and  by  the pressure maintained by the high-pressure pump in the common rail. The modified common rail system (constant pressure),  found  on  newer  models  of  Cooper- Bessemer  engines,  uses  a  high-pressure  pump  to maintain  fuel  at  the  injection  pressure  in  an accumulator   bottle.   The   fuel   is   metered   by individual  valves  mounted  on  the  side  of  the engine;  it  then  flows  to  the  pressure-operated nozzles in the cylinder head, to be atomized and distributed in the cylinder. Since complete details for the maintenance and repair of each of the various fuel systems in serv- ice are beyond the scope of this book, specific information  on  a  particular  fuel  injection  system must come from the appropriate manufacturer’s technical   manual. FUEL INJECTION PUMPS AND INJECTORS In any discussion of a fuel system, the impor- tance of each of its parts cannot be overlooked. The first requirement for trouble-free operation of a fuel system is clean fuel. Accordingly, the filters, the strainers, the tanks, the transfer pumps, and the lines must be maintained according to prescribed instructions. Even when these parts function properly, the principal elements of the injection   system—pressure   pump,   injection valves,  and  injection  nozzles—are  subject  to troubles. The following discussion covers some of these troubles, their symptoms and causes, and provides   general   information   concerning maintenance and repair of this equipment. As you study  this  information,  keep  in  mind  the  dif- ferences which may exist between the various systems. (A system, for example, may be of the jerk pump or common rail type, or the pressure pump  and  the  injector  may  be  separate  or combined.) Damaged  Plunger In the plunger and barrel assembly of a high- pressure pump and in the plunger and bushing assembly of a unit injector, the symptoms and causes of damage are similar. Damage  may  become  apparent  through  erratic engine operation. Symptoms vary widely and may include failure of the engine to develop full power, low  exhaust  temperature,  low  firing  pressure  for the  affected  cylinder,  difficulty  in  balancing (calibrating) the pumps or injectors, and failure of one or more cylinders of the engine to fire. Damage to a plunger and the part in which it slides may also be recognized by testing the unit on a test stand. However, the best way to determine the extent of damage is to disassemble the unit, clean it thoroughly, and then carefully inspect each part. Cleaning of the units can be best accomplished by  use  of  an  approved  solvent.  Clean  diesel  fuel may be used when more effective cleaners are not available. A brush must be used with diesel fuel and even then, removal of gummy deposits is dif- ficult. Keep each plunger and barrel (bushing) together  during  the  inspection  to  avoid  improper assembly, as they are manufactured in matched sets. The  use  of  a  magnifying  glass  during  the examination of a plunger will facilitate the detec- tion of damage. Inspect for fine scratches, dull surface  appearance,  cracks,  pit  marks  (usually accompanied  by  dark  discoloration),  and  erosion and roughness at the edge of the helix or at the end of the plunger. An example of a badly scored plunger  is  illustrated  in  A  of  figure  3-14. A plunger with the lapped surface and helix edge in good condition is shown in B of figure 3-14. Surface irregularities in the region illustrated are serious  because  they  affect  metering  and,  conse- quently, engine operation. When examining a barrel or bushing, search for erosion of the ports or scoring of the lapped surfaces. Pay particular attention to the lapped plane surface at the end of a pump barrel. Rust or pit marks on this surface must be removed by lapping before reassembly. 3-17







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