The intake of air into the diesel fuel pump can cause difficulties in starting and a decrease in power. To troubleshoot the pipeline from the fuel tank to the fuel pump, the following steps should be followed:
1、 Preliminary judgment on whether air has entered
Observe symptoms:
When starting, the motor needs to be turned on multiple times, and there is a phenomenon of "air resistance" in the fuel pipeline (feeling weak or having bubbles when the hand pump pumps oil).
Suddenly stalling during operation, or unstable idling, intermittent loss of power.
Simple testing:
Release the oil pump outlet pipe connector, press the hand pump, and if there are bubbles in the fuel flowing out, confirm the intake of the pipe.
2、 Maintenance steps for oil tank to oil pump pipeline
1. Check the fuel tank section
Fuel tank cap vent hole:
Unscrew the fuel tank cap and observe if the vent hole is blocked (use a thin wire to clear it, or replace the damaged fuel tank cap with a vent hole).
Fuel level and impurities in the fuel tank:
Ensure that the fuel quantity is ≥ 1/4 to avoid the fuel pump being emptied.
Remove the fuel tank drain plug and check if the fuel is cloudy or contains impurities (impurities may clog the filter and cause air intake).
2. Check the oil suction pipeline (from the fuel tank to the fuel pump section)
Pipeline appearance inspection:
Check the pipeline (low-pressure oil pipe) from the fuel tank to the fuel pump for cracks, damage, and loose interfaces (with a focus on inspecting bends and joints).
Rubber pipelines need to pay attention to aging, hardening, and cracking (especially near the engine heat source).
Sealing test:
Negative pressure method: Disconnect the inlet of the oil pump, block one end of the pipeline with a rubber plug, and connect the other end to a vacuum pump. Apply a negative pressure of -0.05MPa and maintain it for 30 seconds. If the pressure rises, it indicates air leakage (bubble method: apply soapy water and observe if it bubbles).
Segmented inspection: Split the pipeline into two sections, from the fuel tank to the filter and from the filter to the oil delivery pump, and test them separately to reduce the range of air leakage.
3. Check the fuel filter
Filter blockage:
Replace the new filter element (diesel filter elements are usually recommended to be replaced every 10000 kilometers). If the old filter element is severely blackened or clumped, it may cause suction due to excessive resistance.
Filter sealing ring:
When disassembling the filter, check whether the sealing ring is deformed or aged (replace the sealing ring, ensure that it is installed in place, and tighten the bolts evenly).
4. Maintenance of oil transfer pump and manual oil pump
Oil pump piston/diaphragm wear:
If you feel low resistance and weak rebound when pressing the hand oil pump, it may be due to worn internal seals of the fuel pump (such as broken piston rings and diaphragms), and the fuel pump needs to be replaced.
Sealing performance of hand oil pump:
Loosen the exhaust screw of the oil pump and press the handle. If there are continuous bubbles and they cannot be completely discharged, it is possible that the manual oil pump body is leaking air (replace the manual oil pump assembly).
3、 Quick exhaust operation
Manual exhaust air:
Loosen the top exhaust screw of the fuel filter, press the hand pump until the fuel flows continuously without bubbles, and tighten the screw.
Release the inlet/outlet pipe joints of the oil pump in sequence, repeat the pumping and exhaust until the pipes are filled with fuel.
Activate auxiliary exhaust air:
Start the engine and idle for 5-10 minutes, observe whether there is abnormal white smoke in the exhaust pipe (incomplete combustion of fuel containing air will produce white smoke), until the white smoke disappears.
4、 Precautions
Prohibit open flame operations: Diesel is a flammable material, and should be kept away from sources of ignition during maintenance to avoid danger caused by fuel leakage.
Pipeline connection specifications: When installing oil pipes, ensure that the interfaces are aligned and the clamping force is moderate (excessive tightening may cause fracturing of the pipeline).
Prioritize replacing vulnerable parts: If troubleshooting is difficult, you can first replace aging rubber pipelines and sealing rings, and then test whether they have returned to normal.
Summary: The inspection of diesel pipeline intake should follow the principle of "simple to complex, segmented testing", focusing on checking the fuel tank ventilation, pipeline sealing, and filter status. If the air intake is repeated after self inspection, it may be due to an internal malfunction of the fuel pump or a broken oil suction pipe inside the fuel tank. Professional personnel need to further disassemble and inspect it.
