Upgrading the Fuel Pump with excessive specifications may lead to a decline in fuel economy due to oversaturation of fuel supply. The core contradiction lies in the effective working range of the pressure regulation mechanism of the fuel system. The test report of the US Environmental Protection Agency (EPA) shows that when the maximum flow rate of the pump body exceeds the peak demand of the engine by more than 50% (for example, equiping a 300-horsepower engine with a pump with a flow rate of 450 L/h), it will cause more than 23% of the excess fuel to circulate through the return valve, consuming an additional 135W of power (equivalent to increasing the overall electrical load of the vehicle by 11.7%). In its analysis of the modification market in 2021, Bosch’s automotive division pointed out that fuel pumps with an 80% excessive flow rate on average increased urban fuel consumption by 1.8L/100km (approximately reducing MPG by 12.3%).
The failure of pressure regulation is a key node for the deterioration of energy consumption. When the original fuel rail pressure sensor (usually designed with a range of 4-6 bar) encounters a continuous pressure of more than 7 bar, the fuel pressure regulating valve (FPR) is forced to maintain an opening of more than 70% for pressure reduction. This state raised the temperature of the return oil pipe above 65℃ (the normal value is 48±5℃), and the heat radiation loss was converted into a fuel consumption growth rate of 2.4%. Daimler engineers confirmed in the SAE paper 2022-01-04.76 that if the pressure exceeds the calibrated value by 1.2 bar for more than 20 seconds, the stroke resistance of the high-pressure pump plunger will increase by 18%, resulting in an additional mechanical loss of approximately 0.8 horsepower on the crankshaft.
The deviation of system matching degree causes compensatory fuel consumption of the electronic control strategy. When the electronic control unit (ECU) detects that the air-fuel ratio deviates from the target value by ±5% (due to excessive fuel supply causing the oxygen sensor voltage to remain above 0.75V continuously), it will actively increase the ignition advance Angle by 3-8 degrees and reduce the fuel injection pulse width by 15% for correction. This dynamic adjustment caused the standard deviation of fuel consumption fluctuation to reach 0.41L in the NEDC test cycle, which was significantly higher than 0.17L of the original factory system. Track test data from the Toyota Gazoo Racing department shows that the upgraded fuel pump without recalibrating the ECU increased the combined fuel consumption of the GR Yaris by 14.7% (reduced from the original 33MPG to 28.1MPG).
Scientific selection can avoid the risk of energy efficiency loss. The flow calculation formula is: maximum horsepower of the engine ×0.018 (in gallons per hour). By choosing the pump body specification, the flow redundancy can be controlled within a reasonable range of 15%. The installation of an electronic pressure regulating valve (such as a PWM control system) can narrow the pressure fluctuation range from ±0.8 bar to ±0.2 bar, and keep the increase in fuel consumption within 1.9%. The case shows that after the owner of the Ford Mustang GT replaced the 255 L/h flow fuel pump (the original 190 L/h) and adjusted it with a professional ECU, the fuel efficiency on the highway was still maintained at 28MPG (only 0.7MPG lower than the original value), and the performance was improved by 24 horsepower while maintaining 92% of the fuel economy.