Insufficient Fuel supply is one of the main culprits for engine acceleration jerks, and the core lies in the fact that the Fuel Pump cannot maintain precise flow control. When the throttle opening suddenly increases from 15% to 85% within 0.3 seconds, the engine’s fuel demand instantly rises by 300%, and the flow response delay of the aging fuel pump exceeds 100 milliseconds. Bosch laboratory tests show that: When the pressure fluctuation range exceeds ±12% (for instance, when the standard value drops from 350kPa to 308kPa), the air-fuel ratio will instantaneously dilute to 16.8:1. At this point, the ECU is forced to reduce the ignition advance Angle by 7-10 degrees, resulting in an 18% decrease in torque output during the 20-50km/h acceleration range. Specifically, when the accelerator pedal is pressed down by 40%, the vehicle speed response is delayed by 0.8 seconds.
The electrical degradation of the Fuel Pump causes periodic jerks. The wear of the motor commutator causes the winding current fluctuation rate to exceed ±15% (normal value < 5%), resulting in pressure pulsations of 4 to 6 times per minute. Audi’s TSB technical announcement disclosed that the 2.0TFSI engine, which has traveled 120,000 kilometers, experienced a peak and valley difference in oil pressure of 42kPa (within the allowable range of ±8kPa) during constant cruising at 2000rpm due to this kind of fault, resulting in 3.2 brief fuel outages per kilometer. Road measurements on ADAC roads in Germany show that under such conditions, when a vehicle travels at a constant speed of 80km/h, the acceleration fluctuation reaches ±0.3m/s², and passengers’ perception of unevenness increases by 5.7 times.
Clogging of the filtration system creates an accelerated trap. When the clogging area of the filter screen exceeds 40%, the fuel flow rate decays by 35% during rapid acceleration. The fault analysis of Chrysler’s recall of 2.3 million vehicles in 2019 confirmed that when the throttle is full, the peak pressure difference at both ends of the clogged filter screen reaches 550kPa (the rated limit is 380kPa), and at this time, the fuel injection pulse width needs to be increased from 2.8ms to 4.2ms to compensate. This delay increases the acceleration time from 0 to 100km/h by 1.5 seconds, and 80% of the jerks occur in the speed range of 40 to 70km/h, especially on uphill sections where the ECU records a fire rate of up to 1.5 times per kilometer.
Ethanol fuel accelerates performance deterioration. Gasoline containing 15% ethanol will increase the swelling rate of the fuel pump impeller by 200%, causing the axial clearance to decrease from 0.12mm to 0.05mm. Experimental data from the Brazilian Energy Research Institute shows that after using E15 gasoline for 60,000 kilometers, the maximum flow rate of the fuel pump dropped from 310L/h to 228L/h (-26.5%). When driving at a constant speed of 60km/h, the fluctuation range of the ECU fuel correction value reached ±28%, and there were 17.3 perceptible jutters per 100 kilometers. Compared with ordinary gasoline users, ethanol gasoline car owners have a 220% higher probability of complaining about poor acceleration.
Unstable voltage supply induces random faults. When the impedance of the wiring harness is greater than 0.8Ω (the standard value is 0.2Ω), the working voltage of the fuel pump drops below 10V. Nissan’s maintenance database shows that for such faults, the oil pressure recovery time is extended to 2.4 seconds (the standard is 0.8 seconds) at the moment of idle start-stop and restart, resulting in 23% of vehicles experiencing power interruption 3 seconds before the green light starts. Tests conducted by CAFE in the United States show that such defects increase fuel consumption in urban conditions by 11%, with an average annual additional fuel cost of 2,400 yuan.
The system solution requires precise diagnosis:
Dynamic oil pressure test: Pressure fluctuation at full throttle is less than ±5% (for example, Toyota requires 380kPa±19kPa)
Flow calibration: Idle flow > 90L/h, full-load flow > 180L/h
Current monitoring: Working current fluctuation < ±0.5A (at 12V voltage)
Volvo’s after-sales data confirms that after replacing the fuel pump according to the standard, the complaint rate of engine jerking dropped by 92%, while urban fuel consumption decreased by 9.7%. The payback period for comprehensive maintenance investment is only 4.8 months. Especially for models equipped with direct injection technology, preventive replacement extends the lifespan of high-pressure fuel pumps by 47%, effectively avoiding the average fuel system overhaul cost of ￥6,800.