After disassembling and repairing the fuel injector, strict sealing testing is required to ensure no fuel leakage or abnormal pressure. The following are the specific methods and operating points:
1、 Preparation before testing
Tools and equipment:
Fuel injection test bench (or self-made simple pressurization device)
Pressure gauge (accuracy ≥ 0.1MPa), connecting oil pipe, joint adapter
Beaker/transparent container, cloth, fuel (compatible with injector model)
Installation inspection:
Confirm that the fuel injector assembly is installed correctly, the sealing ring is not twisted or misaligned, and the tightening torque of the joint meets the standard (such as Bosch fuel injectors, which are usually 8-12N · m).
2、 Sealing test method
1. Static sealing test (detecting low-pressure leaks)
Operation steps:
Connect the fuel injector to the test bench and keep it inactive (with the solenoid valve powered off).
Slowly increase the pressure to the idle pressure of the system (such as about 3-5 bar for gasoline cars and 30-50 bar for common rail systems in diesel cars).
Turn off the pressure source, observe the decrease of the pressure gauge, and at the same time, use a beaker to collect the leaked fuel under the fuel injector.
Qualification criteria:
The pressure drop within 1 minute is ≤ 0.5 bar (slightly different models, refer to the original factory manual).
There is no obvious dripping at the fuel injector (≤ 1 drop per minute is normal, and ≤ 0.5 drops are required for diesel high-pressure fuel injectors).
2. Dynamic sealing test (simulating working conditions)
Operation steps:
Raise the pressure to the rated working pressure (such as 150-200 bar for gasoline direct injection systems and 1600-2000 bar for diesel common rail systems).
Trigger the injector pulse signal (frequency 1-2Hz, duration 5-10ms) to intermittently inject fuel.
After stopping fuel injection, observe the pressure holding ability and the sealing condition of the fuel injector.
Qualification criteria:
After stopping fuel injection, the pressure drops by ≤ 5% of the rated pressure within 10 seconds.
The fuel injector has no fuel leakage during the non injection stage, and the atomization is uniform, without deviation or droplet like oil particles during injection.
3. Negative pressure test (optional, detecting minor leaks)
Operation steps:
Apply negative pressure of * * -0.1MPa * * inside the fuel injector (achieved through a vacuum pump) for 30 seconds, and observe whether there are bubbles overflowing from the sealed part (applicable to precision fuel injectors such as diesel common rail nozzles).
Qualification criteria: No bubbles generated or ≤ 1 bubble per minute.
3、 Common leakage points and troubleshooting
Leakage on the sealing surface of the fuel injector nozzle
Reason: Scratching the nozzle needle valve seat, needle valve wear, or carbon residue during cleaning.
Solution: Use grinding paste to gently grind the needle valve and valve seat (non professionals recommend replacing the fuel injector assembly).
Leakage of joints or sealing rings
Reason: The sealing ring is twisted during installation, the joint is not tightened, or the material is aging.
Solution: Reinstall the sealing ring, tighten the joint to the specified torque, and replace the high-pressure resistant sealing ring (such as fluororubber material) if necessary.
Leakage of solenoid valve body
Reason: Wear of valve core seals and aging of electromagnetic coils result in loose closure.
Solution: Replace the internal sealing components of the solenoid valve or replace the solenoid valve as a whole.
4、 Precautions
Safe operation:
Wear protective goggles during high-voltage testing, keep away from the direction of fuel injection nozzle to prevent fuel injection from injuring people.
When using diesel for testing, attention should be paid to ventilation to avoid the accumulation of oil and gas.
Parameter calibration:
The test pressure must be strictly set according to the original factory technical parameters (such as Toyota injector rated pressure of 3.8 bar, Mercedes Benz common rail system of 1600 bar). Excessive pressure may damage components, while insufficient pressure cannot detect real leaks.
Multiple verifications:
Repeat the test 2-3 times to eliminate accidental factors (such as pressure fluctuations caused by incomplete air discharge in the pipeline during the first test).
Summary: Sealing testing is a key step in the maintenance of fuel injectors, which requires comprehensive evaluation through static and dynamic pressure testing, with a focus on pressure retention ability and nozzle leakage. If the self testing conditions are limited, it is recommended to use professional diagnostic equipment (such as car fault diagnosis instrument+fuel pressure gauge) or entrust a maintenance agency to ensure that the performance meets the standards after repair.
