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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 II (OBD-II) system check. See ON-BOARD DIAGNOSTIC (OBD-II) SYSTEM CHECK in TESTS W/CODES - INTRODUCTION article. After performing OBD-II system check, go to next step.
  2. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELEASE  . Connect Fuel Pressure Gauge Kit (J-29658-D) 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 21). 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 23). 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, 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 23). If no problems are found, go to step 20).
  8. 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 drops as specified, see TESTS W/O CODES article. If fuel pressure does not drop 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 drops specified, go to step 19). If fuel pressure does not drop as specified, go to step 20).
  10. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELEASE  . Connect fuel bleed hose to pressure gauge. Insert bleed hose into approved gasoline can. Using scan tool, pressurize fuel system. Bleed air out of fuel gauge. Wait for pressure to build up. Pinch fuel return hose. If fuel pressure remains constant, go to step 21). If fuel pressure does not remain constant, go to next step.
  11. Using scan tool, pressurize fuel system. Wait for pressure to build up. Close valve in fuel pipe shut-off adapter connected to fuel return hose. If fuel pressure remains constant, go to step 20). 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 RELEASE  . Disconnect fuel return line from fuel rail. Attach a piece of fuel hose to return line and place in an approved gasoline 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 exists, go to step 24). If restriction does not exist, go to step 20).
  15. Recheck fuel pressure. If no fuel pressure exists, go to next step. If fuel pressure exists, 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 RELEASE  . Using scan tool, pressurize fuel system. Bleed air out of fuel gauge. Wait for pressure to build up. Slowly pinch fuel pressure gauge outlet hose. Fuel pressure should be about 47 psi (3.3 kg/cm2 ). If fuel pressure increases to greater than specification, go to step 20). If fuel pressure does not increase to greater than specification, go to step 7).
  17. Check fuel system electrical circuits. See WIRING DIAGRAMS article. 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 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 step 21).
  19. Locate and repair vacuum leak to fuel pressure regulator. After repairs, system is okay.
  20. Replace fuel pressure regulator. After repairs, system is okay.
  21. Replace fuel sending unit. After repairs, system is okay.
  22. Locate and replace any leaking fuel injector(s). After repairs, system is okay.
  23. Locate and correct restriction in fuel return line. After repairs, system is okay.
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