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Home >> Mitsubishi >> 2000 >> Galant LS >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0300: Random Misfire Detected >> Diagnostic Procedures

Diagnostic Procedures

  1. Connect scan tool to OBD-II Data Link Connector (OBD-II DLC), located below center of instrument panel. Start engine and let idle. Using scan tool, check data list item No. 22 (crankshaft position sensor). Check waveform of CKP sensor pulse width by keeping engine speed constant. If CKP sensor pulse width is constant, go to next step. If CKP sensor pulse width is not constant, check CKP sensor circuit. See DTC P0335: CRANKSHAFT POSITION (CKP) SENSOR CIRCUIT MALFUNCTION  .
  2. Warm-up engine. 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 P0170 OR P0173: FUEL TRIM MALFUNCTION  .
  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 -10-10 percent (2.4L) or -25-25 percent (3.0L). If fuel trim is as specified, go to next step. If fuel trim is not as specified, check fuel trim fault. See DTC P0170 OR P0173: FUEL TRIM MALFUNCTION  .
  4. 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. Check spark plug gap. Gap should be .039-.043" (1.0-1.1 mm). If problem exists, adjust gap, or replace plugs, then go to step  13 . If problem does not exist, go to next step.
  6. Remove plug wires and check resistance. Maximum resistance for each plug wire is 22 k/ohms. If any plug wire resistance is more than specified, replace appropriate plug wire, then go to step  13 . If plug wire resistances are okay, check ignition circuit. See IGNITION CHECKS in BASIC DIAGNOSTIC PROCEDURES article. If problem exists, repair as necessary. If problem does not exist, go to next step.
  7. Disconnect fuel injector connectors. Check resistance between fuel injector terminals. Resistance should be 13-16 ohms at 68°F (20°C). If resistance is as specified, go to next step. If resistance is not as specified, replace appropriate fuel injector(s), then go to step  13 .
  8. Check fuel injector connectors. If problem exists, repair appropriate connector, then go to step  13 . If problem does not exist, go to next step.
  9. Check ECM 26-pin connector C-35 or PCM 35-pin connector C-39. If problem exists, repair appropriate connector, then go to step  13 . If problem does not exist, go to next step.
  10. On 3.0L check and right bank fuel injector intermediate connector. On all vehicles, check wiring between injectors and ECM/PCM. If problem exists, repair as necessary, then go to step  13 . If problem does not exist, go to next step.
  11. Check valve timing. See appropriate article in ENGINES. 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 exists, repair as necessary, then go to step  13 . If problem does not exist, go to next step.
  12. Replace all injectors. Using scan tool, clear DTCs. Test drive vehicle following OBD-II drive cycle other monitor pattern. See OBD-II DRIVE CYCLES under VERIFYING REPAIRS in SELF-DIAGNOSTICS - INTRODUCTION article. Check for DTCs. See VERIFYING REPAIRS in SELF-DIAGNOSTICS - INTRODUCTION article. If DTC P0300 is not output, inspection is complete. If DTC P0300 is output, replace ECM/PCM, then go to next step.
  13. Using scan tool, clear DTCs. Test drive vehicle following OBD-II drive cycle other monitor pattern. See OBD-II DRIVE CYCLES under VERIFYING REPAIRS in SELF-DIAGNOSTICS - INTRODUCTION article. Check for DTCs. Confirm DTC P0300 does not reset. See VERIFYING REPAIRS in SELF-DIAGNOSTICS - INTRODUCTION article.
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