When the Fuel Pump experiences pressure drop during idle speed, it may be due to mechanical wear, system leakage or circuit problems. For instance, the design life of a specific fuel pump brand would normally be 80,000 to 120,000 kilometers. But if the poor-quality fuel (sulfur content above 50ppm) is utilized in the long term, the deterioration rate of the inner carbon brushes could be 30% to 50% greater, and thus the motor speed goes down from the normal value of 3,000 RPM to below 2,000 RPM. The fuel pressure supply of 2.5-3.5bar required to maintain the idle speed cannot be maintained. In 2021, a car manufacturer recalled 120,000 vehicles because of faulty fuel pump impeller designs. Statistics show that the failure rate of idle pressure fluctuations above ±0.5bar accounted for 67% of recalled vehicles.
The clogging of the fuel filter is also another crucial consideration. Experiments show that if pore density of the filter element is less than 80 mesh, the fuel flow rate will drop from 120L/h to 70L/h, the pump body load will increase by 15%, which will lead to sudden pressure drop of 40% at idle operation. For example, in one maintenance case, a vehicle that had traveled 60,000 kilometers had a clogged filter (the measured flow rate was as low as 45L/h). The fuel pump operating current rose from 5A to 7.2A, eventually leading to a thermal fade effect, and the idle pressure dropped from 2.8bar to 1.5bar.
Circuit problems cannot be ignored either. The fuel pump is driven by a 12V voltage. If the resistance of the wiring harness is greater than 0.5Ω (nominal resistance must be ≤0.2Ω), motor power drops from 60W to 40W and directly affects the stability of fuel supply. One research institute statistics for 100 cases of standstill pressure faults show that 34% are due to voltage fluctuation, among which the range of pressure fluctuation caused by relay contact oxidation (contact resistance rises to 1.8Ω) is as high as ±1.2bar. Also, when the frequency deviation of the FPCM PWM signal exceeds 5%, the duty cycle adjustment accuracy is weaker, and thus the idle flow error rate can reach up to 20%.
The malfunction of the fuel pump pressure regulating valve can also cause problems. For example, the spring life of fatigue for a specific control valve is 100,000 opening and closing times. If it is subject to high temperature for long-term (fuel temperature > 80℃), its attenuation rate of elastic modulus is two times greater, thus making the set pressure drift to 2.2bar from 3.0bar. Industry testing shows that when the leakage of the regulating valve is more than 15mL/min, the system has to burn an additional 8% of the volume of the pump oil to compensate for the pressure, which again accelerates the wear on the pump body.
Finally, compatibility of the oil product is a significant factor. The hygroscopic nature of ethanol-blended fuel tends to raise the internal fuel pump housing humidity above 60%, accelerating metal component rusting (where rust layer thickness is > 0.1mm, the impeller clearance is increased by 50μm), and the volumetric efficiency is reduced by 12%. For instance, in the Brazilian market, due to the marketing of E27 ethanol gasoline, the failure rate of fuel pumps is 18% greater than that of traditional gasoline types. Of these, insufficient idle pressure accounts for 41% of the malfunction complaints. Through multi-dimensional data analysis, fuel pump degradation is typically the combined result of mechanical, electrical and chemical factors. There is a need to precisely identify the source of the fault by merging real-time diagnostic parameters (e.g., the fuel pressure sensor reading and pump current waveform).