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Home >> Isuzu >> 1996 >> Hombre S >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Basic Testing >> Trouble Shooting >> Fuel System Diagnosis

Fuel System Diagnosis

WARNING: Relieve fuel pressure before connecting fuel pressure gauge. See FUEL SYSTEM PRESSURE RELEASE  under FUEL SYSTEM.
  1. Perform On-Board Diagnostic (OBD) System Check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  . After performing OBD system check, go to next step.
  2. Relieve fuel system pressure. See FUEL SYSTEM PRESSURE RELEASE under FUEL SYSTEM. Install Fuel Pressure Gauge (J-29658-D) . Turn ignition on. Fuel pump should run for 2 seconds (it may be necessary to turn ignition on several times to obtain highest possible fuel pressure). If fuel pressure is 41-47 psi (2.9-3.3 kg/cm2 ), go to next step. If fuel pressure is not 41-47 psi (2.9-3.3 kg/cm2 ), go to step 11).
  3. After fuel pump has shut off, fuel pressure should stabilize and remain constant. If fuel pressure remains constant, go to next step. If fuel pressure does not remain constant, go to step 9).
  4. If fuel pressure is suspected of dropping off during acceleration, cruise or hard cornering, go to next step. If fuel pressure is okay, go to step 7).
  5. Inspect fuel filter and fuel supply line. If restriction is found, go to step 25). If no restriction is found, go to next step.
  6. Remove fuel pump. Inspect fuel pump strainer for a restriction. Check fuel pump coupling hose for leaks. Verify correct fuel pump is installed. If a problem is found, go to step 25). If no problem is found, go to step 21).
  7. Turn ignition on. Start engine. Allow engine to idle at normal operating temperature. If fuel pressure does not drop 3-10 psi (0.2-0.7 kg/cm2 ), go to next step. If fuel pressure drops 3-10 psi (0.2-0.7 kg/cm2 ), system is operating properly. If driveability problem still exists, go to TESTS W/O CODES article.
  8. Disconnect vacuum hose to fuel pressure regulator. With engine at idle, apply 12-14 in. Hg. of vacuum to fuel pressure regulator. If fuel pressure drops 3-10 psi (0.2-0.7 kg/cm2 ), go to step 19). If fuel pressure does not drop 3-10 psi (0.2-0.7 kg/cm2 ), go to step 20).
  9. Turn ignition off. Place bleed hose of fuel pressure gauge into approved gasoline container. Turn ignition on. Bleed air out of fuel pressure gauge. Using scan tool, pressurize fuel system. Pinch fuel pressure gauge inlet hose. If fuel pressure does not remain constant, go to next step. If fuel pressure remains constant, go to step 21).
  10. Using scan tool, pressurize fuel system. Pinch fuel return hose. If fuel pressure does not remain constant, go to step 22). If fuel pressure remains constant, go to step 20).
  11. If fuel pressure is greater than 47 psi (3.3 kg/cm2 ), go to next step. If fuel pressure is not greater than 47 psi (3.3 kg/cm2 ), go to step 15).
  12. Place bleed hose of fuel pressure gauge into approved gasoline container. Open relief valve to relieve fuel pressure. Disconnect fuel return hose fitting. Place end of hose into approved gasoline container. Turn ignition off for about 10 seconds. Turn ignition on. If fuel pressure is 41-47 psi (2.9-3.3 kg/cm2 ), go to step 23). If fuel pressure is not 41-47 psi (2.9-3.3 kg/cm2 ), go to next step.
  13. Inspect fuel return outlet passages for a restriction. If restriction is found, go to step 25). If no restriction is found, go to next step.
  14. Remove fuel pressure regulator. Inspect fuel pressure regulator filter screen for a restriction. If restriction is found, go to step 24). If no restriction is found, go to step 20).
  15. If fuel pressure is greater than 0 psi (0 kg/cm2 ), go to next step. If fuel pressure is not greater than 0 psi (0 kg/cm2 ), go to step 17).
    CAUTION: In the next step, DO NOT  allow fuel pressure to exceed 60 psi (4.2 kg/cm2 ), or fuel pressure regulator or fuel pressure gauge may be damaged.
  16. Place bleed hose of fuel pressure gauge into approved gasoline container. Open relief valve to relieve fuel pressure. Using scan tool, pressurize fuel system. Bleed air out of fuel pressure gauge. Allow fuel pressure to build. Pinch fuel pressure gauge outlet hose. If fuel pressure is greater than 47 psi (3.3 kg/cm2 ), go to step 20). If fuel pressure is not greater than 47 psi (3.3 kg/cm2 ), go to step 6).
  17. Check for problem in fuel system electrical system. See FUEL SYSTEM under ENGINE CRANKS BUT WILL NOT RUN  . If electrical problem was found, go to step 25). If no problem was found, go to next step.
  18. Check in-line fuel filter, fuel feed pipe and fuel pump strainer for restriction. Check fuel pump coupling hose for leaks. If problem was found, go to step 25). If no problem was found, go to step 21).
  19. Locate and repair loss of vacuum to fuel pressure regulator. See VACUUM DIAGRAMS article. After repairs, go to step 26).
  20. Replace fuel pressure regulator. After repairs, go to step 26).
  21. Replace fuel pump. After repairs, go to step 26).
  22. Locate and replace leaking fuel injector(s). After repairs, go to step 26).
  23. Locate and repair restriction in fuel return pipe. After repairs, go to step 26).
  24. Remove and discard fuel pressure regulator filter screen. After repairs, go to step 26).
  25. Repair as necessary. After repairs, go to next step.
  26. Clear DTC(s) using scan tool. Attempt to start engine. If engine starts. go to next step. If engine does not start or starts and dies/stalls, go to step 2).
  27. Warm engine to normal operating temperature. Check if any DTCs are set. If any DTCs are present, diagnose DTC(s). See appropriate TESTS W/CODES article.
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