TM 5-3805-260-24SYMPTOMSCAUSEREMEDY36. Compressor head gasketA.Restricted discharge line.A.Clear restriction or replace line.failure.B.Loose head bolts.B.Tighten evenly to a torque of 25-30 footpounds.C.Faulty compressor or C.Check for rough or poorly machinedhead gasket.head or block surfaces. Replace necessarycomponents.FUEL SYSTEMEither 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 systemwhen the problem is really with some other part of theengine. The source of the problem is difficult to find,especially when smoke comes from the exhaust. Smokethat comes from the exhaust can be caused by a badfuel injection valve, but it can also be caused by one ormore 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 INSPECTIONA problem with the components that send fuel tothe engine can cause low fuel pressure. This candecrease engine performance.1.Check the fuel level in the fuel tank. Lookat the cap for the fuel tank to make sure thevent is not filled with dirt.2.Check the fuel lines for fuel leakage. Besure the fuel supply line does not have arestriction or a bad bend.3.Install a new fuel filter. Clean the fuelscreen located in the inlet valve of the fueltransfer pump.4.Remove any air that may be in the fuelsystem. If there is air in the fuel system, use the prim-ing pump and loosen the nuts holding the fuel lines torthe outside of the cylinder head, one at a time. Do thisuntil fuel, without air, comes from the fuel lineconnection.CHECK ENGINE CYLINDERS SEPARATELYAn easy check can be made to find the cylinderthat runs rough (misfires) and causes black smoke tocome 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 willstop the flow of fuel to that cylinder. Do this for eachcylinder until a loosened fuel line is found that makes nodifference in engine performance. Be sure to tighteneach fuel line nut after the test before the next fuel linenut is loosened. Check each cylinder by this method.When a cylinder is found where the loosened fuel linenut does not make a difference in engine performance,test the injection pump and fuel injection nozzle for thatcylinder.Temperature of an exhaust manifold port, whenthe engine runs at low idle speed, can also be anindication of the condition of a fuel injection nozzle. Lowtemperature at an exhaust manifold port is an indicationof no fuel to the cylinder. This can possibly be anindication of a nozzle with a defect. Extra hightemperature at an exhaust manifold port can be anindication of too much fuel to the cylinder, also caused bya nozzle with a defect.The most common defects found with the fuelinjection valves are:1.Carbon on tip of the nozzle or in the nozzleorifice.2.Orifice wear.CAUTIONDo not test or disassemble nozzles unless youhave the correct service tools.NOTE: Do not disassemble fuel nozzles before theyhave been tested. See TESTING PENCIL-TYPE FUELINJECTION NOZZLES.2-38
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