Fuel Pressure: Testing and Inspection

Chart A-7 Fuel System Diagnosis, 1 Of 3:

Chart A-7 Fuel System Diagnosis, 2 Of 3:

Fuel System Diagnosis:

SYSTEM DESCRIPTION
When the ignition switch is turned "ON," the Powertrain Control Module (PCM) will turn "ON" the in-tank fuel pump. It will remain "ON" as long as the engine is cranking or running, and the PCM is receiving reference pulses. If there are no reference pulses, the PCM will shut "OFF" the fuel pump within 2 seconds after ignition "ON" or engine stops.

An electric fuel pump, attached to the fuel sender assembly (inside the fuel tank), supplies fuel through an in-line filter to the fuel rail assembly. The pump is designed to provide sufficient fuel flow for all engine demands. A pressure regulator attached to the fuel rail, keeps fuel available to the injectors at a regulated pressure. Unused fuel is returned to the fuel tank by a separate line.

The fuel pump "test" connector is located on the drivers side of the engine compartment.

CHART TEST DESCRIPTION: Number(s) below refer to circled number(s) on the diagnostic chart.
1. Connect fuel pressure gage as shown in illustration. Wrap a shop towel around the fuel pressure connection to absorb any small amount of fuel leakage that may occur when installing the gage. With ignition "ON" and fuel pump running, pressure should be 284-325 kPa (41-47 psi). This pressure is controlled by spring pressure within the regulator assembly.
2. When the engine is idling, manifold pressure is low (high vacuum) and is applied to the pressure regulator diaphragm. Vacuum will offset spring pressure and result in lower fuel pressure. Fuel pressure at idle will vary somewhat depending on barometric pressure but, should be less than pressure noted in Step (1).
3. A system that does not hold pressure is caused by one of the following:
^ Leaking fuel pump check ball.
^ Leaking fuel pulse dampener.
^ Leaking valve/seat within pressure regulator.
^ Leaking injectors(s).

4. A leaking injector sticking can best be determined by checking for a fouled or saturated spark plug(s). If a leaking injector can not be determined by a fouled or saturated spark plug, the following procedure should be used:
^ Remove intake plenum.
^ Remove fuel rail but leave fuel lines connected.
^ Lift fuel rail out just enough to leave injector nozzles in the ports.

CAUTION: To reduce the risk of fire and personal injury that may result from fuel spray on the engine, make sure fuel rail is positioned over injector ports and injector retaining clips are intact.

^ Pressurize the fuel system and observe injector nozzles.

5. Fuel pressure that drops off during acceleration, cruise or hard cornering may cause a lean condition and result in a loss of power, surging or misfire. This condition can be diagnosed using a Tech 1 scan tool. If the fuel system is very lean, the HO2S will stop toggling and output voltage will drop below 500 mV. Also, injector pulse width will increase.

NOTE: Make sure system is not operating at "Fuel-Cutoff" which may cause false readings on the scan tool.

6. Fuel pressure below 284 kPa (41 psi) may cause a lean condition and may set a DTC 44. Driveability conditions can include hard starting cold, hesitation, poor driveability, lack of power, surging or misfire.
7. Restricting fuel flow in the fuel return line as directed causes fuel pressure to build above regulated pressure. With battery voltage applied to the pump "test" connector, pressure should rise above 325 kPa (47 psi) as the valve in the return line is partially closed.

NOTE: Do not allow pressure to exceed 414 kPa (60 psi) as damage to the regulator may result.

8. Fuel pressure above 325 kPa (47 psi) may cause a rich condition and may set a DTC 45. A driveability condition can include hard starting (followed by black smoke) and a strong sulphur smell in the exhaust.
9. This test determines if the high fuel pressure is due to a restricted fuel return line or a faulty fuel pressure regulator.
10. The pressure regulator filter screen is designed to trap any contaminants introduced during engine assembly. If dirty, it can be removed with a small pick and discarded without potential harm to the regulator.

FUEL SYSTEM PRESSURE RELIEF PROCEDURE

WARNING: To reduce the risk of fire and personal injury, relieve fuel system pressure before disconnecting fuel line fittings.

After relieving system pressure, a small amount of fuel may be released when disconnecting fuel line fittings. In order to reduce the chance of personal injury, cover fuel line fittings with a shop towel before disconnecting, to catch any fuel that may leak out. Place the towel in an approved container when disconnect is completed.

Tool Required:
^ J 34730-1 Fuel Pressure Gage

Procedure
1. Ignition "OFF."
2. Disconnect negative battery cable to avoid possible fuel discharge if an accidental attempt is made to start the engine.
3. Loosen fuel filler cap to relieve tank vapor pressure.
4. Connect gage J 34730-1 to fuel pressure connection. Wrap a shop towel around fitting while connecting gage to avoid spillage.
5. Install bleed hose into an approved container and open valve to bleed system pressure. Fuel line fittings are now safe for servicing.
6. Drain any fuel remaining in gage into an approved gasoline container.
7. Perform service required.
8. Tighten fuel filler cap.
9. Ignition "OFF."
10. Connect negative battery cable.
11. Cycle ignition "ON" and "OFF" twice, waiting ten seconds between cycles, then check for fuel leaks.

SERVICING QUICK-CONNECT FITTINGS

CAUTION: In order to install fuel system diagnostic equipment on vehicles equipped with plastic quick-connect fittings, fuel line separator tools must be used to disconnect the fittings. Using the separator tools to release the fittings will cause the plastic retainer to remain inside the female connector allowing diagnostic equipment to be connected.

Tools Required:
J 37088-A tool set, fuel line quick-connect separator;
J 39504 tool set, fuel line quick-connect separator (restricted access).

Remove or Disconnect
1. Relieve fuel system pressure.
2. If equipped, slide dust cover back to access quick-connect fitting.
3. Grasp both sides of fitting. Twist female connector 1/4 turn in each direction to loosen any dirt within fitting

CAUTION: Safety glasses must be worn when using compressed air, as flying dirt particles may cause eye injury.

4. Using compressed air, blow dirt out of fitting.
5. Choose correct tool from J 37088-A or J 39504 tool set for size of fitting. Insert tool into female connector, then push/pull inward to release locking tabs.
6. Pull connection apart.

Clean and Inspect

NOTE: If it is necessary to remove rust or burrs from fuel pipe, use emery cloth in a radial motion with the pipe end to prevent damage to O-ring sealing surface.

^ Using a clean shop towel, wipe off male pipe end.
^ Inspect both ends of fitting for dirt and burrs. Clean or replace components/assemblies as required.

Install or Connect

WARNING: To Reduce the Risk of Fire and Personal Injury, before connecting fitting, always apply a few drops of clean engine oil to the male pipe end of engine fuel pipe, pressure gage adapter or fuel line shut-off adapter. This will ensure proper reconnection and prevent a possible fuel leak. (During normal operation, the O-rings located in the female connector will swell and may prevent proper reconnection if not lubricated.)

1. Apply a few drops of clean engine oil to the male pipe end of engine fuel pipe, pressure gage adapter or fuel line shut-off adapter.
2. Push both sides of fitting together to cause the retaining tabs/fingers to snap into place.
3. Once installed, pull on both sides of fitting to make sure connection is secure.
4. If equipped, reposition dust cover over quick-connect fitting.