Fuel Filler Cap: Testing and Inspection

Fuel tank filler cap. Checking seal

Special tools:
999 5757 Filler cap tester 999 5757 Filler Cap Tester

Checking the sealing ring in the fuel tank filler cap




Check that the sealing ring (1) in the fuel tank filler cap is intact, is correctly positioned and has a clean mating surface.
The temperature of the fuel tank filler cap must be 20°C +/- 10°C (68°F +/- 18°F).
The leak test below checks the elasticity of the rubber and for cracks and material wear
Use tool 999 5757 Filler cap tester 999 5757 Filler Cap Tester for the seal test.

Checking hoses for the vacuum pump and fuel filler cap adapter




Check that the hoses for the vacuum pump and fuel filler cap adapter are securely installed.

Check the vacuum pump for leaks




Check the vacuum pump for leaks by blocking the hole in the adapter with a finger and pumping out the air. There should be no increase in pressure.
Repeat the above, this time with overpressure. There should be no reduction in pressure.

Installing the fuel filler cap




Install the fuel filler cap to the adapter. Turn until you hear a click

Leak test, vacuum




Set the selector to position VACUUM.
Slowly pump out the air to minus (-) 3 kPa. Wait until the vacuum has stabilized. Pressure increases of 1 kPa per 30 seconds are permitted.
Replace any fuel filler cap that fails this test.

Testing vacuum valve




Pump air out until the vacuum valve opens. This should occur between minus (-) 4 and minus (-) 12 kPa.

Leak test, pressure




Set the selector to position PRESSURE.
Slowly pump in the air to plus (+) 3 kPa. Wait until the pressure has stabilized. Pressure reductions of 1 kPa per 30 seconds are permitted.
Replace any fuel filler cap that fails this test.

Testing relief valve




Pump air in until the relief valve opens. This should occur between plus (+) 14 and plus (+) 30 kPa.