1986 Mercury Sable LS, 4D SedanFACTORY OEM SERVICE PROCEDURE

Normally Open Valve With Vacuum Vent

  1. With engine at normal operating temperature, parking brake applied, and transmission in "P" or "N", disconnect air supply line at valve outlet. Disconnect all vacuum lines from vacuum nipple and vent.
  2. With engine at 1500 RPM, air pump supply should be heard and felt at outlet. Connect a vacuum line from vacuum nipple to one of vacuum fittings on intake manifold. With vacuum vent open to atmosphere, and engine speed at 1500 RPM, no air should be felt at outlet, since all air is by-passed through silencer ports.
  3. Using same direct line to an intake manifold vacuum source, cap vacuum vent. Increase engine speed to 2000 RPM and suddenly release throttle. A momentary interruption of air pump supply should be felt at valve outlet.
  4. If valve fails any test and air pump is operating properly, replace valve. Reconnect all vacuum and thermactor lines.
Factory Service Tools

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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