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Common faults and maintenance of fuel injectors


The fuel injector is composed of a fuel injector body, a tappet, a fuel injector coupling piece, a pressure regulating spring and other parts. When working, the fuel injection pump draws high-pressure fuel from the fuel injector inlet pipe joint through the fuel injector body and the needle valve body. The oil passage enters the annular high-pressure oil chamber in the middle of the needle valve body, and the oil pressure acts on the pressure-bearing slope in the middle of the needle valve to form an upward axial thrust. When the thrust exceeds the pressure of the pressure regulating spring, the needle valve moves upward , The fuel passes through the four nozzle holes at the bottom of the valve body and sprays into the combustion chamber in an atomized state. When the fuel supply is interrupted and the oil flow pressure drops, the needle valve quickly returns to its position under the action of the pressure regulating spring. The sealing cone at the lower part of the needle valve presses against the sealing cone of the needle valve body and closes the nozzle hole, and the fuel injection stops. 

    (1) Common faults and maintenance methods of fuel injectors

    The working conditions of the fuel injector are very bad, the mechanical load and thermal load are high, coupled with improper installation and adjustment, there will often be failures such as poor spraying, dripping of the nozzle, carbon deposits, and even the needle valve stuck.

    ①The fuel injector does not inject fuel. Check whether there is air in the oil circuit. If there is air, remove it in time; whether the fuel supply of the fuel pump is normal; whether the fuel system is leaking; whether the fuel injection needle valve is stuck in the needle valve hole, if necessary, remove it and clean it for repair.

    ②The sealing cone is worn. Generally, the cone angle of the valve body is 590, while the needle valve cone angle is 600, and the contact surface width is 0.2-0.3mma. If the fuel entering the fuel injector contains particulate mechanical impurities, the conical surface will wear groove marks and contact When the belt is widened, the fuel will leak and drip from the seat surface, causing coke and carbon deposits, difficult starting, black smoke, power drop, and fuel consumption increase. It should be cleaned and maintained frequently, and replaced when necessary. Check the needle valve fit as shown in Figure 33

   ③The guide surface of the needle valve is worn. The matching clearance of the needle valve body is very small, only about 0.002 to 0.004mm. If the surfaces of the two parts are invaded by dust and mechanical impurities, the geometric accuracy and roughness of the guide surface will be destroyed, and the contact surface will generate high pressure and instantaneous high temperature. Causes the surface to stick to wear and get stuck. In this case, new parts should be replaced.

    ④Axle needle and nozzle are worn out. Fuel scours at higher pressure and speed, which is the main cause of wear of needle valve shaft and valve body nozzle. At the same time, the nozzle part of the shaft needle extends into the combustion chamber to contact the combustion gas, making the surface brittle, resulting in peeling or comb-like groove marks. The shaft needle head changes from a cylindrical shape to a conical shape, and the nozzle hole diameter is also worn and lost. The positive circle shape causes the fuel injection pressure to drop, the spray quality deteriorates and the fuel injection time is shortened, and should be replaced and repaired.

    ⑤The elastic force of the pressure regulating spring is insufficient. The injection pressure of the injector is too low, and the fuel atomization is poor and cannot be adjusted. Even the compressed gas in the cylinder pushes the injector needle valve and passes through the oil return pipe to the high-pressure fuel pump, causing the diesel engine to stall without pumping oil. In this regard, the pressure regulating spring should be updated. In the case that there is no new pressure regulating spring to replace, a small washer of appropriate thickness can be added between the original pressure regulating spring and the pressure regulating spring seat to increase the preload of the spring. The problem of insufficient elasticity.

 (2) Inspection and adjustment of the fuel injector

    ① Abnormal operation of the fuel injector usually results in the malfunction of the fuel injector. Therefore, in addition to checking the use of other parts of the fuel injector one by one, the fuel injector should be overhauled. The mating surface of the fuel injection nozzle and the end surface of the needle valve should be bright in color, free of damage and corrosion, and the sealing cone of the needle valve and needle valve body should be bright, free of pitting or scratches.

    ②The needle valve and the needle valve body are paired and ground and cannot be interchanged. Therefore, they should not be mixed during cleaning. They must be cleaned separately in pairs; the needle valve should be replaced when it is stuck in the needle valve body.

   ③Carbon deposits on the needle valve and the needle valve body can only be removed with special tools, but special care should be taken not to damage the mating surface.

    ④ Install the fuel injector on the tester, press the oil evenly and slowly with the handle, and at the same time screw the adjusting screw until the fuel injector sprays oil under the specified pressure. Stop oil pressure and observe whether the pointer of the pressure gauge drops (and there is no dripping phenomenon); the fuel injection pressure difference of the fuel injection nozzles of the same engine must not exceed the specified value. If the pressure does not meet the requirements, the pressure regulating spring screw can be rotated to adjust to the specified value value.

    ⑤ Inspection of spray quality: Generally, the fuel injector should have 4 sprays, each of which is about 150-200mm in length. The fuel mist cone sprayed from the fuel injector should not be skewed, and the cone should comply with the original factory regulations. When pressing the oil slowly with the handle, the oil mist sprayed from the nozzle should be fine, and the oil particles in each oil hole mist beam should be evenly distributed and the length should be the same. There should be no visible oil mist splashing and oil particle columns. Or dripping phenomenon; fuel cut off should be timely, and there should be a crisp sound. If the spray quality is not good, replace the fuel nozzle

    ⑥ Inspection of fuel injector failure on the engine: Once the fuel injector fails, the running engine will produce black smoke from exhaust, uneven work of each cylinder, increased vibration, and power drop. The broken cylinder method can be used in turn to find out the malfunctioning injector. The method is: the engine is running at idling speed and the fuel injection of each cylinder is stopped in sequence. When a cylinder stops supplying fuel, if the exhaust no longer emits black smoke and the engine speed does not change significantly, the fuel injector is malfunctioning; if the engine speed drops significantly , The working condition has become bad, for this cylinder injector is working normally.

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