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Testing Diaphragm-Operated Purge Valve

  1. Attach a short hose to PCV inlet orifice (lower tube) of evaporative canister, and try to blow through it. See Fig 1 .
  2. Little or no air should pass into the canister. A small amount of air will pass through if canister has a constant purge hose. Using a hand-held vacuum pump, apply 15 in. Hg to control vacuum signal port.
  3. If diaphragm does not hold vacuum for at least 20 seconds, replace canister. If diaphragm holds vacuum, try to blow through PCV hose again. An increase in airflow should be observed. If air does not flow, replace canister.
Fig 1: Identifying Evaporative Emission Control System Components
G121791Courtesy of GENERAL MOTORS CORP.
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