Evaporative Emissions System: Testing and Inspection

Fig. 65 Slack Tube Tester:

Special Tool Required:
Slack tube pressure tester (US 4487), Fig. 65.
Hand operated air pump (a bicycle pump or similar).

Warning!
These tests involve the use of equipment that contain mercury. Mercury is a toxic and hazardous material. Exercise care when handling.
Do not allow mercury to come in contact with eyes, nose, skin, etc.
When equipment is not in use, store carefully in a properly designated area.
Be sure both valves are closed when storing tester.

Before testing, check;
Fuel filler cap securely closed.
To prevent the need for excessive pumping to pressurize the system, the fuel tank should be at least 2/3 full.

1. Disconnect the small hose from the charcoal canister.
2. Holding the slack tube tester (tool US 4487 or equivalent) vertically, connect it to the disconnected hose from the charcoal canister.
3. Open both slack tube valves 1/2 turn.
4. Move the scale on the tester so that the zero line is even with the tops of the mercury columns.
5. Pressurize the fuel system to 1.3 inches of mercury (in. Hg) using a hand pump.
NOTE, If the system reaches 1.3 in. Hg soon after you begin pumping, there is reason to suspect that the gravity valve (located above the fuel tank) or the hoses to it, might be pinched or blocked. Even with the fuel tank 2/3 full, it should take a considerable time to pressurize the fuel system.
a. After reaching 1.3 in. Hg on the scale, wait 5 minutes. Pressure should not drop below 1.2 in. Hg.
b. If the pressure drops below 1.2 in. Hg, check the fuel filler cap for leaks with a soap and water solution, and repair or replace as necessary.
6. Pressurize the system to 1.3 in. Hg, and wait 5 minutes.
If the pressure drops below 1.2 in Hg, disconnect the hose from the top of the gravity valve (between the gravity valve and the charcoal canister) and plug the hose.
7. Pressurize the system to 1.3 in. Hg, and wait 5 minutes.
a. If the pressure drops below 1.2 in. Hg, the leak is between the gravity valve and the charcoal canister.
b. If the pressure does not drop below 1.2 in. Hg, reconnect the gravity valve and re-pressurize the system.
8. Check the hoses and connections at the expansion tanks and fuel tank using a soap and water solution. Repair leaks as necessary.
9. After all leaks are repaired, repeat test to verify that all leaks are fixed.
10. After all tests are completed, close both valves on the slack tube tester, and store properly.