Test Description

Numbers below refer to step numbers in Testing Procedure:

1. 2
   
   Connect fuel pressure gauge to fuel feed line as outlined in FUEL PUMP PRESSURE TEST  . Wrap a shop towel around fuel pressure connection to absorb any fuel leakage that may occur when installing fuel pressure gauge. With ignition switch on and fuel pump running, fuel pressure indicated by fuel pressure gauge should be 48-55 psi (333-376 kPa). This pressure is controlled by amount of pressure spring inside fuel pressure regulator can provide.
2. 3
   
   Fuel system that cannot maintain a constant fuel pressure has a leak in one or more of following areas:
   • Fuel pump check valve.
   • Fuel pump flex line.
   • Valve or valve seat within fuel pressure regulator.
   • Fuel injector(s).
WARNING: Ensure fuel system is not operating in Fuel Cut-Off Mode.
3. 4
   Fuel pressure that drops off during acceleration, cruise, or hard cornering may case a lean condition. A lean condition can cause a loss of power, surging, or misfire. A lean condition can be diagnosed using a Tech 2 or equivalent scan tool. If an extremely lean condition occurs, the oxygen sensor(s) will stop toggling. Oxygen sensor output voltage(s) will drop below 500 mV. Also, fuel injector pulse width will increase. When engine is at idle, manifold pressure is low (high vacuum). This low pressure (high vacuum) is applied to fuel pressure regulator diaphragm. Low pressure (high vacuum) will offset pressure being applied to fuel pressure regulator diaphragm by spring inside fuel pressure regulator. When this happens, result is lower fuel pressure. Fuel pressure at idle will vary slightly as the barometric pressure changes, but fuel pressure at idle should always be less than fuel pressure noted in step  2 with engine off.
4. 16
   
   Check spark plug associated with a particular fuel injector for fouling or saturation to determine if that particular fuel injector is leaking. If checking spark plug associated with a particular fuel injector for fouling or saturation does not determine that a particular fuel injector is leaking, use following procedure:
   • Remove fuel rail, but leave fuel lines and injectors connected to fuel rail.
   CAUTION: Reduce risk of fire and personal injury that may result from fuel spraying on the engine, by verify that fuel rail is positioned over the fuel injector ports and verify that fuel injector retaining clips are intact.
   • Lift fuel rail just enough to leave fuel injector nozzles in fuel injector ports.
   • Pressurize fuel system by connecting a 10 amp fused jumper between battery voltage and fuel pump relay connector.
   • Visually and physically inspect fuel injector nozzles for leaks.
5. 17
   
   A rich condition may result from fuel pressure being above 55 psi (376 kPa). A rich condition may cause a DTC P0132 or a DTC P0172 to set. Driveability conditions associated with rich conditions can include hard starting (followed by black smoke) and a strong sulfur smell in the exhaust.
6. 20
   
   This test determines if high fuel pressure is due to a restricted fuel return line or if high fuel pressure is due to a faulty fuel pressure regulator.
7. 21
   
   A lean condition may result from fuel pressure below 48 psi (333 kPa). A lean condition may cause a DTC P0131 or a DTC P0171 to set. Driveability conditions associated with lean conditions can include hard starting (when engine is cold), hesitation, poor driveability, lack of power, surging, and misfiring.
NOTE: Do not allow fuel pressure to exceed 60 psi (414 kPa). Fuel pressure in excess of 60 psi (414 kPa) may damage fuel pressure regulator.
8. 22
   Restricting fuel return line causes fuel pressure to rise above regulated fuel pressure. Using scan tool command fuel pump On. Fuel pressure should rise above 55 psi (376 kPa) as fuel return line is pinched with pliers.