(1) Common faults of fuel injectors and their repair methods
The working conditions of the injector are very bad, the mechanical load and the heat load are high, and the improper installation and adjustment often lead to malfunctions such as poor spray, dripping oil, carbon deposits, and even needle stuck.
1 The injector does not spray oil. Check whether there is air in the oil circuit, if there is air in time; whether the oil supply to the oil pump is normal; whether the fuel system leaks oil; whether the fuel injection needle is stuck in the needle valve hole, and if necessary, disassemble and clean it.
2 sealing cone wear. Generally, the valve body cone angle is 590, and the needle valve cone angle is 600, and the contact surface width is 0.2-0.3 mma. If the fuel entering the injector nozzle contains particulate mechanical impurities, the tapered surface will grind the groove mark and contact. When the belt is widened, the fuel leaks oil from the seat surface, causing coke deposits, difficulty in starting, black smoke, power drop, and increased fuel consumption. Maintenance should be cleaned frequently and replaced if necessary. The check of the needle valve is shown in Figure 33.
The 3-needle valve guide surface is worn. The needle valve body has a small clearance of about 0.002 to 0.004 mm. If the surface of the two parts is invaded by dust and mechanical impurities, the geometric accuracy and roughness of the guiding surface will be destroyed, and the contact surface will generate high pressure and instantaneous high temperature. The surface is stuck and worn and jammed. In this case, new parts should be replaced.
4-axis needle and nozzle hole wear. Fuel is washed at a higher pressure and speed, which is the main cause of wear on the needle shaft of the needle valve and the nozzle hole of the valve body. At the same time, the nozzle part of the shaft needle extends into the combustion chamber to contact with the combustion gas, which makes the surface become brittle, and the sparse or comb-like groove marks are generated. The shaft needle is changed from the original cylindrical shape to the conical shape, and the orifice diameter of the injection hole is also increased and lost. The positive ring shape causes the injection pressure to drop, the spray quality to deteriorate and the injection time to be shortened, and the replacement should be repaired.
5 The spring of the pressure regulating spring is insufficient. The injection pressure of the injector is too low, the fuel atomization is poor and cannot be adjusted, and even the compressed gas in the cylinder is opened to the injector needle, and the oil return pipe is passed to the high pressure oil pump, so that the diesel engine is turned off without pumping oil. In this case, the pressure regulating spring should be updated. In the case that no new pressure regulating spring can be replaced, a small gasket 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 to solve the problem. The problem of insufficient elasticity.
(2) Inspection and adjustment of the injector
1 The injector does not work properly, which usually causes the injector to work badly. Therefore, in addition to checking the use of other parts of the injector one by one, it is necessary to focus on the injector accident. The nozzle face of the injector and the end face of the needle valve should be bright and bright, no damage, no rust, and the sealing surface of the needle valve and the needle valve body should be bright, no pitting, no scratches.
The 2-needle valve and the needle valve body are paired and ground and can not be interchanged. Therefore, when cleaning, do not mix and disassemble, and clean them separately; when the needle valve is stuck in the needle valve body, it should be replaced.
The carbon deposits of the 3-needle valve and the needle valve body can only be removed with special tools, but special care must be taken not to hurt the mating surface.
4 Install the fuel injector on the tester, press the oil evenly and slowly with the handle (see Figure 34), and screw the adjusting screw until the injector is sprayed under the specified pressure. Stop the oil pressure and observe whether the pointer of the pressure gauge drops (and there is no dripping phenomenon); the difference of the injection pressure of each injector 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 the specified value.
5 spray quality inspection (see Figure 35): the injector should generally have 4 sprays, each spray length is about 150-200mm, the fuel mist cone sprayed from the injector should not be skewed, and the cone should conform to the original factory. Provisions. When slowly pressing the oil with the handle, the oil mist sprayed from the nozzle should be fine. The oil particles in the mist of each oil hole should be evenly distributed and the length should be uniform. There should be no oil mist splash and oil column visible to the naked eye. Or dripping phenomenon; the fuel cut should be timely and have a crisp sound. If the spray quality is not good, the grease nozzle should be replaced.
6 Injector fault detection on the engine: Once the injector malfunctions, the running engine will generate exhaust smoke, black cylinders, uneven operation, increased vibration, and reduced power. The broken cylinder method can be used in turn to find the faulty injector. The method is: the engine is running at an idle speed, and the fuel injection of each cylinder is stopped in turn. When a cylinder stops supplying oil, if the exhaust gas no longer emits black smoke, the engine speed changes are not obvious, and the injector nozzle is faulty; if the engine speed is significantly decreased The working condition has become bad, and the injector nozzle is working properly.