C 1500 1/2 Ton Pickup 2WD V8-305 5.0L VIN H 4-bbl (1982)
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Vacuum Check Valve: Description and Operation
OPERATION
Solenoid--energized by the ECM during cold engine operation--blocks ported vacuum to the EGR valve.
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When engine temperature is at or above the value programmed into the ECM, the module de-energizes the solenoid, which then directs ported
vacuum to the EGR valve, activating the EGR system.