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HOMESERVICE MANUALSGMC1981VANDURA SPECIAL AUTOMATIC TRANS, TRANS MFR CD 400/M40REPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE MECHANICALFUEL SYSTEMEVAPORATIVE EMISSIONS SYSTEMTESTINGBOWL VENT VALVE
1981 GMC Vandura Special Automatic Trans, Trans Mfr CD 400/M40

Bowl Vent Valve

1981 GMC Vandura Special Automatic Trans, Trans Mfr CD 400/M40SECTION Bowl Vent Valve
  1. Remove bowl vent vapor hose from carburetor. Check open condition of valve by connecting to a manual vacuum pump. It should not be possible to draw more than 0.5" Hg if valve is open (as when engine is off).
  2. If high resistance or plugged system is found, check for plugged or restricted hose. Hose may be cleared with compressed air. If hose is clear, remove canister filter. If restriction persists, replace canister.
  3. To check valve closed position, run engine at idle. Manifold vacuum will be applied to valve through control line. Bowl vent line should exhibit a plugged condition.
  4. If valve is not closed, remove control vacuum line and check for vacuum. If no vacuum, check for hose restriction or leak. Replace hose if required. If vacuum is present, replace canister assembly.
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Stop DIY work and contact a certified mechanic immediately if any of the following apply:

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  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
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