The purge control valve is kept closed during idling in order to prevent vaporized fuel from entering into the intake manifold. This ensures positive control of high idle CO emission, which is a particular problem under high ambient temperatures. On feedback carburetor engines, the valve is opened when vacuum working on the diaphragm exceeds the preset value. On fuel injected vehicles, the purge system is controlled electronically.
See Figure 1Feedback Carburetor
- Remove the purge control valve from the vehicle.
- Connect a hand vacuum pump to the purge control valve nipple and apply a vacuum of 1.4 in. Hg to the valve.
- Blow air into the canister side nipple and make sure the air exits through the intake manifold nipple with vacuum applied.
- Replace the valve if defective.
- Disconnect the vacuum hose (red and black striped) from the purge solenoid valve.
- Disconnect the electrical terminal harness connector from the valve.
- Connect the vacuum pump to the nipple on the valve from which the red and black striped hose was disconnected.
- Connect the 12 volt power source to the valve terminals.
- Apply vacuum to the valve with the vacuum pump and alternately apply and remove battery voltage at the valve terminals. When battery voltage is applied, vacuum should be released from the valve. When voltage is removed, the valve should hold a steady vacuum.
- Remove the vacuum pump and voltage source. Connect an ohmmeter to the valve terminals to measure the coil resistance. The resistance should be 36-44 ohms at 68°deg;F (20°deg;C).
- If the valve does not operate as described or if the solenoid coil resistance is not as specified, replace the valve.