Fuel Filler Cap: Testing and Inspection

Special Tools
999 5757

Checking fuel cap sealing ring
The temperature of the filler cap should be 20°C ± 10°C (68°F ± 18°F).
Tool 999 5757 must be used for the leakage test.





Check seal for any damage. Replace cap if necessary.
Check seating surface for the seal on the fuel cap so that no cuts or nicks are present. Replace fuel cap if necessary.
Check seating surface for seal on the filler neck so that no cuts or nicks are present.

Checking hose to the vacuum pump and fuel cap adapter





Check so that hose on the vacuum pump and the fuel cap adapter is correctly installed.

Checking seal vacuum pump





Check vacuum pump seal by blocking the hole in the adapter with i.e. your finger and pump out the air. There must be no increase in pressure.

Installing the fuel cap





Fit the fuel cap on the adapter. Turn until you hear a click/ratcheting.

Leakage test, vacuum





Move the selector knob to the VACUUM position.
Slowly pump out the air to negative (-) 3 kPa (0.4 psi).
Wait until the vacuum has stabilized. A pressure increase of 1 kPa (0.2 psi) every 30 seconds is permissible.
If fuel cap fails the test it must be replaced.

Testing vacuum relief valve





Pump out the air until the low pressure valve opens. This should occur between negative (-) 4kPa (0.6 psi) and negative (-) 12 kPa (1.7 psi).

Leakage test, pressure





Move the selector knob to the PRESSURE position.
Slowly pump in the air to positive pressure of (+) 3 kPa (0.4 psi). Wait until the pressure has stabilized. A pressure decrease of 1 kPa (0.2 psi) every 30 seconds is permissible.
If fuel cap fails the test it must be replaced.

Testing the relief valve





Pump in air until the pressure relief valve opens. This should occur between positive pressure of (+) 14 kPa (2.0 psi) and positive pressure of (+) 30 kPa (4.0 psi).