The core indicator of overheating of the Fuel Pump is that the temperature exceeds the design threshold (usually > 85℃). At this time, the insulation layer of the motor winding may carbonize (the resistance decreases by > 15%), resulting in an abnormal increase in current. According to the SAE J1349 standard test, the normal operating temperature should be 40-65℃. If the temperature rises above 75℃, the motor efficiency drops from 88% to 72%, and at the same time, the operating current increases from 8A to 11A (overloaded by 37.5%). The NHTSA case in the United States shows that after operating at a continuous high temperature (> 80℃) for 100 hours, the wear rate of the carbon brush accelerates to 0.02mm/ hour (normal 0.005mm), and the eccentricity of the impeller expands from 0.03mm to 0.12mm (ISO 1940 standard allows ≤0.05mm), causing a 28% attenuation in the flow rate.
Abnormal noise is a direct signal. When the temperature of the Fuel Pump is > 70℃, the viscosity of the bearing grease decreases from ISO VG 32 to VG 10, the friction coefficient increases from 0.05 to 0.15, and a high-frequency abnormal noise of 2-4kHz occurs (the decibel value increases from 50dB to 68dB). The actual measurement data of the Porsche 911 owner shows that at 2000rpm, the proportion of 3.2kHz components in the noise spectrum of the heat pump body increases from 5% to 22%, accompanied by a metal scraping sound of 3 to 5 times per second (the impeller contacts the pump cavity).
Fluctuations in fuel pressure reflect the risk of overheating. Under normal working conditions, the oil pressure fluctuation should be < ±0.3bar (ISO 15031-4). However, when overheated, due to the expansion of the sealing ring (the expansion rate of fluororubber increases from 2% to 5%), the standard deviation of the pressure fluctuation expands to ±0.8bar, and the trigger rate of the P0087 fault code recorded by the ECU increases to 63%. In the case of the Ford Ecoboost 2.3T engine, when the fuel pressure dropped from 4.0bar to 2.5bar, the fuel injection pulse width prolonged from 12ms to 18ms, the air-fuel ratio deteriorated from 14.7:1 to 17:1, resulting in the exhaust temperature rising to 980 ° C (normal 850 ° C).
The decrease in fuel flow is strongly correlated with temperature. When the temperature of the Fuel Pump rose from 50℃ to 80℃, the decrease in motor efficiency led to a flow rate reduction from 120L/h to 85L/h (a decrease of 29%). If the filter screens are clogged simultaneously (pressure difference > 1.5bar), the flow rate further drops to 60L/h, and the fuel vapor concentration (ppm) rises from 200 to 1200, triggering the risk of surface ignition (the probability increases by 12 times). Vehicle data from the Outback region of Australia shows that the traffic flow attenuation rate in high-temperature environments (> 40℃) is 38% higher than that in normal temperatures, and the overheating failure rate increases by 45%.
Abnormal electronic signals provide early warnings. The PWM drive signal of the Fuel Pump was detected using an oscilloscope. The normal duty cycle fluctuation should be < ±3% (such as 50%→49%→51%). When overheated, due to the change in winding resistance (such as dropping from 1.2Ω to 0.8Ω), the duty cycle jitter expands to ±8% (such as 50%→43%→57%), the ECU misjudges the load demand and wrongly increases the voltage to 14.5V (standard 13.5V±0.5V), accelerating the aging of the wiring harness (temperature rise rate 6℃/min vs. (Normal 2℃/min).
Physical deformation and leakage are ultimate manifestations. Continuous overheating (> 95℃) can lead to a mismatch in the thermal expansion coefficient of the plastic casing of the pump body (PA66-GF30 material expansion rate 0.8% vs. The metal parts accounted for 0.12%, the gap expanded to 0.3mm (allowable value < 0.1mm), and the fuel leakage rate soared from 0.05g/h to 2.1g/h (EPA Tier 3 limit of 0.05g/h). The disassembly case of the BMW N54 engine shows that the displacement of the impeller shaft sleeve of the heat pump body reached 0.15mm, the atomization Angle of fuel injection decreased from 80° to 55°, and the combustion efficiency in the cylinder dropped by 9%.
The environment and usage scenarios exacerbate risks. In desert areas (with a temperature > 45℃), vehicles have poor heat dissipation in the engine compartment. The temperature of the Fuel Pump is 15-20℃ higher than that in the normal environment, and the failure rate increases by 3.2 times. During the DPF regeneration cycle (exhaust temperature 600℃) of diesel vehicles, the heat radiation from the fuel return pipe causes an additional 8-10℃ increase in the pump body temperature. It is necessary to forcibly install a heat shield (such as DEI 010395, with a reflectivity > 90%) to reduce the heat load.
Economic warning: The maintenance cost of ignoring signs of overheating is 5 to 8 times that of preventive maintenance. For example, the cost of replacing the overheated damaged Fuel Pump assembly is 400, while cleaning the filter screen in advance (20) or upgrading the wiring harness ($85) can avoid 90% of overheating faults. NHTSA statistics show that timely intervention can reduce chain damage (such as damage to fuel injectors and high-pressure pumps) by 67%.