The pressure requirements of the electronically controlled fuel injector constitute a hard threshold. The inlet oil pressure for the normal operation of the fuel injector needs to be stably maintained at 3.5-4.0Bar (for the gasoline direct injection system, it is even as high as 15-20Bar). The low-pressure fuel pump (with a standard output of 0.5-1.5Bar) is unable to drive the fuel injection valve to overcome the 12kgf spring preload, directly resulting in a flow deviation of over ±22%. When the measured fuel injection pulse width is 4ms, the actual fuel injection volume only reaches 55% of the theoretical value. The emission test data from the US EPA shows that when the oil pressure is lower than 3Bar, the fluctuation range of the time-space fuel ratio expands to ±14% (standard ±3%), the catalyst conversion efficiency drops by 28%, and the risk of excessive emissions increases by 9 times.
System compatibility issues triggered a chain of failures. The fuel rail’s fuel storage volume drops to 20ml under low pressure (the standard requirement is 50ml), and the probability of fuel supply interruption during sudden acceleration reaches 83%. In 2019, due to the recall incident of the mixed installation system of a certain German automaker, it was shown that the 1.8Bar low-pressure pump combined with the direct injection injector in the cylinder caused: ① The oil rail pressure sensor wrongly reported the fault code (the trigger rate of DTC P0193 was 91%); ② The wear rate of the plunger of the high-pressure pump increases by 300% due to dry friction. The sticking and jamming rate of the fuel injector needle valve has risen to 17%. The single maintenance cost exceeds 2000 (including 450 high-pressure pumps +$120 per ×4 fuel injectors).
The deterioration of atomization quality leads to economic losses. Under low-pressure conditions, the average diameter (SMD) of fuel injection soared from 15μm to 40μm, the droplet evaporation time was prolonged by 250%, and the soot generation in the combustion chamber increased by 45%. Bench tests have confirmed that when the oil pressure is 1.5Bar, the effective thermal efficiency of the engine decreases by 18% and the fuel consumption surges by 15%. In the case of North American users, the annual fuel cost of a 2.0T engine that switched to a low-pressure pump increased by $320 (calculated based on 20,000 miles), which is equivalent to 14 times the price difference of the pump body.
Circuit risks escalate simultaneously. The fuel injector solenoid valve needs to maintain a peak voltage drive of 65±5V. When insufficient oil pressure causes abnormal plunger stroke, the pulse width of the driving current extends from 2ms to 5ms, and the junction temperature of the ECU power transistor exceeds the failure threshold of 150℃. Statistics from a certain repair shop show that under such working conditions, the burnout rate of the engine control module (ECU) is as high as 33%, with associated losses exceeding $1,500. The Fuel Pump control module that supports 30kHz PWM modulation (such as DENSO 230-0001) must be used to maintain the stability of the system.
The cost-effectiveness of compliant alternative solutions is clear. The unit price of high-pressure fuel pumps conforming to ISO 22031 standard (such as Walbro F9000) is 90-150. The renovation cost includes 80 pressure regulating valves +60 wiring harnesses. Compared with the average annual excess operation and maintenance cost of 890 caused by the mismatching of low-pressure pumps, the payback period of investment is only 5.7 months. Volkswagen TSI Technical Bulletin particularly warns: The mixed use of low-pressure pumps will increase the probability of warranty expiration to 100%, and at the same time, there is a risk of an EPA fine of $47,500 per vehicle due to excessive emissions.