Common faults and solutions of fuel injectors

The fuel injector is a precision device with very high precision (the most precise of which is the most precise needle valve and needle valve body), which mainly accepts the fuel injection pulse signal sent by the ECU, and precisely controls the fuel injection volume.

　　 The failure of the injector is basically caused by the influence of the dirt in the diesel engine. The main reason is that the injector head in the combustion chamber has been in a high temperature and high pressure environment for a long time. Due to the influence of thermal expansion and contraction, the needle valve slowly expands and deforms or the fuel injection port is blocked by carbon deposits, and the fuel injection volume Decrease, and gradually fail to inject fuel normally, which affects the normal operation of diesel engines. General injector failures have the following points. Now the common failures and troubleshooting methods of injectors are introduced as follows.

　　 When the fuel injection pressure is too low, the nozzle hole wears and there is carbon deposits, the spring end surface is worn or the elasticity drops, it will cause the fuel injector to open in advance, delay the closure, and cause the phenomenon of poor fuel injection atomization. If it is a single-cylinder diesel engine, it will not work, while a multi-cylinder diesel engine will lose power, emit black smoke from the exhaust, and make the machine run abnormally. In addition, because diesel mist droplets with an excessively large particle size cannot be fully burned, they flow into the oil accumulation pan along the cylinder wall, which increases the oil level, decreases the viscosity, and deteriorates lubrication, which may also cause the burning of the cylinder. Solution: The injector should be disassembled and cleaned, repaired, and re-commissioned.

　　 When the needle valve assembly is severely worn or the needle valve body and the injector housing are not tightly matched, the oil return of the injector will increase significantly, and some can reach 0.1 ~ 0.3 kg/h. If the return pipe is damaged or missing, the return oil will be lost in vain, resulting in waste. Therefore, the oil return pipe must be intact and installed airtight so that the return oil can flow into the oil tank smoothly. If the oil return pipe is connected to the diesel filter, the terminal should be equipped with a one-way valve to prevent the diesel in the filter from flowing back into the fuel injector.

　　 Due to the continuous injection of high-pressure oil flow, the needle valve nozzle hole will gradually become larger, resulting in a drop in fuel injection pressure, shorter injection distance, poor diesel atomization, and increased carbon deposits in the cylinder.

Solution: The diameter of the single-hole shaft needle injector is generally larger than 1 mm, and a steel ball with a diameter of 4 to 5 mm can be placed at the end of the hole and tapped with a hammer to make the injection hole partially plastically deformed and shrink Aperture. Due to the large number of holes and the small diameter of the multi-hole direct injection injector, it can only be tapped lightly on the hole end with a punch made of high-speed steel. If it is still unqualified after debugging, the needle valve assembly should be replaced.

Moisture or acidic substances in diesel will cause the needle valve to rust and become stuck. After the needle valve sealing cone is damaged, the combustible gas in the cylinder will flow into the mating surface to form carbon deposits, causing the needle valve to seize and the fuel injector. The fuel injection effect is lost, causing the cylinder to stop working.

Solution: Put the needle valve assembly in the waste engine oil and heat it until it boils and smoke, and then take it out. Use the pliers padded with a soft cloth to clamp the needle valve tail and move it slowly, then pull it out and stain it with clean engine oil. The needle valve moves and grinds repeatedly in the valve body until the needle valve can slowly withdraw from the valve body when the needle valve assembly is turned upside down. If the fuel injector fails to pass the test, the needle valve assembly should be replaced.

　　The end face of the needle valve body is impacted by the frequent reciprocating movement of the needle valve. Over time, pits will gradually form, which will increase the lift of the needle valve and affect the normal operation of the injector.

　　Solution: The needle valve body can be clamped on a grinder to grind the end surface, and then use a fine grinding paste to grind the glass plate.

　　 When installing the injector on the cylinder head, the carbon deposit in the mounting hole should be carefully removed. The copper gasket must be flat and must not be replaced with asbestos or other materials to prevent poor heat dissipation or failure to seal. If the copper washer is made by yourself, it must be processed with red copper according to the specified thickness to ensure that the distance from the injector to the plane of the cylinder head meets the technical requirements. For example, the distance of the 135 series diesel engine is 1.5-2 mm, too large or small will affect the cylinder compression ratio. In addition, the concave shape of the pressure plate of the injector should be installed downwards. Avoid unilateral bias when tightening. It should be evenly tightened according to the specified torque, otherwise the injector head will be deformed and deflected and cause gas leakage and oil leakage.

The frequent reciprocating movement of the needle valve in the needle valve hole, coupled with the intrusion of impurities and dirt in the diesel oil, will gradually wear the guide surface of the needle valve hole, resulting in an increase in the gap or scratches, resulting in an increase in the internal leakage of the injector and the pressure Decrease, the amount of fuel injection is reduced, and the fuel injection time lags, causing difficulty in starting diesel engines.

　　 Solution: When the fuel injection time is delayed too much, the locomotive cannot even run, and the needle valve assembly should be replaced at this time.

When the fuel injector is working, the sealing cone of the needle valve body will be subject to frequent and strong impacts from the needle valve. Coupled with the continuous injection of high-pressure oil from there, the cone will gradually appear nicks or spots, which will lose the seal and cause The injector is dripping oil. When the temperature of the diesel engine is low, the exhaust pipe emits white smoke, and when the engine temperature rises, it turns into black smoke, and the exhaust pipe emits irregular firing sounds. If the oil supply to the tank is stopped at this time, the smoke exhaust and the sound of shooting will disappear.

Solution: The fuel injector can be disassembled, and a little chromium oxide fine grinding paste is applied to the needle valve head (be careful not to stick in the needle valve hole) to grind the cone surface, then wash it with diesel oil, and put it into the fuel injector for testing . If it still fails, you need to replace the needle valve assembly.

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