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Fuel System Pressure Test

WARNING: Begin fuel system trouble shooting and diagnosis with fuel system pressure test. Relieve fuel system pressure before disconnecting any components or installing fuel pressure gauge.
  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 pressure. See FUEL SYSTEM PRESSURE RELIEF  . Connect Fuel Pressure Gauge (J-34730-1A) to fuel pressure connector. Turn ignition on with engine off. With fuel pump running, fuel pressure should be 41-47 psi (2.9-3.3 kg/cm2 ). If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to step 12).
  3. Wait for fuel pump to stop running. Observe fuel pressure after 10 minutes. Fuel pressure should remain within 5 psi (.35 kg/cm2 ) of specified pressure. If pressure drops more than 5 psi (.35 kg/cm2 ), go to step 10). If pressure remains within 5 psi (.35 kg/cm2 ) of specified pressure, go to next step.
  4. Relieve fuel pressure until pressure is 10 psi (.7 kg/cm2 ). Observe fuel pressure after 10 minutes. Fuel pressure should remain within 2 psi (.14 kg/cm2 ) of specified pressure. If pressure drops more than 2 psi (.14 kg/cm2 ), go to step 19). If pressure remains within 2 psi (.14 kg/cm2 ) of specified pressure, go to next step.
  5. If fuel pressure is suspected of dropping off during acceleration, cruise or hard cornering, go to next step. If fuel pressure is as specified, go step 8).
  6. Inspect fuel filter and fuel supply line. Repair or replace as necessary. After repairs, go to step 24). If fuel filter and fuel supply line are okay, go to next step.
  7. Remove fuel sending unit from fuel tank. Inspect fuel pump strainer for restriction, position of fuel pump strainer, fuel pump flex pipe for leaks, or verify if fuel pump is of right application. Repair or replace as necessary. After repairs, go to step 24). If no problems are found, go to step 19).
  8. Turn ignition off for 10 seconds. Turn ignition on. Start and warm engine to normal operating temperature. Allow engine to idle. Observe fuel pressure gauge. Fuel pressure should drop 3-10 psi (.2-.7 kg/cm2 ). If fuel pressure drop is as specified, see the TESTS W/O CODES article. If fuel pressure drop is not as specified, go to next step.
  9. Disconnect vacuum hose to fuel pressure regulator. With engine at idle, apply 12-14" Hg vacuum to fuel pressure regulator, using a vacuum pump. Fuel pressure should drop 3-10 psi (.2-.7 kg/cm2 ). If fuel pressure drop is as specified, go to step 20). If fuel pressure drop is not as specified, go to step 21).
  10. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF  . Connect Fuel Pressure Gauge (J-34730-1A) to fuel pressure connector. Install Fuel Pipe Shut-Off Adapter (J-37287) between fuel feed line and return line. Open valve on shut-off adapter. Using scan tool, pressurize fuel system. Bleed air out of fuel gauge. Wait for pressure to build up. Close valve in fuel shut-off adapter. If fuel pressure remains constant, go to step 19). If fuel pressure does not remain constant, go to next step.
  11. Open fuel shut-off adapter valve. Using scan tool, pressurize fuel system. Wait for pressure to build up. Close shut-off valve. 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 47 psi (3.3 kg/cm2 ), go to next step. If fuel pressure is less than 47 psi (3.3 kg/cm2 ), go to step 15).
  13. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF  . Disconnect fuel return line from fuel rail. Attach a piece of fuel hose to return line and place in a container. Turn ignition off for about 10 seconds. Turn ignition on. Observe fuel pressure with fuel pump operating. Fuel pressure should be 41-47 psi (2.9-3.3 kg/cm2 ). If fuel pressure is as specified, go to step 23). If fuel pressure is not as specified, go to next step.
  14. Inspect fuel rail return/outlet passage for restriction. If restriction is present, go to step 24). If restriction is not present, go to step 21).
  15. If fuel pressure is not present, go to next step. If fuel pressure is present, go to step 17).
    CAUTION: DO NOT  allow fuel pressure to exceed 65 psi (4.5 kg/cm2 ).
  16. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF  . Connect Fuel Pressure Gauge (J-34730-1A). Install Fuel Pipe Shut-Off Adapter (J-37287) between fuel feed line and return line. Open valve on shut-off adapter. Using scan tool, pressurize fuel system. Bleed air out of fuel gauge. Wait for pressure to build up. Slowly close valve on fuel shut-off adapter. Fuel pressure should be 41-47 psi (2.9-3.3 kg/cm2 ). If fuel pressure increases to greater than specification, go to step 21). If fuel pressure does not increase to greater than specification, go to step 7).
  17. Check fuel system electrical circuits. See FUEL SYSTEM under NO-START DIAGNOSIS  . If fuel pump circuit is faulty, go to step 24). If fuel pump circuit is okay, go to next step.
  18. Inspect fuel filter for obstruction, fuel supply line for restriction, fuel pump strainer for correct installation, fuel pump strainer for obstructions or fuel pump flex pipe for leaks. Repair or replace as necessary. After repairs, go to step 24). If problem was not found, go to next step.
  19. Replace fuel sending unit. After repairs, go to step 25).
  20. Locate and repair vacuum leak to fuel pressure regulator. After repairs, go to step 25).
  21. Replace fuel pressure regulator. After repairs, go to step 25).
  22. Locate and replace and leaking fuel injector(s). After repairs, go to step 25).
  23. Locate and correct restriction in fuel return line. After repairs, go to step 25).
  24. Repair problem as necessary. After repairs, go to step 25).
  25. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF  . Connect Fuel Pressure Gauge (J-34730-1A) to fuel pressure connector. Turn ignition on with engine off. With fuel pump running, fuel pressure should be 41-47 psi (2.9-3.3 kg/cm2 ). If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to step 11).
  26. Wait for fuel pump to stop running. Observe fuel pressure after 10 minutes. Fuel pressure should remain within 5 psi (.35 kg/cm2 ) of specified pressure. If pressure drops more than 5 psi (.35 kg/cm2 ), go to step 10). If pressure remains within 5 psi (.35 kg/cm2 ) of specified pressure, system is okay.
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