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FUEL SYSTEM PRESSURE TEST
1. Perform On-Board Diagnostic (OBD) System Check. See ON-BOARD DIAGNOSTIC
(OBD) SYSTEM CHECK in TESTS W/CODES - 5.0L article. After performing OBD
system check, go to next step.
2. Turn ignition off for 10 seconds with A/C off. Relieve fuel pressure. See . Connect Fuel
Pressure Gauge (J-34730-1A) to fuel pressure test port. Turn ignition on with engine off.
Fuel pump should run for 2 seconds. Bleed air out of fuel pressure gauge into container.
Turn ignition off for 10 seconds. Turn ignition on with engine off. Cycle ignition to
obtain highest fuel pressure possible. Observe fuel pressure with fuel pump running. Fuel
pressure should be 60-66 psi (4.2-4.6 kg/cm2 ) on CSI fuel system and 56-62 psi (4.0-4.4
kg/cm2 ) on SFI fuel system. If fuel pressure is as specified, go to next step. If fuel
pressure is not as specified, go to step 8).
3. Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Fuel
pump should run for 2 seconds. Observe fuel pressure after fuel pump stops running.
After fuel pump stops, fuel pressure should stabilize and remain constant. If pressure is
within specification and holds, go to step 5). If pressure is not within specification, or is
within specification but does not hold, go to next step.
4. Relieve fuel pressure. See . Disconnect fuel filter. Drain any remaining fuel from fuel
pipes into container. Install Fuel Line Shutoff Valve (J-42873-1) in place of fuel filter.
Open valve on shutoff valve. Turn ignition off for 10 seconds with A/C off. Turn ignition
on with engine off. Check for leaks at shutoff valve. Start engine and idle for 30 seconds.
Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Wait for
fuel pressure to build. Close valve on shutoff valve. Fuel pressure should be as specified
and remain constant. If pressure is as specified and holds, go to step 12). If pressure is not
as specified, or is as specified but does not hold, go to step 6).
5. If fuel pressure is suspected of decreasing during acceleration, cruise or hard cornering,
go to step 27). If fuel pressure is not suspected of decreasing during acceleration, cruise
or hard corning, go to step 26).
6. Check fuel feed line between shutoff valve and fuel pipes. If fuel feed line is faulty, go to
step 25). If fuel feed line is okay, go to next step.
7. Open valve on shutoff valve. Relieve fuel pressure. See . Disconnect fuel return pipe
union located near fuel filter. Drain remaining fuel from fuel pipes into container. Install
Fuel Line Shutoff Valve (J-42873-2) in place of fuel return pipe union. Open valve on
shutoff valve. Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine
off. Check for leaks at fuel shutoff valve fittings. Start engine and idle for 30 seconds.
Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Wait for
fuel pressure to build. Close valve on shutoff valve installed on fuel return pipe. If fuel
pressure remains constant, go to step 22). If fuel pressure does not remain constant, go to
step 29).
8. Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Fuel
pump should run for 2 seconds, and then turn off. Observe fuel pressure after fuel pump
stops running. If fuel pressure is present, go to step 13). If fuel pressure os not present, go
to next step.
9. Turn ignition off. Connect a fused jumper wire between battery voltage and fuel pump
test terminal. Listen for operation of fuel pump. If fuel pump operates, go to next step. If
fuel pump does not operate, see FUEL SYSTEM ELECTRICAL CIRCUIT under TESTS
W/CODES - 5.0L.
10. Check for plugged fuel filter, plugged fuel pump strainer or restricted fuel line. If a
problem is found, go to next step. If a problem is not found, go to step 12).
11. Repair or replace as necessary. After repairs, go to step 30).
12. Replace fuel sending unit assembly. After replacing fuel sending unit assembly, go to
step 30).
13. Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Fuel
pump should run for 2 seconds. Observe fuel pressure. If fuel pressure is greater than 66
psi (4.6 kg/cm2 ) on CSI fuel system or 62 psi (4.4 kg/cm2 ) on SFI fuel system, go to
next step. If fuel pressure is not greater than specified, go to step 15).
