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Home >> Suzuki >> 2003 >> XL-7 Base, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 4 (Engine Controls - Self-Diagnostics) >> Diagnostic Tests >> DTC P0300: Engine Misfire Detected >> Diagnostic Procedure
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Diagnostic Procedure

WARNING: This page is about a different car, the 2002 Isuzu Trooper. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform ON-BOARD DIAGNOSTIC II SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. After performing OBD-II system check, go to next step.
  2. Start engine and run at idle. Using scan tool, read and record FREEZE FRAME data. Operate vehicle within FAILURE RECORDS conditions. Using scan tool, observe MISFIRE CUR. # display for each cylinder. If MISFIRE CUR. # increases (indicating an occurring misfire) for any cylinder, go to next step. If MISFIRE CUR. # does not increase, check for an intermittent problem. See DIAGNOSTIC AIDS .
  3. Check vacuum hoses for splits, kinks or improper connections. If a problem is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, go to next step.
  4. Check intake manifold, injector "O" rings, EGR valve, EGR feed pipes and ION sensing module for vacuum leaks. If a problem is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, go to next step.
  5. Check PCV valve for improper installation, damaged hose or grommet. If a problem is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, go to next step.
  6. Inspect MAF inlet screen for damage or foreign objects that may block airflow to MAF sensor. If problem is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, go to next step.
  7. Remove EGR valve and inspect valve, seat and passages for carbon deposits or damage. Inspect valve pintle to ensure it is not sticking partially open. If a problem is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, go to next step.
  8. Install a spark tester on spark plug end of ignition coil for cylinder indicating a misfire. Crank engine and check for a strong Blue spark. Repeat procedure for each affected cylinder. If spark is okay on all cylinders, go to step  14. If spark is not okay at all cylinders, go to next step.
  9. Remove ignition coil related to misfiring cylinder. Check ignition coil for cracks or carbon tracking. If a problem is found, replace damaged ignition coil. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, go to next step.
  10. Remove spark plug(s) associated with misfiring cylinder(s). Check spark plugs for excessive fouling. If spark plugs are excessively fouled, diagnose and repair mechanical engine problem. If spark plugs are not excessively fouled, go to next step.
  11. Check spark plug insulators for cracks, carbon tracking or other damage. If a problem is found, replace faulty spark plug(s). After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, go to next step.
  12. Turn ignition off. Disconnect MAF sensor 3-pin harness connector. Start and run engine until vehicle is operating in closed loop. Using scan tool, observe BANK 1 L.T. FUEL TRIM and BANK 1 S.T. FUEL TRIM parameters. If L.T. FUEL TRIM decreases to less than 20 percent and S.T. FUEL TRIM decreases to less than 50 percent, go to next step. If scan tool display is not as specified, replace ignition coil related to affected cylinder. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM.
    13. NOTE: Ignition coil control module is part of ION sensing module system.
  13. Replace ignition coil control module. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM.
  14. Ensure PCM injector ground, power grounds and sensor grounds are clean and tight. If a problem is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If connections are okay, go to next step.
  15. Perform fuel pressure test. See FUEL SYSTEM PRESSURE TEST under BASIC FUEL SYSTEM CHECKS in BASIC DIAGNOSTIC PROCEDURES article. If a problem was found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem was found, go to next step.
  16. Check for fuel contamination. If fuel is contaminated, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If fuel is okay, go to next step.
  17. Perform FUEL INJECTOR BALANCE TEST under FUEL SYSTEM in SYSTEM & COMPONENT TESTING article. If a problem is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, go to next step.
  18. Diagnose mechanical engine problems such as faulty camshaft, leaking or sticking valves, excessive valve deposits, weak valve springs, damaged piston rings, loose or worn rocker arms, incorrect valve timing, leaking head gasket or loose or broken motor mounts. If a problem is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problems are found, go to next step.
  19. Check for a transmission Torque Converter Clutch (TCC) problem. See appropriate article in AUTOMATIC TRANSMISSIONS. If problem is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, go to next step.
  20. Replace MAF sensor. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM.
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