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Vacuum Modulator

  1. Disconnect vacuum hoses from ports "P", "Q" and "R" of vacuum modulator. Plug ports "P" and "R" (2 ports on same side) and blow through port "P" (single port on opposite side). Air should escape freely from filter.
  2. Start engine and run at 3000 RPM on vehicles. Repeat blowing test. There should be strong resistance to air flow through modulator. If not, replace modulator. Reconnect vacuum hoses to proper locations.
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