14. Relieve fuel pressure. See . Disconnect engine compartment fuel return line. Attach a
flexible hose to fuel return line. Place other end of hose in container. Observe fuel
pressure within 2 seconds after ignition is turned on. Fuel pressure should be 60-66 psi
(4.2-4.6 kg/cm2 ) on CSI fuel system and 56-62 psi (4.0-4.4 kg/cm2 ) on SFI fuel system.
If fuel pressure is as specified, go to step 16). If fuel pressure is not as specified, go to
step 17).
15. Turn ignition off for 10 seconds with A/C off. Turn ignition on with engine off. Fuel
pump should run for 2 seconds. Observe fuel pressure. If fuel pressure is less than 60 psi
(4.2 kg/cm2 ) on CSI fuel system or 56 psi (4.0 kg/cm2 ) on SFI fuel system, go to step
19). If fuel pressure is not less than specified, go to step 30).
16. Locate and repair restriction in fuel return line. After repairs, go to step 30). If fuel return
line is not restricted, go to next step.
17. Check for restriction in engine fuel return outlet pipe at point where fuel line was
disconnected. If fuel return pipe is restricted, go to next step. If fuel return pipe is not
restricted, go to step 22).
18. Replace engine fuel pipes. After replacing engine fuel pipes, go to step 30).
19. Inspect in-line fuel filter and fuel line for restriction. If restriction is found, go to next
step. If restriction is not found, go to step 21).
20. Repair or replace in-line fuel filter and fuel line. After repairs, go to step 30).
21. Relieve fuel pressure. See . Disconnect fuel return pipe union located near fuel filter.
Drain remaining fuel from fuel pipes into container. Install Fuel Line Shutoff Valve (J42873-2) in place of fuel return pipe union. Open valve on shutoff valve. Turn ignition
off for 10 seconds with A/C off. Turn ignition on with engine off. Bleed air out of fuel
pressure gauge into container. Connect a fused jumper wire between battery voltage and
fuel pump test terminal. DO NOT allow fuel pressure to exceed 75 psi (4.5 kg/cm2 ).
Excess pressure may damage fuel pressure regulator. Slowly close valve on shutoff valve
installed on fuel return pipe. Fuel pressure should increase to greater than 66 psi (4.6
kg/cm2 ) on CSI fuel system or 62 psi (4.4 kg/cm2 ) on SFI fuel system. If fuel pressure
increases as specified, go to next step. If fuel pressure does not increase as specified, go
to step 23).
22. Replace fuel pressure regulator. After replacing fuel pressure regulator, go to step 30).
23. Check for the following conditions:
o Low fuel pump voltage due to high resistance connections.
o High fuel pump voltage due to internal pump binding.
o Poor fuel pump ground.
o Partially restricted fuel pump strainer.
o Incorrect or faulty fuel pump.
If any of the listed conditions are present, go to next step. If none of the listed conditions
are present, go to step 12).
24. Repair or replace as necessary. After repairs, go to step 30).
25. Replace fuel feed line. After repairs, go to step 30).
26. Start engine. Allow engine to idle until normal operating temperature is reached. Open
throttle quickly. Observe fuel pressure. Fuel pressure should increase to near 66 psi (4.6
kg/cm2 ) on CSI fuel system or 62 psi (4.4 kg/cm2 ) on SFI fuel system. If fuel pressure
increases quickly, see TESTS W/O CODES - 5.0L article. If fuel pressure does not
increase quickly, go to next step.
27. Check for the following conditions:
o In-line fuel filter for restriction.
o Fuel feed pipe for restriction.
o Mispositioned or damaged fuel pump strainer.
o Fuel pump flex pipe for leaks.
o Vehicle is equipped with correct fuel pump.
o Fuel pump electrical wiring for high resistance.
If any of the listed conditions are present, go to next step. If none of the listed conditions
are present, go to step 12).
28. Repair or replace as necessary. After repairs, go to step 30).
29. Locate and replace any leaking injector(s). After replacing leaking injector(s), go to next
step. If all injectors are okay, go to FUEL INJECTOR BALANCE TEST under FUEL
SYSTEM in SYSTEM/COMPONENT TESTS - 5.0L article.
30. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If additional DTC(s)
is present, diagnose DTC(s). See TESTS W/CODES - 5.0L article. If DTC(s) is not
present, system is okay.