DESCRIPTION
This system controls emissions of HC and CO during sudden deceleration. This is accomplished through a mixture control valve which allows additional fresh air to enter the intake manifold when sudden deceleration (closed throttle) occurs.
OPERATION
When sudden deceleration occurs, high manifold vacuum acts on chamber B of mixture control valve. The valve opens and fresh air is drawn in through MC valve filter to intake manifold where it helps maintain a balanced air/fuel mixture. After a few seconds, vacuum in chamber A will balance vacuum in chamber B. The MC valve closes and no additional air is brought into intake manifold. Deceleration fuel control is then maintained by throttle positioner or deceleration fuel cut system.
SYSTEM TESTING
- Remove air cleaner cover and air filter. Start engine. Disconnect vacuum sensing hose from mixture control valve and block hose.
- Place hand over air inlet of mixture control valve. Vacuum should not be felt.
- Now, check that vacuum is felt momentarily when hose is connected. At this time, engine will develop rough idle or die. This is normal. Reconnect all hoses, air filter and air cleaner cover.