The noise nature of the Fuel Pump needs to be diagnosed by classification. Experimental data show that the background noise of the vane pump is 65-75 dB(A) within the normal range, while the abnormal wear sound pressure level is > 85 dB(A) and contains high-frequency harmonics of 1200-2500 Hz (< 500 Hz for healthy pumps). In 2019, the Mercedes-Benz maintenance database analyzed 50,000 cases, and only 42% of the noise over-limit pumps had physical damage (blade clearance > 0.3mm), most of which were caused by assembly resonance or cavitation. For instance, in the actual measurement of the fuel pump noise of the BMW N52 at 87 dB, 73% of the resonance was caused by the loosening of the fuel tank baffle, and the actual failure rate was 27%.
Cavitation whistling has typical characteristics. When the inlet pressure is less than -0.3 bar, the sound pressure of bubble rupture reaches 93 dB(A), and the spectrum is concentrated in the 50-150 Hz range. When the oil temperature is 40℃, the viscosity drops to 0.6cSt, and the probability of cavitation increases by 60%, but it does not necessarily lead to component damage. Tests on the high-pressure pump of Audi EA888 show that short-term cavitation (< 30 minutes per day) affects the service life of the impeller by less than 3%, and if it persists for 6 months, the wear rate will increase by 200%. Honda’s technical notice suggests prioritizing the inspection of the filter element pressure difference. If it is less than 50 kPa, mechanical faults can be ruled out.
Installation defects amplify the noise performance. Insufficient rigidity of non-original brackets causes resonance at 20-80 Hz (the natural frequency of standard parts is 150 Hz), and the vibration acceleration rises from 0.5g to 2.8g. Measured data: Sealing rings with a diameter deviation greater than 1mm increase the probability of abnormal noise by 45% and raise the noise by 12 dB. The Hyundai Elantra NVH report shows that 79% of the “fault noise” disappears after standard installation, and only 21% of the Fuel Pump components need to be replaced.
Current noise reflects potential circuit hazards. The brush arc generates a high-frequency hissing sound of 35 kHz (> 100 mV ripple), which, although without mechanical damage, indicates motor degradation. When the carbon brush wear exceeds 60%, the contact resistance fluctuates by ±0.8Ω, and the coil temperature rise ΔT increases from 28K to 60K, indicating that the probability of magnet demagnetization rises to 68%. Tesla racing data record: After continuous current noise for 3 months, the probability of oil pump failure reaches 83%, and early intervention is required.
The temperature effect causes transient noise. When cold started at -20℃, the viscosity of the grease increases by 300%, with A noise peak of 92 dB(A). A duration of less than 2 minutes is within the safe range. However, if the humming lasts for more than 5 minutes in a high-temperature environment (oil temperature > 80℃), the risk of copper loss will increase by 80%. Volvo’s Arctic test confirmed that only 11% of the cases of noise exceeding the limit in low temperatures had real faults, while the proportion in high-temperature conditions reached 89%.
Quantitative diagnosis needs to be combined with pressure monitoring. When the oscilloscope detects that the fluctuation of track pressure is > ±10 psi (the ISO 15897 standard requires ±3 psi), the correlation between abnormal noise and faults reaches 95%. Conversely, if the pressure is stable (±1.5 psi), 86% of the abnormal noise is caused by external interference. Porsche PIWIS system logic: Prioritize checking the idle flow at 800 rpm. If it is greater than 120 L/h and the variance is less than 5%, disassembly and maintenance can be delayed, saving 60% of ineffective working hours.