The compatibility differences of materials result in a simultaneous replacement necessity as high as 95%. When the modern Fuel Pump system uses alcohol-containing fuel, the dissolution and expansion rate of the inner wall of the common rubber oil pipe exceeds 15% (the volume expansion of NBR material reaches 18.5% after 90 days of contact with E15 gasoline), resulting in a contraction of the inner diameter of 0.8-1.2mm. Experimental data show that reducing the inner diameter from 7mm to 6.2mm can reduce the flow rate by 22%, forcing the working current of the oil pump to increase by 2.7A (an increase of 40%). The SAE J30R9 standard in the United States stipulates that fuel pipelines must withstand a continuous high temperature of ≥85℃. However, the upper limit of the temperature resistance of vehicle fuel pipelines manufactured before 2010 was only 70℃, and the aging rate increased by 300% in turbocharged models.
The pressure adaptation requirements determine the upgrade scope. The working pressure of the direct injection system in the cylinder exceeds 350bar (the traditional pipeline can only withstand 5bar), and the corresponding burst strength of the PTFE-lined steel pipe needs to reach 3000psi (the ordinary nylon pipe is only 400psi). The technical notice of the BMW B48 engine states that if the pipeline from the high-pressure oil pump outlet to the oil rail section is not replaced simultaneously, micro-cracks are likely to occur after 30,000 start-stop cycles, causing a leakage of 0.2L/min (more than 75 times the allowable value stipulated by environmental protection regulations). What is more serious is that the pressure fluctuation increases to ±12bar (the standard value is ±1.5bar), directly leading to a 4.3% decrease in combustion efficiency.
The risk of interface corrosion collaboratively enhances the failure rate. When the outlet joint of the aluminum alloy oil pump comes into contact with the new and old oil pipes, the electrochemical corrosion rate difference reaches 0.15mm per year. After-sales data of Ford F-150 shows that when the old oil pipe left after the oil pump is replaced alone, the failure rate of fuel leakage caused by pitting corrosion of the sealing surface reaches 37% (only 1.2% in the combined replacement group). This problem is more pronounced in coastal areas with high salt fog, where the corrosion rate is as high as eight times that of inland areas, resulting in a reduction of the seal failure cycle from 10 years to 1.8 years.
There is a concealed interlocking effect in the aging working conditions. The accumulation of stripped substances on the inner wall of the fuel pipeline of an 8-year-old vehicle exceeded 0.8g/ m (including gel particles with diameters of 20-50μm), and the filter screen was contaminated by 35% within 96 hours after the new Fuel Pump was replaced. General Motors laboratory simulations have proved that such contamination causes the pump flow rate to decline by 28% after 500 hours of operation, while accelerating motor wear by 120%. If the old pipeline is retained, the incidence of loosening of the connecting parts caused by the decrease of its elastic modulus increases by 67%, and the probability of oil pipe disconnection in the vibration test reaches 2.1 times per thousand hours.
The comprehensive cost model supports collaborative replacement. Take the Volkswagen MQB platform as an example: The cost of a single oil pump replacement is ￥1,200 + labor cost is ￥300. The joint replacement plan increases the oil pipe material cost by ￥480, but saves ￥420 in the time for secondary disassembly and assembly (the maintenance time is reduced from 3.5 hours to 2 hours). The insurance claim database shows that the secondary repair rate due to the retention of old oil pipes is as high as 19%, and the additional cost per time is approximately 1,500 yuan. The full life cycle calculation proves that the joint replacement strategy can reduce the total holding cost by 31% and simultaneously reduce the risk of fuel vapor emission accidents by 87%.