The core indicator is that the start-up pressure establishment time exceeds the standard. A normal Fuel Pump should establish a pressure of 300kPa within 0.8 seconds after the ignition signal is connected, while an aging pump body requires more than 3.5 seconds. Tests conducted by Bosch Laboratory in 2023 show that when the pressure build-up time is greater than 2 seconds, the probability of the first ignition failure reaches 74% (18% under normal conditions), and the number of crankshaft rotations increases from an average of 4 to 9. At -10℃, this delay will cause the battery discharge to exceed 120Ah (the design limit is 100Ah), reducing the starter’s lifespan by 67%.
The decline in residual pressure maintenance capacity leads to system defects. A healthy fuel system should maintain a pressure of over 200kPa for 60 minutes after being turned off, while the failure of the check valve of the worn pump will cause the pressure to drop to zero within 30 minutes. The Mercedes-Benz technical bulletin states that when the residual pressure value is less than 80kPa, an additional 3 seconds are required to establish oil pressure during a hot start, and the air-fuel ratio is instantaneously diluted to 20:1 (the ideal value is 14.7:1). The engine maintenance data of BMW N52 shows that the probability of triggering the fault code P0171 in this state increases by 11 times, and each hot start consumes an additional 12ml of fuel (annual loss ¥580).
Loss of flow accuracy leads to out-of-control concentration. When the Fuel Pump impeller wears by 0.15mm, the idle flow rate decays from 40L/h to 28L/h, and the ECU is forced to increase the fuel injection pulse width from 2.5ms to 4.0ms. Ford’s 2022 recall case confirmed that the output of the aging pump was unstable at low speeds, and the variance of the mixture concentration fluctuation during cold starts reached ±1.8AFR (allowing ±0.5AFR), causing the ignition success rate to drop from 98% to 33%. At this point, the corrosion rate of the spark plug electrode increases by 220%, and for each failed startup, the carbon deposit increases by 0.03mm.
The attenuation of electrical performance forms a vicious circle. When the brush wears down to 1.0mm (3.2mm for new models), the working current fluctuates by ±15A (±0.8A for normal models), and the voltage drops below 9V. General Motors’ actual test: When starting at low temperatures, the voltage drop triggers the overload protection of the fuel pump control module (FPCM) of the ECU, forcibly cutting off the power supply for 200ms. This results in the first start success rate of the Nissan QR25DE engine being only 41%, requiring three attempts to start, with an 8-minute interval between each attempt for the battery to recover (the risk of waiting outside the vehicle in winter increases by 300%).
The Vapor Lock phenomenon is significant in the hot car scenario. When the cooling system fails, the oil pump temperature exceeds 110℃, causing the fuel gasification rate to rise to 15%. The SAE research report indicates that when gasoline vapor occupies 50% of the oil passage volume, the pump output efficiency drops by 83%. User data statistics of Honda 1.5L Earth Dream Engine: In the difficult events of hot car restart in summer, 76% were due to poor heat dissipation of the Fuel Pump. At this time, the fuel rail pressure was only 85kPa (required 250kPa), and the ECU recorded the frequency of the “System Too Lean” fault code as times/start.
The priority of diagnosis must be clear:
The first pressure establishment time: If it exceeds 1.5 seconds, it is abnormal
Residual pressure value at 15 minutes: If it is less than 150 kpa, replacement is required
Idle current fluctuation: > ±3A indicates brush failure
Hyundai Kia’s maintenance data shows that for Fuel pumps that meet either of the two standards, the probability of complete failure within 120 days is 91%. Timely replacement can prevent an average of ¥7,200 of associated damage (such as catalytic converter sintering and starter burnout), and restore the cold start success rate to 99.2% of the design value – which is crucial for driving safety in -30℃ cold regions and can reduce the risk of frostbite caused by waiting for rescue on the roadside by 98%.