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Home >> Pontiac >> 2001 >> Aztek Base, AWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Basic Diagnostic Procedures >> Basic Fuel System Checks (Gasoline) >> Fuel System Pressure Test >> 4.8L, 5.3L & 6.0L
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4.8L, 5.3L & 6.0L

  1. Perform OBD system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. After performing OBD system check, go to next step.
  2. Turn ignition off. Turn A/C system off. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF . Install Fuel Pressure Gauge (J-34730-1A). Place fuel pressure gauge bleed hose into container. Turn ignition on. Bleed air from fuel pressure gauge. Turn ignition off for 10 seconds. Turn ignition on. Fuel pump should run for about 2 seconds. Cycle ignition to obtain highest fuel pressure possible. Observe fuel pressure with fuel pump running. Fuel pressure should be 55-62 psi (3.9-4.4 kg/cm2 ). If fuel pressure is within specification, go to next step. If fuel pressure is not within specification, go to step  12.
  3. Fuel pressure may vary slightly when fuel pump stops. After fuel pump stops, fuel pressure should stabilize and remain constant. Note fuel pressure when fuel pump stops running. If fuel pressure decreases more than 5 psi (0.3 kg/cm2 ) in 10 minutes, go to step  10. If fuel pressure does not decrease more than 5 psi (0.3 kg/cm2 ) in 10 minutes, go to next step.
  4. Relieve fuel pressure until pressure is 10 psi (0.7 kg/cm2 ). If fuel pressure decreases more than 2 psi (0.1 kg/cm2 ) in 10 minutes, go to step  19. If fuel pressure does not decrease more than 2 psi (0.1 kg/cm2 ) in 10 minutes, go to next step.
  5. If fuel pressure is suspected of decreasing during acceleration, cruise or hard cornering, go to next step. If fuel pressure is not suspected of decreasing during acceleration, cruise or hard corning, go to step  8.
  6. Inspect in-line fuel filter and fuel feed pipe for restriction. If restriction is found, go to step  24. If no restriction is found, go to next step.
  7. Remove fuel sending unit assembly. Inspect fuel pump strainer for restriction, proper positioning and installation on fuel sending unit assembly. Check fuel pump flex pipe for leaks and ensure fuel pump is correct for vehicle application. If a problem is found, go to step  24. If no problem is found, go to step  19.
  8. Turn ignition off for 10 seconds. Turn ignition on. Fuel pump should run for about 2 seconds. Cycle ignition to obtain highest fuel pressure possible. Note fuel pressure. Start engine and allow it to reach normal operating temperature. If fuel pressure is less than previously noted pressure by 3-10 psi (0.2-0.7 kg/cm2 ), see appropriate TROUBLE SHOOTING - NO CODES article. If fuel pressure is not less than previously noted pressure by 3-10 psi (0.2-0.7 kg/cm2 ), go to next step.
  9. Disconnect vacuum hose from fuel pressure regulator. With engine idling, apply vacuum (12-14 in. Hg) to fuel pressure regulator. If fuel pressure decreases by 3-10 psi (0.2-0.7 kg/cm2 ), go to step  20. If fuel pressure does not decrease by 3-10 psi (0.2-0.7 kg/cm2 ), go to step  21.
  10. Turn ignition off. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF . Install appropriate fuel line shutoff valves in-line at fuel feed and fuel return lines. Open both shutoff valves. Using scan tool, pressurize fuel system. Wait for fuel pressure to build. Close shutoff valve at fuel feed line. If fuel pressure remains constant, go to step  19. If fuel pressure does not remain constant, go to next step.
  11. Open shutoff valve at fuel feed line. Using scan tool, pressurize fuel system. Wait for fuel pressure to build. Close shutoff valve at fuel return line. If fuel pressure remains constant, go to step  21. If fuel pressure does not remain constant, go to step  22.
  12. If fuel pressure is greater than 62 psi (4.4 kg/cm2 ), go to next step. If fuel pressure is not greater than 62 psi (4.4 kg/cm2 ), go to step  15.
  13. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF . Disconnect fuel return pipe from fuel rail. Attach flexible fuel hose to fuel rail return outlet passage. Place other end of flexible hose into container. Turn ignition off for about 10 seconds. Turn ignition on. Observe fuel pressure gauge with fuel pump running. Fuel pressure should be 55-62 psi (3.9-4.4 kg/cm2 ). If fuel pressure is within specification, go to step  23. If fuel pressure is not within specification, go to next step.
  14. Inspect fuel rail outlet passage for restriction. If restriction is found, go to step  24. If no restriction is found, go to step  21.
  15. If fuel pressure is greater than zero psi, go to next step. If fuel pressure is zero psi, go to step  17.
  16. Turn ignition off. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF . Install appropriate fuel line shutoff valve in-line at fuel return line. Open shutoff valve. Using scan tool, pressurize fuel system. DO NOT allow fuel pressure to exceed 75 psi (5.3 kg/cm2 ). Excess pressure may damage fuel pressure regulator. Wait for fuel pressure to build. Gradually close shutoff valve at return line. If fuel pressure increases to greater than 62 psi (4.4 kg/cm2 ), go to step  21. If fuel pressure does not increase to greater 62 psi (4.4 kg/cm2 ), go to step  7.
  17. Using scan tool, command fuel pump on. If fuel pump runs, go to next step. If fuel pump does not run, check fuel pump electrical circuit. See appropriate diagnostic procedure under NO-START DIAGNOSIS .
  18. Remove fuel sending unit assembly. Inspect in-line fuel filter, fuel feed pipe and fuel pump strainer for restrictions. Check fuel pump flex pipe for leaks. If a problem is found, go to step  24. If no problem is found, go to next step.
  19. Replace fuel sending unit assembly.
  20. Locate and repair loss of vacuum to fuel pressure regulator.
  21. Replace fuel pressure regulator.
  22. Locate and replace leaking fuel injector(s).
  23. Locate and repair restriction in fuel return pipe.
  24. Repair problem as necessary.
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