F U E L S Y S T E MTM 5-3805-258-24-1T E S T I N G A N D A D J U S T I NGFUEL SYSTEMEither too much fuel or not enough fuel for com-bustion can be the cause of a problem in the fuelsystem.Many times work is done on the fuel system whenthe 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.Smoke that comes from the exhaust can be caused bya bad fuel injection valve, but it can also be caused byone 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.e. Fuel injection timing retarded.FUEL SYSTEM INSPECTIONTo check for low fuel pressure, remove 1/8” pipe plug(1). Connect the 8M2743 Gauge from the 5P6225Hydraulic Test Box to the hole where the plug (1) wasremoved. Run the engine at high idle and check the fuelpressure reading. The fuel pressure must beat least 105kPa (15 psi).L O C A T I O N O F F U E L P R E S S U R E S W I T C H1. Fuel pressure switch.A 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. Look at thecap for the fuel tank to make sure the vent is notfilled with dirt.2. Check the fuel lines for fuel leakage. Be sure the4-53.4.fuel supply line does not have a restriction or abad bend.Install a new fuel filter. Clean the primary fuelfilter.Remove any air that may be in the fuel system. Ifthere is air in the fuel system, use the-primingpump and open the drain valve on the fuel injec-tion pump housing until fuel without air comesfrom the drain line.CAUTIONWhen fuel injection lines are loosened or tight-ened on the fuel injection nozzles, twowrenches must be used. The nozzle must beheld with a wrench or damage to the nozzle canresult.To remove air from the fuel injection lines, loosenthe fuel line nuts on the fuel injection nozzles 1/2turn. Move the governor lever to the low idle position.Crank engine with the starter motor until fuel with-out air comes from the fuel line connections. Tightenthe fuel line nuts.NOTE: The fuel priming pump will not give enoughpressure to push fuel through the reverse flow checkvalves in the fuel injection pumps.CHECKING ENGINE CYLINDERSSEPARATELYAn 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. Thiswill stop the flow of fuel to that cylinder. Do this foreach cylinder until a loosened fuel line is found thatmakes no difference in engine performance. Be sureto tighten each fuel line nut after the test before thenext fuel line nut is loosened. Check each cylinder bythis method. When a cylinder is found where theloosened fuel line nut does not make a difference inengine performance, test the injection pump and fuelinjection nozzle for that cylinder.Temperature of an exhaust manifold port, when aengine runs at low idle speed, can also be an indica-tion of the condition of a fuel injection nozzle. Low
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