TM 5-3805-260-24 SYMPTOMS CAUSE REMEDY 36.  Compressor head gasket A. Restricted discharge line. A. Clear restriction or replace line. failure. B. Loose head bolts. B. Tighten evenly to a torque of 25-30 foot pounds. C. Faulty compressor or C. Check for rough or poorly machined head gasket. head or block surfaces.  Replace necessary components. FUEL SYSTEM Either too much fuel or not enough fuel for com- bustion can be the cause of a problem in the fuel system. Many   times   work   is   done   on   the   fuel   system when  the  problem  is  really  with  some  other  part  of  the engine.    The  source  of  the  problem  is  difficult  to  find, especially when smoke comes from the exhaust.  Smoke that  comes  from  the  exhaust  can  be  caused  by  a  bad fuel injection valve, but it  can  also  be  caused  by  one  or more of the reasons that follow: a. Not enough air for good combustion. b. An overload at high altitude. c. Oil leakage into combustion chamber. d. Not enough compression. FUEL SYSTEM INSPECTION A problem with the components that send fuel to the   engine   can   cause   low   fuel   pressure.      This   can decrease engine performance. 1. Check  the  fuel  level  in  the  fuel  tank.    Look at the cap for the fuel tank to make sure the vent is not filled with dirt. 2. Check  the  fuel  lines  for  fuel  leakage.    Be sure  the  fuel  supply  line  does  not  have  a restriction or a bad bend. 3. Install   a   new   fuel   filter.      Clean   the   fuel screen located in  the  inlet  valve  of  the  fuel transfer pump. 4. Remove any air that may be in the fuel system.    If  there  is  air  in  the  fuel  system,  use  the  prim- ing  pump  and  loosen  the  nuts  holding  the  fuel  lines  tor the outside of the cylinder head, one at a time.   Do  this until     fuel,     without     air,     comes     from     the     fuel     line connection. CHECK ENGINE CYLINDERS SEPARATELY An easy check can be made to find the cylinder that  runs  rough  (misfires)  and  causes  black  smoke  to come out of the exhaust pipe. Run the engine at the speed that is the roughest. Loosen the fuel line nut at a fuel injection pump.  This will stop  the  flow  of  fuel  to  that  cylinder.    Do  this  for  each cylinder until a loosened fuel line is found that makes no difference  in  engine  performance.    Be  sure  to  tighten each  fuel  line  nut  after  the  test  before  the  next  fuel  line nut  is  loosened.    Check  each  cylinder  by  this  method. When  a  cylinder  is  found  where  the  loosened  fuel  line nut  does  not  make  a  difference  in  engine  performance, test  the  injection  pump  and  fuel  injection  nozzle  for  that cylinder. Temperature of  an  exhaust  manifold  port,  when the   engine   runs   at   low   idle   speed,   can   also   be   an indication of the condition of a fuel injection nozzle.  Low temperature at an exhaust manifold port is an indication of   no   fuel   to   the   cylinder.      This   can   possibly   be   an indication    of    a    nozzle    with    a    defect.        Extra    high temperature   at   an   exhaust   manifold   port   can   be   an indication of too much fuel to the cylinder, also caused by a nozzle with a defect. The  most  common  defects  found  with  the  fuel injection valves are: 1. Carbon on tip of the nozzle or in the nozzle orifice. 2. Orifice wear. CAUTION Do not test or disassemble nozzles unless you have the correct service tools. NOTE:    Do  not  disassemble  fuel  nozzles  before  they have  been  tested.    See  TESTING  PENCIL-TYPE  FUEL INJECTION NOZZLES. 2-38