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

  1. If using scan tool only, go to next step. If using lab scope, connect pick-up to CKP sensor connector terminal No. 2 or ECM connector terminal No. 43. Start and idle engine. Check waveform of CKP sensor with engine speed constant. Normal pattern is square wave, even pulse width, that toggles between near zero volts and near 5 volts. If CKP sensor pulse width is constant, go to step  5 . If CKP sensor pulse width is not constant, go to next step.
  2. Connect tachometer. Using scan tool, read data list item No. 22 (crankshaft position sensor). Cranking speed on scan tool should match tachometer. If tachometer reads zero RPM while cranking, check for bad CKP sensor or broken timing belt. If scan tool reading matches tachometer, go to next step.
  3. Run engine at idle. Closed throttle position switch should be on. Using scan tool, read data list item No. 22 (crankshaft position sensor). Compare scan tool readings with normal values. See CKP SENSOR SCAN TOOL VALUES  table. If scan tool readings are as specified, go to step  5 . If scan tool readings are not as specified, go to next step.
    CKP SENSOR SCAN TOOL VALUES

    Coolant Temperature - °F (°C) RPM
    -4 (-20) 1300-1475
    32 (0) 1300-1500
    68 (20) 1300-1500
    104 (40) 1040-1240
    176 (80) 600-800
  4. Check CKP sensor connector, ECM connector and wiring between ECM and CKP sensor connector. Check CKP sensor and sensing plate for proper installation. If problem exists, repair as necessary, then go to step  10 . If problem does not exist, replace CKP sensor, then go to step  10 .
  5. Check injectors and injector circuit. See DTC P0201-P0206: FUEL INJECTOR CYLINDER NO. 1-4 CIRCUIT MALFUNCTION  . If problem exists, repair as necessary. If problem does not exist, go to next step.
  6. Start and warm engine. Turn all accessories off. Using scan tool, read data list item No. 81 (long-term fuel compensation). At idle, fuel trim should be -12.5-12.5 percent (during closed loop). If fuel trim is as specified, go to next step. If fuel trim is not as specified, check fuel trim fault. See DTC P0170 & P0173: FUEL TRIM MALFUNCTION  .
  7. Using scan tool, read data list item No. 82 (short-term fuel compensation). At 2500 RPM in closed loop operation with no load, fuel trim should be -30-25 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 & P0173: FUEL TRIM MALFUNCTION  .
  8. Using scan tool, read data list item No. 21 (engine coolant temperature). If temperature displayed on scan tool is equal to actual engine coolant temperature as measured with a thermometer, go to next step. If temperature displayed on scan tool is not equal to actual coolant temperature, check ECT circuit. See DTC P0115: ENGINE COOLANT TEMPERATURE (ECT) CIRCUIT MALFUNCTION  .
  9. Check valve timing. See appropriate article in ENGINES. Check engine compression, ignition coil, spark plugs and spark plug wires. See BASIC DIAGNOSTIC PROCEDURES article. Check EGR system and fuel injectors. See SYSTEM & COMPONENT TESTING article. Repair as necessary, then go to next step.
  10. Connect all disconnected components. Using scan tool, clear DTCs. Test drive vehicle following other monitor drive cycle pattern. See OBD-II DRIVE CYCLES under VERIFYING REPAIRS in SELF-DIAGNOSTICS - INTRODUCTION article. Check for DTCs. Confirm DTC does not reset. See VERIFYING REPAIRS in SELF-DIAGNOSTICS - INTRODUCTION article.
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