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Home >> Mitsubishi >> 2002 >> Montero XLS >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0300: Random Misfire Detected >> Test Procedures

Test Procedures

  1. Start engine and let idle. Using scan tool, check data list item No. 22 (crankshaft position sensor). Check waveform of CKP sensor while keeping engine speed constant. If CKP sensor waveform pulse width is constant, go to next step. If CKP sensor waveform pulse width is not constant, check CKP sensor circuit. See DTC P0335: CRANKSHAFT POSITION (CKP) SENSOR CIRCUIT MALFUNCTION .
  2. Ensure engine is at normal operating temperature. Turn all accessories off. Increase engine speed to 2500 RPM. Using scan tool, check data list item No. 81 (long-term fuel compensation). At 2500 RPM in closed loop, fuel trim should be -12.5-12.5 percent. If fuel trim is as specified, go to next step. If fuel trim is not as specified, check fuel trim fault. See DTC P0171: RIGHT BANK SYSTEM TOO LEAN (BANK 1) , DTC P0172: RIGHT BANK SYSTEM TOO RICH (BANK 1) , DTC P0174: LEFT BANK SYSTEM TOO LEAN (BANK 2)  or DTC P0175: LEFT BANK SYSTEM TOO RICH (BANK 2)  .
  3. Using scan tool, check data list item No. 82 (short-term fuel compensation). At 2500 RPM in closed loop operation, fuel trim should be -10.0-10.0 percent. If fuel trim is as specified, go to next step. If fuel trim is not as specified, check fuel trim fault. See DTC P0171: RIGHT BANK SYSTEM TOO LEAN (BANK 1) , DTC P0172: RIGHT BANK SYSTEM TOO RICH (BANK 1) , DTC P0174: LEFT BANK SYSTEM TOO LEAN (BANK 2)  or DTC P0175: LEFT BANK SYSTEM TOO RICH (BANK 2)  .
  4. Remove intake manifold. See INTAKE MANIFOLD under REMOVAL & INSTALLATION in appropriate article in ENGINES. Remove spark plugs and connect to plug wire. Ground spark plug electrode and crank engine. If spark plug fires when engine is cranked, go to step  7. If spark plug does not fire, go to next step.
    5. NOTE: DO NOT adjust gap on platinum plugs.
  5. Check spark plug gap. Gap should be .039-.043" (1.0-1.1 mm). If problem does not exist, go to next step. If problem exists, replace plugs. Go to step  13.
  6. Remove plug wires and measure resistance. Maximum resistance for each plug wire is 22 k ohms. If any plug wire resistance is more than specified, replace appropriate plug wire. Go to step  13. If plug wire resistances are okay, check ignition circuit. See IGNITION CHECKS in BASIC DIAGNOSTIC PROCEDURES article. Repair as necessary. Then go to next step.
  7. Disconnect fuel injector connectors. Measure resistance between fuel injector connector terminals (component side). Resistance should be 13-16 ohms at 68°F (20°C). If each resistance is as specified, go to next step. If any resistance is not as specified. Go to step  13.
  8. Check fuel injector connectors and fuel injector intermediate connector B-44 for loose, damaged, or corroded terminals. If problem does not exist, go to next step. If problem exists, repair appropriate connector(s). Go to step  13.
  9. Disconnect PCM connector D-107. Check PCM connector D-107 for loose, damaged, or corroded terminals. If problem does not exist, go to next step. If problem exists, repair appropriate connector. Go to step  13.
  10. Check for continuity in wiring between each fuel injectors connector terminals No. 2 and PCM connector D-107. See FUEL INJECTOR TO INTERMEDIATE CONNECTOR TO PCM PIN DESIGNATIONS  for connector terminal identification. There should be continuity. Then, check for continuity in wiring between ground and each fuel injectors connector terminals No. 2. There should be no continuity. If continuity is as specified, go to next step.

    If continuity is not as specified, repair appropriate wire between suspect fuel injector(s) connector terminals No. 2 and PCM connector D-107. Go to step  13.

  11. Check valve timing belt. See TIMING BELT INSPECTION under TIMING BELT in ENGINES - MECHANICAL 3.5L V-6 article. Check engine compression. See MECHANICAL INSPECTION under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES article. Check EGR system. See EXHAUST GAS RECIRCULATION (EGR) under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING article. If problem does not exist, go to next step. If problem exists, repair as necessary. Go to step  13.
  12. Replace all injectors. Install intake manifold. See INTAKE MANIFOLD under REMOVAL & INSTALLATION in appropriate article in ENGINES. Test drive vehicle following OBD-II drive cycle Other Monitor pattern. See OTHER MONITOR  under OBD-II DRIVE CYCLES under VERIFYING REPAIRS. Check for DTCs. If DTC P0300 is output, replace PCM. Go to step  14. If DTC P0300 is not output, inspection is complete.
  13. Install intake manifold. See INTAKE MANIFOLD under REMOVAL & INSTALLATION in appropriate article in ENGINES. Then go to next step.
  14. Test drive vehicle following OBD-II drive cycle Other Monitor pattern. See OTHER MONITOR  under OBD-II DRIVE CYCLES under VERIFYING REPAIRS. Check for DTCs. If DTC P0300 is output, go to step  1, and retry diagnostic procedure. If DTC P0300 is not output, inspection is complete.
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