Examination
Models with a carburetor engine
1. If you think the system is faulty, disconnect the hoses from the recirculation valve, backpressure valve, and thermal vacuum valve and purge them. If the hoses are not clogged, reconnect them.
2. Thermal vacuum valve test procedures are described in clause 2 of subsection 6.4.2.3.
3. To check the recirculation valve, disconnect the vacuum hose from the top of the valve and connect another hose to the valve nozzle. Pull in the air from the hose; check that the valve diaphragm rises and quickly returns when you stop drawing air. Diaphragm function can be checked by placing your finger on the underside of the valve where you can feel the movement of the diaphragm. If the diaphragm moves hard or does not move at all, the recirculation valve must be replaced.
4. If you are sure that the thermal vacuum valve is working, the back pressure valve can be checked as follows. Warm up the engine to normal operating temperature and disconnect the vacuum hose from the recirculation valve. Close the opening of the disconnected hose with your finger and briefly increase the engine speed. When the engine speed (and exhaust gas pressure) increases, a vacuum must be present in the tube. When the engine speed drops, the vacuum in the hose must be stopped by the back pressure valve. If it is not, the valve is defective and must be replaced.
All models with fuel injection system
5. The recirculation system can be checked as described in pp. 1–4, skipping information regarding the thermal vacuum valve. Instead of the thermal vacuum valve on these models, a control solenoid valve is installed. This solenoid valve is the same valve that controls the operation of the fuel vapor control system and can be tested as described in pp. 2–5 of subsection 6.4.2.3.