It requires the coordination between mechanical equipment and electronic diagnostic devices to check the pressure of the Fuel Pump. According to the SAE J2719 standard, the fuel pump operating pressure range in the gasoline direct injection system is 300-650 kPa, and the deviation should be less than ±5%. Use a mechanical fuel pressure gauge (such as Actron CP7838, with a range of 0-1000 kPa and an accuracy of ±1.5%) to connect to the oil rail test port. The pressure at idle speed should be stable at 350±20 kPa, and the peak pressure during sudden acceleration should not be lower than 420 kPa. For example, the 2022 Toyota Technical Bulletin (T-SB-0043-22) stated that when the pressure deviation exceeds ±30 kPa, it will trigger the fault code P0087, and the repair success rate is as high as 92%.
Electronic diagnostic equipment can monitor dynamic pressure curves in real time. Fuel pressure sensor PID 0x0A (normal range 0-1000 kPa) is read through the OBD-II interface. The median value of the data flow of the normal idle speed is 350 kPa, and the fluctuation rate is < 3%. If the pressure value at 2000 rpm is below 300 kPa or above 700 kPa, the fuel pump flow rate can be reduced by more than 15% or the pressure regulating valve has a problem. It is claimed in Bosch’s technical report that the “Fuel System Pressure Test mode” of KTS 560 diagnostic equipment (cost $2,300) can complete the 0-100% load pressure response test in 5 seconds with an accuracy of ±0.5%, and the misjudgment rate is 68% lower than the conventional method.
Ambient temperature significantly affects the test result. When the fuel pump starts at a low temperature of -20°C, the initial pressure needs to be as much as 250 kPa within 3 seconds (SAE Cold Start specification). If delayed to 5 seconds, the fuel atomization particle size will increase from 50 μm to 110 μm, and combustion efficiency will be decreased by 18%. For example, the owner of an Audi Q7 experimented in -15°C temperature and found that the original factory fuel pump (part number 06E127025G) pressure was only 220 kPa. When replaced with the VDO FP-7-1-003 pump having an integral heating function, pressure went up to 320 kPa, and the cold start-up time was lowered from 7 seconds to 2.3 seconds.
The test should take into account the condition of the fuel filter. When the filter pressure drop is greater than 70 kPa (normal < 20 kPa), the outlet pressure of the fuel pump will drop from the normal 400 kPa to 330 kPa, and the flow rate will be diminished by 22%. According to NHTSA’s recall data in 2023, a Korean brand contained a design problem in the fuel filter (80 PPI pore density, whereas the industry requirement is 120 PPI) that resulted in the fuel pump test pressure pass rate being as low as 54%. The pressure stability was increased to 98% following recall and replacement, and the unit cost of repair was $650.
Pressure test of the Fuel Pump needs thorough static and dynamic testing:
Static test: The pressure should be held at > 250 kPa for 5 minutes after the engine is shut off (if it leaks to < 150 kPa, check the sealing performance of the check valve).
Dynamic test: Measure the fuel pump current waveform with an oscilloscope (e.g., Picoscope 4425). The normal load current is 4-7A. If the peak current is > 9A and the frequency of fluctuation is > 200Hz, then the impeller may be stuck.
Comparative analysis: As per the ISO 16750-4 standard, if the reading of the pressure sensor and the mechanical gauge reading differ by more than ±20 kPa, the sensor needs to be calibrated first.
The case shows that after the owner of the Ford F-150 reprogrammed the fuel pump control module (FPCM) parameters with the FORScan software, the pressure fluctuation rate decreased from ±8% to ±2%, and fuel efficiency increased by 5%. The 2022 report of J.D. Power stated that among the fuel pump replacement operations which were not tested sufficiently, 32% of the vehicles had 40% of the lifespan of their fuel injectors decreased due to pressure imbalance, and the average yearly maintenance cost increased by $420.