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HOMESERVICE MANUALSISUZU1996TROOPER S, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 17 (ENGINE CONTROLS - TESTS W/CODES - 2.6L 4-CYL)CIRCUIT TESTINGDTC P0300 - ENGINE MISFIRE DETECTEDDIAGNOSTIC PROCEDURES
1996 Isuzu Trooper S, Automatic

Diagnostic Procedures

1996 Isuzu Trooper S, AutomaticSECTION Diagnostic Procedures
WARNING: This page is about a different car, the 1996 Honda Passport. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform On-Board (OBD) System Check. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Start engine and allow it to idle. Using scan tool, read and record FREEZE FRAME data. Operate vehicle within conditions noted in FREEZE FRAME data. Using scan tool, read MISFIRE CUR # display for each cylinder. If MISFIRE CUR # is increasing (indicating a misfire currently occurring) for any cylinder, go to next step. If MISFIRE CUR # is not increasing, go to DIAGNOSTIC AIDS .
  3. Check vacuum hoses for splits, kinks, or improper connections. If a problem is found, repair as necessary and go to step 18). If no problem is found, go to next step.
  4. Check intake manifold, injector "O" rings, EGR valve, and EGR feed pipes for vacuum leaks. If a problem is found, repair as necessary and go to step 18). If no problem is found, go to next step.
  5. Check PCV valve for improper installation or damaged hose. If a problem is found repair and go to step 18). If no problem is found, go to next step.
  6. Inspect interior of distributor cap for carbon tracking. Check distributor rotor for damage. If a problem is found repair as necessary and go to step 18). If no problem was found, go to next step.
  7. Remove ignition coil. Check ignition coil for cracks or carbon tracking. If a problem is found, replace damaged coil and go to step 18). If no problem is found, go to next step.
  8. Remove EGR valve and inspect valve, seat and passages for damage. Inspect valve pintle to ensure it is not sticking partially open. If a problem is found, repair as necessary and go to step 18). If no problem is found, go to next step.
  9. Install a spark tester on spark plug wire at spark plug end for cylinder indicating most severe misfire. Crank engine and check for crisp, Blue spark at tester. Repeat procedure for each affected cylinder. If spark is okay on all cylinders, go to step 14). If spark is not okay on any cylinder, 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 insulation for cracks, carbon tracking or other damage. If a problem is found, replace faulty spark plug(s) and go to step 18). If no problem is found, go to next step.
  12. Replace ignition control module and go to next step.
  13. Check PCM injector, power and sensor grounds for clean and tight connection, and for proper location. If a problem is found, repair as necessary and go to step 18). If no problem is found, go to next step.
  14. Perform a FUEL PUMP PRESSURE TEST. See BASIC TESTING - 2.6L 4-CYL . If a problem was found, repair as necessary and go to step 18). If no problem was found, go to next step.
  15. Check for fuel contamination. If fuel is contaminated, repair condition causing contamination and go to step 18). If fuel is okay, go to next step.
  16. Perform INJECTOR BALANCE TEST under FUEL SYSTEM in SYSTEM/COMPONENT TESTS - 2.6L 4-CYL article. If a problem is found, repair as necessary and go to step 18). If no problem is found, go to next step.
  17. Diagnose mechanical engine problems such as; faulty or incorrect camshaft, leaking valves or piston rings or sticky valves, excessive valve deposits, loose or worn rocker arms, weak valve springs, incorrect valve timing, leaking head gasket or loose or broken motor mounts. If a problem is found, repair as necessary and go to nest step.
  18. Using scan tool, read and record FREEZE FRAME data. Clear DTCs. Start engine and allow it to idle. Operate vehicle within conditions noted in FREEZE FRAME data. Using scan tool, read MISFIRE CUR # display for each cylinder. If MISFIRE CUR # is not increasing, repair is complete. If MISFIRE CUR # is increasing (indicating a misfire currently occurring) for any cylinder, return tostep 2).
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.