Fuel Pressure: Testing and Inspection

Fuel System Pressure Test:

Fuel System Pressure Test (continued):

Fuel System Pressure Test (continued):

Fuel System Pressure Test (continued):

Engine Control (Fuel Pump And Relay):

The Fuel Pressure Check determines if the fuel system is providing fuel pressure. The components involved include the fuel tank, sending unit, pump, pipes and hoses, pressure regulator, fuel rail, and injectors. Also checked is the electrical operation of the fuel pump relay. This chart requires J 34730 Intake Air (IA) Fuel Pressure Gauge.


Test Description

Number(s) below refer to the step number(s) on the Diagnostic Chart.

2. With the ignition switch ON and the fuel pump running, the fuel pressure indicated by the fuel pressure gauge should be 333-376 kPa (48-55 psi). This pressure is controlled by the amount of pressure the spring inside the fuel pressure regulator can provide.

3. A fuel system that can not maintain a constant fuel pressure has a leak in one or more of the following areas:

^ The Fuel Pump Check Valve.

^ The Fuel Pump Flex Pipe.

^ The Fuel Pressure Regulator.

^ The Fuel Injector(s).

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

7. When the engine is at idle, the manifold pressure is low (high vacuum). This low pressure (high vacuum) is applied to the fuel pressure regulator diaphragm. The low pressure (high vacuum) will offset the pressure being applied to the fuel pressure regulator diaphragm by the spring inside fuel pressure regulator. When this happens, the result is lower fuel pressure. The fuel pressure at idle will vary slightly as the barometric pressure changes, but the fuel pressure at idle should always be less than the fuel pressure noted in Step 2 with the Engine not running.

11. A rich condition may result from the fuel pressure being above 376 kPa (55 psi). 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.

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 333 kPa (48 psi). 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 the engine is cold), hesitation, poor driveability, lack of power, surging, and misfiring.

Notice: Do not let the fuel pressure exceed 414 kPa (60 psi), as damage to the fuel pressure regulator may result.

16. Restricting the Fuel Return Pipe with the J 37287 Fuel Pipe Shut-Off Adapter causes the fuel pressure to rise above the regulated fuel pressure. Using a scan tool to pressurize the system, the fuel pressure should rise above 376 kPa (55 psi) as the valve on the Fuel Pipe Shut-Off Adapter connected to the Fuel Return Pipe becomes partially closed.

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. If checking the spark plug associated with a particular fuel injector for fouling or saturation does not determine that a particular fuel Injector is leaking, use the following procedure: