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Home >> GMC >> 1991 >> Value Van 7.4 N >> Repair and Diagnosis >> External Pages >> Different car >> Section 39 (Engine Controls - Tests W/Codes - 5.2L CNG) >> Self-Diagnostic Tests >> Test NTC-8A - Checking Oxygen Sensor Switching

Test NTC-8A - Checking Oxygen Sensor Switching

WARNING: This page is about a different car, the 1995 Dodge Ram Wagon, 1995 Dodge Ram Van, 1995 Dodge Pickup, and 1995 Dodge Dakota. However, it is still accessible from the selected car via links, so may be relevant.
  1. Operate engine at normal operating temperature. Using scan tool, read Oxygen Sensor (O2S) state. If O2S state switches, O2S is okay. Test is complete. If O2S state does not switch and sensor is locked on lean, go to TEST NTC-8B. If O2S state does not switch and sensor is not locked on lean, turn ignition off.
    NOTE: Before opening any part of Compressed Natural Gas (CNG) fuel system for repair, fuel pressure must be released. See FUEL PRESSURE RELEASE  .
  2. If vehicle is equipped with a fuel rail test port, install a 0-300 psi pressure test gauge to fuel rail test port and go to next step. If vehicle is not equipped with a fuel rail test port, release fuel pressure. See FUEL PRESSURE RELEASE  . Connect a 0-300 psi pressure test gauge between Compressed Natural Gas (CNG) low pressure sensor and fuel rail block. Reinstall CNG low pressure sensor to test gauge tee connection. Turn ignition on.
  3. Using scan tool, actuate fuel system. Allow pressure test gauge to stabilize to normal fuel pressure. Stop actuation test. Observe pressure test gauge for 10 seconds. If fuel pressure is less than 10 psi, replace leaking injectors or "O" rings as necessary. Perform TEST VER-2.
  4. If fuel pressure is more than 10 psi, inspect air cleaner filter and inlet ducts for restrictions. Repair as necessary. Perform TEST VER-2. If restrictions are not present, go to TEST NTC-15A.
  5. Turn ignition on. Using scan tool, monitor fuel pressure for 10 seconds. If fuel pressure drops more than 5 psi, go to next step. If fuel pressure does not drop more than 5 psi, inspect air cleaner filter and inlet ducts for restrictions. Repair as necessary. Perform TEST VER-2. If restrictions are not present, go to TEST NTC-15A.
  6. Inspect fuel rail and fuel lines for leaks. Release fuel pressure and repair as necessary. Perform TEST VER-2. If Fuel rail and fuel lines are okay, release fuel pressure and replace leaking injectors or "O" rings as necessary. Perform TEST VER-2.
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