TM 5-3825-226-24 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 head C.  Check for rough or poorly machined gasket.   head or block surfaces.  Replace necessary components. FUEL SYSTEM Either    too    much    fuel    or    not    enough    fuel    for combustion  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 priming pump and loosen the nuts holding the fuel lines to  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