The direct manifestation of fuel system venting failure is an engine start-up delay of more than 7 seconds or an increase of 60% in operating volatility. The main reason is that the residual air in the high-pressure pipeline reduces the continuity of the medium. The physical model shows that a 5-milliliter gas mass in an 8-millimeter diameter oil pipe can block the continuous oil supply for more than 12 seconds. Detailed in BMW Technical Notice SIB 13 02 19: The average time for the first start-up of an undrained N20 engine is 14.3 seconds (the standard value is 3 seconds), and the time for establishing Fuel pressure is prolonged to 800 milliseconds (normal < 300 milliseconds). The fundamental reason lies in that after replacing the Fuel Pump, the volume of air accounts for more than 15% of the pipeline capacity.
To perform forced venting, the oil pump’s pre-supply oil circulation needs to be activated three times (each time lasting 8-10 seconds), and it should be operated in conjunction with the dedicated exhaust pipeline release valve. By connecting the IDS diagnostic device to activate the oil pump control module, it was measured that during the pre-oil supply period, the flow rate needs to reach 1.8 liters per minute (corresponding to a pressure of 3.0 bar) in order to effectively expel the gas. The Volkswagen TSB 2045893 specification requires the installation of a transparent drain hose (with an inner diameter of 6mm) at the low-pressure end. It is considered qualified when the fuel bubble content flowing out is less than 0.5 milliliters per liter (visually no continuous bubbles for 3 seconds). In actual cases, the first start time of the 2019 Chevrolet Silverado was reduced from 11 seconds to 3.2 seconds under standard operation.
The key execution point lies in the operation of the fuel rail pressure relief valve. For the direct injection system in the cylinder (such as the Toyota D-4S), the high-pressure fuel rail bolts need to be loosened by 1.25 turns until the fuel flows out in a continuous column shape (flow rate > 150 milliliters/minute). The Mercedes-Benz WIS document stipulates that the engine should be started in a depressivented state for 10 seconds to expel microscopic bubbles (with a size < 50 microns) from the 300-bar high-pressure system. This operation can reduce the abnormal noise rate of the high-pressure oil pump by 73%. Actual measurements show that after the standard emptying, the pressure fluctuation range of the oil rail Narrows to ±20 bar (±50 bar in the initial state).
The later verification needs to be combined with data monitoring and dynamic testing. The oil pressure was detected using a Pico oscilloscope to establish a curve. The healthy system should rise from 0 to the target pressure within 400 milliseconds (deviation < 10%). During the road test stage, the Lambda value is monitored. Incomplete venting will cause the air-fuel ratio to fluctuate by more than ±0.8 (normal ±0.3) at a load of 1500rpm. Statistics show that maintenance operations that carry out a complete venting process (taking approximately 45 minutes) can reduce the rework rate by 68% compared to careless operations, and at the same time prevent the risk of coking in fuel injectors due to abnormal oil-gas mixture (shortening the expected lifespan by 42%).