System Diagnosis - Fuel System Pressure Test

Fuel System Pressure Test (1 Of 4):

Fuel System Pressure Test (2 Of 4):

Fuel System Pressure Test (3 Of 4):

Fuel System Pressure Test (4 Of 4):

Fuel System Pressure Test:

Circuit Description
When the ignition switch is turned on, the Powertrain Control Module (PCM) will turn on the in-tank fuel pump. The in-tank fuel pump remains on as long as the engine cranks or runs and the PCM receives reference pulses. If no reference pulses exist, the PCM will turn the in-tank fuel pump off 2 seconds after the ignition switch is turned on or 2 seconds after the engine stops running.

The in-tank fuel pump is an electric pump within an integral reservoir. The in-tank fuel pump supplies fuel through an in-line fuel filter to the fuel passage within the lower manifold assembly. The fuel pump is designed in order to provide fuel at a pressure above the pressure needed by the fuel injectors. A fuel pressure regulator, attached to the lower manifold assembly, keeps the fuel available to the fuel injectors at a regulated pressure. Unused fuel returns to the fuel tank by a separate fuel return pipe.

Test Description
The numbers below refer to the step numbers in the diagnostic table.

2. In order to relieve the fuel pressure, refer to Fuel Pressure Relief Procedure. With the ignition switch ON and the fuel pump running, the fuel pressure indicated by the fuel pressure gauge should be 284-325 kPa (41-47 psi).
3. A fuel system that cannot maintain a constant fuel pressure may have a leak in one or more of the following areas:

^ The Fuel Pump Check Valve.
^ The Fuel Pump Connecting Hose.
^ The Valve or Valve Seat within the Fuel Pressure Regulator.
^ The Fuel Injectors.

Important: Make sure the fuel system is not operating in the Fuel Cut-Off Mode. This can cause false indications by the scan tool.

4. A fuel pressure which drops off during acceleration, cruise, or a hard cornering may cause a lean condition. A lean condition can cause a loss of power, surging, or a misfire. A scan tool can diagnose a lean condition. If an extremely lean condition occurs, the Oxygen Sensors will stop toggling. The oxygen sensor output voltages will drop below 500 mV. Also the Fuel Injector Pulse Width will increase.
7. When the engine idles, the manifold pressure is low (high vacuum). This low pressure (high vacuum) is applied to the fuel pressure regulator diaphragm by the spring inside the fuel pressure regulator. When this happens, the result is lower fuel pressure. The fuel pressure at idle than the fuel pressure noted in Step 2 with the engine OFF.
11. A rich condition may result from the fuel pressure being above 325 kPa (47 psi). A rich condition may cause a DTC P0132 or a DTC P0172 to set. The driveability condition associated with rich condition can include a hard starting (followed by black smoke) and a strong sulfur smell from the exhaust.
12. This test determines if the high fuel pressure is due to a restricted fuel return pipe or if the high fuel pressure is due to a faulty fuel pressure regulator.
15. A lean condition may result from the fuel pressure being below 284 kPa (41 psi). A lean condition may cause a DTC P0131 or a DTC P0171 to set. The Driveability conditions associated with lean conditions can include hard starting (when the engine is cold), hesitation, poor driveability, lack of power, surging, and misfiring.

CAUTION: Do not allow the fuel pressure to exceed 414 kPa (60 psi). Fuel Pressure in excess of 414 kPa (60 psi) may damage the fuel pressure regulator.

16. Restricting the fuel return pipe causes the fuel pressure to rise above the regulated fuel pressure. Using a scan tool in order to pressurize the system, the fuel pressure should rise above 325 kPa (47 psi) as the gauge outlet hose is pinched.
22. Check the spark plug associated with a particular fuel injector for fouling or saturation in order to determine if that particular fuel injector is leaking.
24. The fuel pressure regulator filter screen is designed to trap any contaminants introduced during engine assembly. If the fuel pressure regulator screen is dirty, it can be removed with a small pick and discarded without potential harm to the fuel pressure regulator.