Diagnostic Chart and Test Description

Diagnostic Chart A-7, Fuel System Pressure Test (Part 1 Of 2):

Diagnostic Chart A-7, Fuel System Pressure Test (Part 2 Of 2):

Fuel System Pressure Testing:

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 requirements. 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.

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 pump outlet seal.
^ Leaking valve/seat within pressure regulator.
^ Leaking injector(s).

4. A leaking injector 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 fuel rail but leave fuel lines connected.

^ Lift fuel rail out just enough to leave injector nozzles in the ports.

WARNING: 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. A drop of fuel after a minute or so does not indicate a leak problem. Injectors that drip constantly, or spray fuel are faulty, and should be cleaned or replaced.

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 in fuel cut-off mode, 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 P0131 or P0171. 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 the pump "test" terminal, 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 P0132 or P0172. Driveability conditions 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.