First, the inspection and evaluation of the condition of components.
1. Checking and assessing the technical condition of the plunger.
(1) Visual inspection: Look for the most worn areas on the plunger and use your fingernail to feel if there's a distinct texture when you run it across. If so, replace it with a new one.
(2) Empirical test: Clean the plunger with diesel fuel and fill the sleeve with diesel as well. Block the oil inlet, return, and center holes with your finger, then pull out the plunger. After releasing, if it returns within 1/3 of its length, it can still be used; otherwise, it should be replaced.
(3) Pressure gauge method: Connect a pressure gauge to the pump head, set the throttle to maximum fuel supply, activate decompression, and crank the engine to make the plunger pump oil at 30 strokes per minute. The pressure must exceed 19.6 kPa; otherwise, replace the plunger.
2. Checking and evaluating the condition of the fuel valve.
(1) Visual inspection: Check the sealing ring. If it is sunken and its width exceeds 0.5 mm, or if the decompression band has noticeable wear marks and no original shiny surface remains, replace it.
(2) Oil pressure test: Remove the high-pressure fuel pipe of the cylinder being tested, open the injection pump inspection window, move the plunger to the bottom dead center, and pump fuel manually. First, purge the air in the system, then check for leaks at the high-pressure tube joint. If any leakage occurs, replace the part (this method does not test the decompression ring).
(3) Pressure gauge inspection: This test should be done together with the plunger pressure check. When the pressure drops from 19.6 kPa to 17.65 kPa, the time taken for the pointer to stabilize should be over 15 seconds, indicating good sealing. If the pressure rises to 24.52 kPa and then cuts off, observe the rebound of the hand. A rebound between 0.98–6.87 kPa indicates normal decompression. Only when the seal is good can the exact rebound value be measured.
If faults remain after the above checks, remove the fuel valve and inspect for wear after cleaning. If no obvious grooves are found, the high-pressure copper gasket may not be worn. Usually, after cleaning, tightening the seal surface will restore normal function. Otherwise, replace the part.
3. Inspecting and evaluating the condition of the fuel injector.
This inspection should only be performed when the plunger pair and outlet valve are functioning properly.
(1) In-vehicle testing: If the rest of the engine is working normally, install the fuel injector after rough adjustment. Start the engine and adjust it by listening to sounds and observing the exhaust.
(2) Standard nozzle comparison: Use a standard nozzle that has been pre-adjusted to compare with the one being tested. Connect both nozzles in parallel to the fuel pump via a three-way pipe, purge the air, and set the throttle to maximum. Open the decompression lever and observe whether both nozzles spray simultaneously. If they do, or if they stop at the same time, and the atomization is the same, the tested injectors are qualified.
(3) Pressure gauge test: Connect the pressure gauge and the injector to be tested in parallel with the fuel injection pump using a tee pipe. Set the throttle to maximum, activate decompression, and pump fuel until the pressure reaches 9.8 kPa (adjusted according to the pressure regulator spring). The injectors should spray about 10 times per minute without dripping. After this, adjust the needle valve to the specified pressure and perform an atomization test at around 80 strokes per minute. The droplets should be fine, evenly distributed, with the correct cone angle and a crisp oil beam cut, accompanied by a sharp sound.
If problems persist after these tests, disassemble and clean the needle valve, plunger, and spring. If serious wear prevents normal operation, replace the parts.
Second, extending the life of the components.
Besides product quality issues, the main cause of coupling damage is improper machine use and incorrect or inaccurate maintenance. Here are some measures to help extend the life of the components.
1. Strictly follow the fuel sedimentation and filtration system. Diesel should be collected after 48 hours of settling. The diesel used must meet seasonal standards. Refueling tools must be kept clean, and refueling and storage areas should also be kept clean to prevent dirt from mixing with the fuel, which can accelerate wear and reduce component lifespan.
2. Implement strict technical maintenance procedures. Replace the fuel filter every 100 hours and the fuel tank every 500 hours. If the filter element is damaged, replace it immediately—never bypass it or use direct fuel supply. Disassemble and inspect the coupling once every 500 hours under normal conditions. During disassembly, ensure the work area, hands, tools, and cleaning oil are all clean to avoid contaminating the parts. Avoid tapping or damaging during disassembly. Do not wash parts randomly or mix them with other components. During assembly, never change positions arbitrarily or adjust parts that don’t align with the machine’s requirements. When installing the valve seat and nozzle cap, tighten them to the specified torque to ensure the fuel injector and pump are in good condition.
3. In addition to the above, improve your understanding of dual-part systems. Learn their structure and working principles, strengthen maintenance, and operate them correctly. Avoid making arbitrary adjustments or disassemblies when no fault exists. Don’t knock, clean, or rub parts indiscriminately during maintenance. Don’t change screw positions randomly during assembly or adjustment. Always follow technical specifications to achieve the goal of extending the service life of the components.
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