Bowl Vent Valve: Testing and Inspection

Fig. 77 Checking Vacuum To The Air Vent Cut-Off Diaphragm:

1. Disconnect the hose at the air vent cut-off diaphragm and install a vacuum pump to the hose, Fig. 77.
2. Apply vacuum to the cut-off diaphragm.
a. With the ignition switched OFF, the cut-off diaphragm should not hold vacuum.
b. With the ignition ON, the cut-off diaphragm should hold vacuum.

Fig. 78 Checking Voltage At Vacuum Holding Solenoid:

3. If the cut-off diaphragm does not hold vacuum with the ignition ON;
a. Check the hoses for cracks or faulty connections.
b. Check for voltage at the vacuum holding solenoid, Fig. 78.
c. If there is voltage, replace the vacuum holding solenoid and re-test.
d. If there is no voltage, check for an open circuit in the black/yellow wire between the vacuum control box connector and the #1 (15 A) fuse in the fuse box.
4. Start the engine and check for vacuum at idle. Vacuum should be available. If vacuum is not available;
a. Check hose routing.
b. Check hoses for cracks or bad connections.
c. Check for blockages in the vacuum line.
d. If no faults are found, replace the vacuum holding solenoid valve and re-test.
5. Turn the ignition OFF. The vacuum should drop to zero.

Fig. 79 Applying Vacuum To Air Vent Cut-Off Diaphragm:

6. Disconnect the vacuum pump from the vacuum holding solenoid valve hose and connect it to the air vent cut-off diaphragm, Fig. 79, and apply vacuum. Vacuum should remain steady.
a. If vacuum remains stable, the diaphragm is OK.
b. If the vacuum drops, replace the diaphragm and re-test.
7. Remove the vacuum pump and reconnect all hoses after completing tests.