Worn Fuel pumps directly affect the stability of injection pressure. A study in the Journal of Internal Combustion Engine Engineering in 2023 shows that: When the output pressure of the oil pump is reduced from the standard 58.5 psi to 43 psi, the Soter mean diameter (SMD) of the atomized particles in the injector increases from 15μm to 28μm, and the evaporation time of the droplets is prolonged by 50%, resulting in the standard deviation of the oil-gas mixture inhomogeneity in the combustion chamber reaching 18%. The measured data from the Toyota Laboratory indicates that the pressure fluctuation of the aging oil pump is ±7 psi (exceeding the ±2 psi specified by ISO 14297), resulting in a 12% deviation of the injection cone Angle and a 9% loss of combustion efficiency.
The core cause is the wear of the oil pump impeller leading to flow attenuation. The Bosch technical manual points out that under 100,000 kilometers of working conditions, the impeller clearance increases by 0.2mm, the flow output attenuation rate is 17%, and the designed flow rate of 160 L/h drops to 133 L/h. When the engine is fully loaded at 6000 rpm, the actual rail pressure collapses from 58 psi to 41 psi. At this point, the ECU forcibly extends the fuel injection pulse width to 6.5ms (the normal value is 4.2ms), and the probability of the fuel droplet diameter exceeding 40μm increases by 83%. In the 2022 Ford 2.3T engine recall incident, due to the wear of the fuel pump, the fuel injection atomization was poor, and the cold start hydrocarbon emissions exceeded the standard by 320%.
The thermodynamic effect intensifies the atomization deterioration. SAE Paper 2024-01-0873 confirms that the efficiency of the wear oil pump decreases by another 15% in a high-temperature environment. When the fuel temperature reaches 50℃, the pressure of the weakened fuel pump drops from 45 psi to 32 psi, and the fuel viscosity decreases from 0.76cSt to 0.63cSt, resulting in a 40% reduction in the energy of nozzle jet breakage. Under the idle condition of 1500rpm, the proportion of atomized particles >50μm rises to 22%. Typical phenomena include the standard deviation of rotational speed fluctuation rising from ±5 rpm to ±25 rpm, and the voltage fluctuation of the exhaust gas oxygen sensor exceeding 0.4V.
Diagnosis and prevention require quantitative monitoring. The industry recommends testing the performance parameters of the oil pump every 50,000 kilometers: maintaining a rail pressure of 58±2 psi, with flow attenuation not exceeding 15% of the design value, and voltage fluctuation range of 11.5-14V. The recommended replacement cycle is 8 years or 120,000 kilometers. If the Delphi HFP-943 model oil pump is used, the stability of the spray penetration distance can be maintained within ±0.5mm, reducing the risk of incomplete combustion by 90%. NHTSA statistics show that the precisely matched Fuel Pump solution reduces the number of knock repair cases caused by poor atomization by 38%.