**I. Will the diesel engine be difficult to start or easily stall if air enters the fuel supply system?** Air has high compressibility and elasticity. When there is a leak in the fuel line from the fuel tank to the diesel engine's fuel pump, air will seep in, reducing the vacuum in this section of the line. This weakens the suction of fuel in the tank, or even causes a complete interruption of fuel flow, preventing the engine from starting. With a small amount of air, the fuel flow can still be maintained and delivered to the injection pump, but the engine may be difficult to start, or it may start but then stall shortly after. When a slightly larger amount of air enters the fuel line, it can cause several cylinders to lose fuel or significantly reduce the amount of fuel injected, making the diesel engine impossible to start. **II. How to find and seal leaks in the fuel lines?** The diesel engine's fuel supply system is divided into low-pressure and high-pressure fuel lines. The low-pressure fuel line refers to the section from the fuel tank to the low-pressure chamber of the injection pump, while the high-pressure fuel line refers to the section from the plunger chamber in the high-pressure pump to the fuel injector. In a plunger pump fuel supply system, air will not seep into the high-pressure fuel line; any leaks will only cause fuel leakage, which can be addressed by plugging the leaks. The following focuses on leaks in the low-pressure fuel line. Diesel engine fuel supply systems often use flexible hoses in the low-pressure fuel line. These hoses are prone to friction with other parts, causing leaks and air intake. Oil leaks are relatively easy to find, but air intake from a broken section of the line is much more difficult. Here are methods for locating leaks in the low-pressure fuel line: Method 1: Bleed the air from the fuel line, start the engine, and locate the point where diesel fuel is leaking; this is the leak point. Method 2: Loosen the bleed screw on the engine injection pump and manually pump fuel. If a large amount of bubbly fuel is emitted from the bleed screw, and the bubbles do not disappear after repeated manual pumping, a leak is confirmed in the negative pressure fuel line between the fuel tank and the fuel pump. This section of the line should be removed, pressurized gas introduced, and the line placed in water. Locate the point where bubbles are emitted; this is the leak point. In addition to pipeline problems, various gaskets at pipeline joints can also leak due to improper installation, deformation, aging, or damage, becoming leak points. Before conducting a detailed inspection of the pipeline, these joints should be checked first. The rigid oil pipe outside the fuel tank is generally less prone to failure. If the above checks still cannot find the leak point, it can be checked last. [b]III. How to remove air from the fuel system?[/b] (1) Conventional method. Use a screwdriver or wrench to loosen any of the bleed screws on the upper side of the fuel injection pump several turns. Press the manual fuel pump by hand until the discharged diesel fuel is continuous, smooth, and free of air bubbles, making a "squeaking" sound. Then tighten the bleed screw and press the manual fuel pump back to its original position. (2) If you are driving and do not have a suitable screwdriver or wrench to open the bleed screw on the fuel injection pump, you can first unscrew the hand pump, then loosen any pipe joint between the diesel filter and the fuel injection pump, and then repeatedly press the hand pump until a smooth, air-free fuel flow comes out of the joint. Then, while pressing the hand pump, tighten the joint, and then press the hand pump back to its original position. (3) If you do not have a wrench to loosen the joints in the pipeline, you can repeatedly press your hand pump until the pressure in the low-pressure fuel line from the fuel pump to the fuel injection pump is high enough. When the pressure is high enough, the fuel will flow from the overflow valve into the fuel return line, and the air in the fuel line will be discharged from the overflow valve. (4) If you need to purge the air in the fuel line while traveling, you can first loosen the bleed screw on the fuel injection pump or loosen any joint between the diesel filter and the fuel injection pump, and then start the mechanical fuel pump. The leak will then spray out a smooth, bubble-free stream of fuel. At this point, simply tighten the leak you just loosened.