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Test NF-7A - Checking Oxygen (O2) Sensor Switching

WARNING: High fuel pressure may be present in fuel lines. Open fuel system with caution. See FUEL PRESSURE RELEASE procedure.
  1. Allow engine to reach normal operating temperature. Using DRB-II, read O2 sensor states (left and right). If O2 sensor states are switching, system is functioning okay. Test is complete. If O2 sensor states are not switching, check if O2 sensor is locked on lean. If O2 sensor is locked on lean, perform TEST NF-7B. If O2 sensor is not locked on lean, go to next step.
  2. Turn engine off. Release fuel pressure. Install fuel pressure gauge in fuel supply line. Turn ignition on. Using DRB-II, actuate fuel system test. Allow fuel pressure gauge to stabilize to normal fuel pressure. Stop fuel system actuation test. Monitor fuel pressure gauge for one minute.
  3. If fuel pressure gauge reading drops more than 10 psi, replace leaking injector(s) or "O" rings are needed. Perform TEST VER-2. If fuel pressure gauge reading does not drop more than 10 psi, go to next step.
  4. Inspect air cleaner and inlet ducts for restriction(s). Repair as required. Perform TEST VER-2. If no restrictions are observed, go to TEST NF-15A.
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