The high-frequency abnormal noise of the Fuel Pump usually results from cavitation. When the pumping flow rate exceeds the design value by 30%, the shock wave generated by the rupture of the oil vapor bubble can reach 200MPa (SAE J2745 standard data). For example, for the Walbro GSL392 model equipped with a flow rate of 255L/h, at a pressure of 3.5bar, if the fuel temperature exceeds 50℃ (under normal working conditions, it is 20-40℃), the decrease in viscosity leads to a 47% increase in the cavitation probability. At this time, the noise sound pressure level will rise from 65dB to 82dB. A study by the Society of Automotive Engineers shows that when the remaining fuel in the fuel tank is less than a quarter, the load current of the fuel pump increases by 15%, and the reduced heat dissipation efficiency leads to a threvefold increase in the wear rate of the bearings. This is a typical complaint case from the owners of the 2019 Honda Civic.
Material fatigue is another key factor. After 100,000 kilometers, the brush thickness of the carbon brush motor wears down to the critical value of 0.8mm (3.2mm for new models), and the contact resistance rises from 0.1Ω to 1.5Ω, forcing the motor speed to increase by 12% to maintain the flow rate and causing a characteristic noise of 600-800Hz. The Bosch 044 series has extended its service life from 150,000 kilometers to 250,000 kilometers by switching to a brushless motor design, and the complaint rate of abnormal noise has decreased by 83% (J.D. Power 2022 Reliability Report). Test data shows that when the fuel filter is clogged by 80%, the fluctuation range of the outlet pressure of the fuel pump expands from ±0.2bar to ±1.5bar, which will trigger the resonant frequency of the pump body (usually 350-500Hz), generating a distinct humming sound.
Design flaws should not be overlooked either. For a certain domestic brand model, due to insufficient rigidity of the fuel pump bracket (with an elastic modulus of only 110GPa), a vibration with an amplitude of 0.05mm was generated at 4000rpm. After amplification by the fuel tank, a noise of 90dB was formed. The improved type adopts a 7075-T6 aluminum alloy bracket (with an elastic modulus of 215GPa), combined with rubber shock-absorbing pads, reducing the vibration transmission rate by 78%. The mismatch of Fuel circuit parameters is equally fatal. In 2021, 120,000 pickup trucks were recalled in North America because the pulse width modulation frequency of the high-pressure fuel Pump (HPP) coincided with the 140Hz natural frequency of the low-pressure fuel pump (Fuel Pump), causing the resonance noise to exceed the standard by 12dB.
Maintenance factors directly affect the probability of abnormal noise. Long-term use of E10 ethanol gasoline will cause the plastic parts inside the pump body to swell by 0.3-0.5mm, reduce the impeller clearance from the design value of 0.1mm to 0.05mm, and increase the friction noise by 20dB. Continental’s experiments have proved that for every 10,000 kilometers of delay in replacing the fuel filter, the risk of abnormal noise from the fuel pump increases by 19%. Cost analysis shows that regular maintenance (an average of 300 yuan per year) can avoid the replacement of the fuel pump assembly (with a market price of 1,200-5,000 yuan), and the return on investment reaches 400%. These data reveal the complex mechanisms and coping strategies behind high-frequency abnormal noises.