Pre-injection function before installing the new Fuel Pump directly affects the fuel supply system start-up efficiency. According to the SAE J2719 standard, pre-injection of the fuel pump must increase the low-pressure fuel line pressure to 250-300 kPa within 10 seconds to avoid air lock from causing the fuel injector flow error > ±8%. For example, the BMW Technical Bulletin (SI B13 07 21) requires that while replacing the fuel pump of the N55 engine, the pre-injection program must be started three times using the ISTA diagnostic tool (every 5 seconds) in a way that oil pressure will be 280±15 kPa; otherwise, cold start failure rate will increase by 42%.
Pre-injection equipment selection has a major influence on the operating success rate. To operate a manual vacuum pump (e.g., Mityvac MV8000), one needs to pump 20-25 times within a minute of 90 seconds to achieve a vacuum level in the oil circuit below -70 kPa, while its fill-in rate by fuel will reach 98%. According to the North American Automobile Maintenance Association’s 2023 numbers, 37% of auto owners who failed to use the appropriate equipment doubled their initial ignition time out to 8-12 seconds (standard: 3 seconds) due to an absence of pre-injection and boosted battery energy consumption by 15%. Use. of electric pre-injection units (e.g., Schley 59050, cost $220) allows the process to be optimized to 30 seconds and the efficiency of the fuel line exhaust to be increased by 90%.
Ambient temperature is a significant factor in the preinjection effect. When the fuel temperature is below 10°C and the viscosity rises from 0.7 cSt to 1.5 cSt, the pre-injection time should be increased to 120 seconds and repeated twice. For instance, a report by the Norwegian Volvo Owners’ Club indicates that at a temperature condition of -5°C, 52% of vehicles which were prefilled with unheated fuel directly had oil pressure fluctuations in excess of ±50 kPa (the standard range of ±20 kPa), requiring a secondary fuel of 0.8 L. Application of fuel heating tapes (3°C/minute heating rate and 50W power) may increase pre-injection success rate from 58% up to 94%.
Pre-injection operation should be absolutely by the manufacturer torque specification. Torque tightening installation bolts of the fuel pump flange is usually 8-12 N·m (for example, on the Volkswagen MQB platform). Over-tightening to 15 N·m can cause the sealing ring to be compressed and decrease from the set value of 1.2 mm to 0.8 mm, increasing the probability of fuel leakage by 23%. According to NHTSA recall statistics, in 2020, there was a certain Japanese brand whose 0.7% of vehicles experienced fuel leakage (more than a rate of more than 5 drops per minute) after the fuel pump replacement due to the lack of clear torque value marking in the repair guide, resulting in one recall that cost $650.
The system check after the pre-injection of the Fuel Pump is of critical importance. The PID 0x0A of the fuel pressure sensor should be verified with the OBD-II tool to ensure that the median idle oil pressure is 350 kPa (fluctuation < 5%), and the maximum pressure during sudden acceleration is not less than 400 kPa. For instance, real tests by Ford F-150 owners proved that lower pre-injection operations would cause the fuel pump load current to rise from its normal level of 4.5A to 7.2A, increase the motor temperature rise rate by 3°C/minute, and decrease the lifespan by 40%. Employ Fluke 87V multimeter to determine the working current (error < ±0.2A) and supplement with a smoke leak detector (e.g., OTC 6520) to verify the sealing performance. The cost is $15 for one test, which can reduce the rework risk by 92%.
Industry practices recommend that the pre-injection process has to integrate mechanical exhaust (elimination of more than 90% of bubbles), electronic control (activating the pump body 2-3 times), and pressure checks (ongoing checking for 30 seconds). As per the ISO 16750-4 environmental test specification, in humid areas > 80% or high-altitude areas > 2000 meters, the pre-injection period needs to be prolonged by an extra 20%. For instance, Tesla Cybertruck’s maintenance manual particularly states that following the replacement of the fuel pump in high-altitude areas, the “High-altitude adaptation mode” should be activated through Toolbox 3.0 to increase 8% the target oil pressure value, otherwise, the fuel supply error will lead to a 12% power decrease of the motor.