### Boost Control Deceleration Device (BCDD)

The Boost Control Deceleration Device (BCDD) used to reduce hydrocarbon emissions during coasting conditions.

High manifold vacuum during coasting prevents the complete combustion of the air/fuel mixture because of the reduced amount of air. This condition will result in a large amount of HC emission. Enriching the air/fuel mixture for a short time (during the high vacuum condition) will reduce the emission of the HC.

However, enriching the air/fuel mixture with only the mixture adjusting screw will cause poor engine idle or invite an increase in the carbon monoxide (CO) content of the exhaust gases. The BCDD consists of an independent system that kicks in when the engine is coasting and enriches the air/fuel mixture, which reduces the hydrocarbon content of the exhaust gases. This is accomplished without adversely affecting engine idle and the carbon monoxide content of the exhaust gases.