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Home >> Isuzu >> 2002 >> Trooper LS, 4WD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Basic Diagnostic Procedures >> Fuel System >> Fuel System Diagnosis >> Testing Procedure
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Testing Procedure

  1. Perform On-Board Diagnostic II (OBD-II) System Check. See ON-BOARD DIAGNOSTIC II SYSTEM CHECKunder SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing OBD-II system check, go to next step.
  2. Turn ignition off. Turn A/C off. Relieve fuel system pressure. See FUEL SYSTEM PRESSURE RELEASE  . Connect fuel pressure gauge as outlined in FUEL PUMP PRESSURE TEST  . Turn ignition on (fuel pump will run for about two seconds). Using scan tool, command fuel pump On. Fuel pressure should be 42-55 psi (283-376 kPa). If fuel pressure is as specified, go to next step. If fuel pressure is not within specifications, go to step  17 .
  3. Fuel pressure will drop when fuel pump stops running. It should then stabilize and remain constant. If fuel pressure remains constant, go to next step. If fuel pressure does not remain constant, go to step  12 .
  4. With engine warmed up to operating temperature, turn ignition on and observe fuel pressure. Continue to observe fuel pressure while starting engine. Reading should drop 3-15 psi (21-105 kPa). If fuel pressure drops as specified, go to next step. If fuel pressure does not drop as specified, leave pressure gauge connected and go to step  9 .
  5. Test drive vehicle to determine if fuel pressure drops off during acceleration, cruise or hard cornering. If fuel pressure drops, go to next step. If fuel pressure does not drop, check for improper fuel in vehicle. If problem is found, drain fuel and replace as necessary.
  6. Check for restricted fuel filter or fuel feed line. If problem is found, repair as necessary. After repair, test drive vehicle to confirm repair. If no problem was found, go to next step.
  7. Remove fuel tank to inspect for restricted fuel pump strainer, leaking fuel line or incorrect fuel pump. If problem is found, repair as necessary. If no problem was found, go to next step.
  8. Replace fuel pump. See FUEL SYSTEM in REMOVAL, OVERHAUL & INSTALLATION article. After repair, test drive vehicle to confirm repair.
  9. Disconnect fuel pressure regulator vacuum hose. With engine idling, use hand-held vacuum pump to apply 12-14 in. Hg. while observing fuel pressure gauge. Fuel system pressure should drop 3-15 psi (21-105 kPa). If fuel pressure drops as specified, go to next step. If fuel pressure does not drop as specified, go to step  11 .
  10. Inspect fuel pressure regulator vacuum hose for leaks. If problem is found, repair or replace as necessary. Test drive vehicle to confirm repair.
  11. Replace fuel pressure regulator. See FUEL SYSTEM in REMOVAL, OVERHAUL & INSTALLATION article. After repair, test drive vehicle to confirm repair.
  12. Using scan tool command fuel pump On. After pressure builds up, turn off pump and clamp fuel supply hose with locking pliers that will not damage fuel line. Observe fuel pressure. If pressure remains constant, go to next step. If fuel pressure does not remain constant, go to step  15 .
  13. Inspect fuel supply hose for leaks. If problem is found, repair as necessary. If no problem is found, go to next step.
  14. Remove fuel tank and inspect for leaking hose or in-tank fuel line. If problem is found, repair as necessary. If no problem is found, repeat test starting in step  8 .
  15. Remove locking pliers from fuel supply hose, and clamp them to fuel return hose. Using scan tool command fuel pump On. After pressure has built up, turn off power and observe fuel pressure gauge. If fuel pressure reading remains constant, repeat test starting in step  11 . If fuel pressure reading does not remain constant, go to next step.
  16. Locate and replace any leaking fuel injectors. See FUEL SYSTEM in REMOVAL, OVERHAUL & INSTALLATION article. After repair, test drive vehicle to confirm repair.
  17. If fuel pressure indicated on gauge is 55 psi (376 kPa), go to next step. If fuel pressure is less than specified, go to step  21 .
  18. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELEASE  . Disconnect fuel return line from fuel rail. Attach an auxiliary length of flexible fuel hose to fuel rail return outlet and place other end into a suitable container. Using scan tool command fuel pump On. Observe fuel pressure while fuel pump is running. Fuel pressure should be 42-55 psi (290-376 kPa). If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to step  20 .
  19. Locate and repair restriction in fuel return line. After repair, test drive vehicle and confirm repair.
  20. Visually inspect fuel rail outlet passages for restriction. If problem is found, repair or replace as necessary. After repair, test drive vehicle and confirm repair. If no problem was found, go back to step  11 .
  21. If indicated fuel pressure is more than 0 psi (0 kPa), go to next step. If indicated fuel pressure is 0 psi (0 kPa), go to step  23 .
    22. CAUTION: DO NOT let fuel pressure rise above 60 psi (1413 kPa), or fuel pressure regulator damage may result.
  22. Using scan tool command fuel pump On. Observe fuel pressure reading while slowly pinching off fuel return hose. If fuel pressure rises above 55 psi (376 kPa), repeat testing starting in step  11 . If fuel pressure does not rise above 55 psi (376 kPa), repeat testing starting in step  7 .
  23. Using scan tool command fuel pump On. Remove fuel filler cap and listen for fuel pump operation. If fuel pump is running, repeat testing starting in step  7 . If fuel pump is not running, go to FUEL SYSTEM ELECTRICAL TEST  .
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