(1) Method for Bleeding Low-Pressure Fuel Circuit of Diesel Engine
The BFM1013 diesel engine fuel system uses a unit pump fuel supply system, which has certain special characteristics in terms of purging air from the fuel system. Because the unit injection pump requires high fuel pre-pressure, there are two systems: 0.3MPa and 0.5MPa (for a specific diesel engine, it may only be one of these systems), normally not lower than 0.2MPa (0.3MPa system) and 0.45MPa (0.5MPa system). Therefore, in the 0.5MPa system, the spring force of the return bolt is much greater than that of the inline pump, making purging with a regular hand pump very difficult. If not operated properly, it is difficult to remove air. If the evacuation is incomplete, the diesel engine may have difficulty starting or may not start at all, and it may also cause cavitation erosion in the unit pump and pump chamber.
① Bleeding Methods for BFM1013 Diesel Engine Fuel System If the diesel engine cannot start due to air in the fuel system, the following three bleeding methods are recommended.
a. Before purging, loosen the high-pressure fuel line clamping nut on the injector and use a hand pump to pressurize the fuel to bleed the system until fuel flows out of the entire high-pressure fuel line without any air bubbles. Then tighten the high-pressure fuel line to complete the purging process.
b. Before purging, tighten the high-pressure fuel line nut on the unit pump and use the hand pump (Figure 1-19) to pressurize the fuel and vent until all high-pressure fuel line outlets are filled with fuel without bubbles. Then tighten the high-pressure fuel line nut to complete the purging.
c. Before purging, first loosen the return overflow valve on the low-pressure oil chamber, instead of loosening the bleed screw on the fuel filter as with an inline pump. Then pump fuel to bleed the gas until no air bubbles flow out. After purging, tighten the return overflow valve to complete the purging process.
Note: It is not recommended to frequently use the method of loosening the high-pressure oil pipe to release air.
Of the above purging methods, the first one is the most effective, but it is relatively troublesome and complicated. If you are not very familiar with diesel engines, you need to be careful when using it to avoid damaging the valve cover gasket and causing oil leakage.
Regardless of the method used for purging, it is essential to completely remove air from the fuel system.
Otherwise, starting the diesel engine will be very difficult.
② Other purging methods for unit pump diesel engine fuel systems Some diesel engine unit pump fuel systems have a purging device installed on the diesel fine filter (as shown by the arrow in Figure 1-20), and the purging requirements are as follows.
a.
Loosen the bleed screw on top of the fuel filter and use the hand pump
on the coarse filter to bleed the fuel until the fuel filter is full of
fuel and the fuel flowing out of the bleed screw no longer contains air
bubbles. Then tighten the bleed screw.
b. Loosen the bleed screw plug on top of the unit pump chamber and use a hand pump to bleed the fuel until the pump chamber is full of fuel and no more air bubbles emerge. Then tighten the bleed screw plug.
c. Loosen the connectors between the high-pressure fuel lines and the injectors of each cylinder. Use a hand pump to purge the air from the high-pressure fuel lines until fuel flows out. Then tighten the connectors.
d. After bleeding, wipe off any fuel that has flowed onto the diesel engine and chassis before starting the diesel engine.
e. Do not use the starter motor to pull the diesel engine to bleed the fuel.
f. During bleeding, avoid splashing fuel onto the exhaust pipe, starter motor, and wiring harness (especially connectors). If fuel is accidentally splashed onto these surfaces, wipe them off immediately.
g. Ensure the fuel is clean and free from contamination during the bleeding process.
