E 350 Van L6-300 4.9L VIN E 1-bbl (1982)
Vacuum Delay Valve: Description and Operation
Delay Vacuum Bypass (DVB)
Delay vacuum bypass system - DVB
Some vehicles are equipped with a delay vacuum bypass system as a part of the spark delay system (SDV).
On all vehicles, Fig. 16, the DVB system is activated by a ported vacuum switch (PVS) and allows full spark port vacuum to the distributor
vacuum advance when coolant is below PVS opening temperature. The system uses a spark delay valve (SDV), a check valve, and a 4 port PVS.
When closed, the two bottom ports of the PVS are used. After opening, the top two ports are used, allowing vacuum to be routed through the SDV.
