Reverse Delay Valve (5.9L)

The reverse delay valve improves cold engine driveability and reduces undesirable hydrocarbon (HC) emissions. When engine is started, manifold vacuum applied to the distributor vacuum advance mechanism advances ignition timing. When engine is accelerated, manifold vacuum decreases, causing ignition timing to be retarded. To prevent sudden retarding of ignition timing during acceleration, a one-way reverse delay valve is inserted in the vacuum line to delay the effects of decreasing manifold vacuum.