The common causes of unstable idle speed of the Fuel Pump are voltage fluctuations and mechanical wear. According to the test data of SAE International, when the vehicle is idling, the output voltage of the generator may drop from 14.2V to 12.8V (fluctuation ±5%), resulting in an 8%-12% decrease in the rotational speed of the Fuel Pump motor. The fuel pressure dropped from 58 psi to 48 psi (lower than the minimum value of 50 psi set by the ECU). Take the recall incident of the Honda Accord in 2022 as an example. The duty cycle of the PWM signal of its Fuel Pump control module (FPCU) fluctuated from 75%-85% to 60%-95% at idle speed, causing the fuel flow error rate to increase from ±2% to ±7%, and the idle speed fluctuation reached ±50 rpm (the normal value was ±10 rpm).
Mechanical wear directly affects the stability of flow. Research from Bosch Laboratory shows that when the wear of the Fuel Pump impeller exceeds 0.1 millimeters, the flow attenuation rate increases from 3% to 9%, and the pressure fluctuation range under idle conditions expands from ±1.5 psi to ±4 psi. Statistics from a certain maintenance platform show that among vehicles with a mileage of over 80,000 kilometers, 32% of Fuel pumps have motor current increase from 4A to 6A due to wear of bearing balls (with a diameter reduction of 0.05 millimeters), winding temperature peak reaches 95°C (exceeding the design limit by 20%), and the probability of idle fuel supply interruption increases to 18%. In addition, carbon brush wear (length < 5 millimeters) will increase the electrical contact resistance by 0.2Ω, reduce the motor efficiency by 15%, and cause periodic unstable fuel supply (fluctuation frequency 2-5 Hz).
Pollution of the fuel system aggravates the idle problem. The report of the American Automobile Association (AAA) indicates that when using Fuel containing impurities (particle size > 50 microns), the clogging rate of the Fuel Pump filter increases by 40%, the idle flow rate drops from the designed value of 2.5 L/min to 1.8 L/min, and the ECU is forced to extend the fuel injection pulse width to 12 ms (the normal value is 8 ms). This led to the deviation rate of the air-fuel ratio expanding from ±3% to ±9%. Take the Volkswagen EA888 engine as an example. Water vapor condensation in the Fuel tank (humidity > 15%) will cause the surface corrosion roughness (Ra value) of the Fuel Pump impeller to increase from 0.8 microns to 3.2 microns, the cavitation probability to rise from 2% to 12%, and the idle pressure pulsation amplitude to reach ±6 psi (safety threshold ±2 psi).
Intelligent regulation technology can significantly improve stability. The Dynamic Fuel Pump module (DFPM) launched by Delphi monitors the fuel pressure in real time (with a sampling rate of 1000 Hz), increases the PWM frequency from 300 Hz to 1000 Hz at idle speed, and compresses the standard deviation of flow fluctuation from 0.5 L/min to 0.1 L/min. When the integrated Fuel Pump of Tesla Model 3 detects voltage fluctuations, it automatically activates the supercapacitor buffer (with a capacity of 500F), reducing the current fluctuation amplitude from ±1.2A to ±0.3A and improving the idle pressure stability by 40%. Data from Frost & Sullivan shows that in 2023, the idle failure rate of models equipped with adaptive control Fuel pumps decreased by 55%, maintenance costs reduced by 30%, and idle fuel economy improved by 5%-8%.