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1974 Models

  1. Disconnect vacuum hose at distributor advance diaphragm and connect vacuum gauge to it. With engine cold and running at 2000 RPM, vacuum gauge should read normal vacuum. Vacuum reading should drop to zero (0) as engine temperature rises.
  2. If no vacuum is available with engine cold, stop engine. Disconnect and plug vacuum hose from idle cut-off valve at charcoal canister. Start engine and set at fast idle speed. If vacuum is not available, check idle cut-off valve. Replace if necessary.
  3. If vacuum is still not available, stop engine. Disconnect vacuum hose to solenoid valve and connect vacuum gauge to it. If vacuum is present, solenoid valve is defective. Replace solenoid valve and recheck system. If no vacuum is present, clean manifold vacuum port.
  4. Stop engine. If vacuum is available in 1st, 2nd or 3rd gear with engine above 122°F (50°C), but below normal operating temperature at fast idle. Check continuity between coolant temperature switch terminals.
  5. If no continuity exists, replace defective coolant temperature switch. If continuity exists, check for battery voltage at solenoid valve with engine running.
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