GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 1998 🢒 Catera 🢒 Engine 🢒 Engine Controls - 3.0L 🢒 Fuel System Diagnosis

Circuit Description

The Fuel System Diagnosis determines if the fuel system is providing any fuel pressure. The following components are involved:

    • The fuel tank
    • The sending unit
    • The pump
    • The lines and the hoses
    • The pressure regulator
    • The fuel rail
    • The injectors

Also checked is the electrical operation of the fuel pump relay. This chart requires the J34730-91 Fuel Pressure Gauge.

Test Description

  1. With the ignition switch on and the fuel pump running, the fuel pressure that is indicated by the fuel pressure gauge should be 275-313 kPa (40-48 psi). This pressure is controlled by spring pressure inside of the fuel pressure regulator.

    2.

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

    A fuel system that cannot maintain a constant fuel pressure has a leak in one or more of the following areas:

    • The fuel pump check valve
    • The fuel pulse dampener
    • The valve or valve seat within the fuel pressure regulator
    • The fuel injector(s)

  1. Important: Ensure the fuel system is not operating in the Fuel Cut-Off Mode. This can cause lean indicators by the scan tool.

    A fuel pressure which drops off during acceleration, cruise, or hard cornering may cause a lean condition. A lean condition can cause a loss of power, surging, or misfire. Diagnose a lean condition using a scan tool. If an extremelylean condition occurs, the heated oxygen sensor(s) will stop toggling. The heated oxygen sensor output voltage(s) will remain below 300 mV. Also, the fuel injector pulse width will increase

  1. 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 the 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 off.

    2.

  2. A rich condition may result from the fuel pressure being above 313 kPa (48 psi). A rich condition may cause DTC P0132, DTC P0152, DTC P0172, or DTC P0175 to set. Driveability conditions associated with rich conditions can include hard starting (followed by black smoke) and a strong sulfur smell in the exhaust.

    3.

  3. This test determines if the high fuel pressure is due to a restricted fuel return line or if the high fuel pressure is due to a malfunctioning fuel pressure regulator.

    4.

  4. A lean condition may result from the fuel pressure being below 275 kPa (40 psi). A lean condition may cause DTC P0131, DTC P0151, DTC P0171, or DTC P0174 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.

    5.

  5. Notice: Do Not allow the fuel pressure to exceed 483 kPa (70 psi). Fuel pressure in excess of 483 kPa (70 psi) may damage the fuel pressure regulator.

    Restricting the fuel return line with the J 37287 fuel line shut-off adaptor causes the fuel pressure to rise above the regulated fuel pressure. With the fuel pump enabled using a scan tool, the fuel pressure should rise above 313 kPa (48 psi) as the valve on the fuel line shut-off adaptor connected to the fuel return line becomes partially closed.

  1. Check the spark plug that is 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:

    2. 1. Remove the fuel rail, but leave the fuel lines connected to the fuel rail. Refer to Fuel Injector and Fuel Rail Replacement .

    Caution: In order to reduce the risk of fire and personal injury that may result from fuel spraying on the engine, verify that the fuel rail is positioned over the fuel injector ports. Also verify that the fuel injector retaining clips are intact.

    2. Lift the fuel rail just enough in order to leave the fuel injector nozzles in the fuel injector ports.
    3. Pressurize the fuel system by using the scan tool fuel pump enable.
    4. Visually and physically inspect the fuel injector nozzles for leaks.

Fuel System Diagnosis

Step

Action

Value(s)

Yes

No

1

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Turn off the ignition.
  2. Turn off the air conditioning system.

    3. Caution: Wrap a shop towel around the fuel pressure connection in order to reduce the risk of fire and personal injury. The towel will absorb any fuel leakage that occurs during the connection of the fuel pressure gage. Place the towel in an approved container when the connection of the fuel pressure gage is complete.

  3. Install the J34730-1A fuel pressure gauge.
  4. Place the bleed hose of the fuel pressure gauge into an approved gasoline container.
  5. Crank the engine for a few seconds.
  6. Bleed the air out of the fuel pressure gauge.
  7. Crank the engine for a few seconds. Observe the fuel pressure immediately after cranking the engine.

Is the fuel pressure within the specified limits?

275-313 kPa (40-48 psi)

Go to Step 3

Go to Step 11

3

Important: The fuel pressure may vary slightly when the fuel pump stops running. After the fuel pump stops running, the fuel pressure should stabilize and remain constant.

After the fuel pump stops running, does the fuel pressure remain constant?

--

Go to Step 4

Go to Step 8

4

Is the fuel pressure suspected of dropping-off during acceleration, cruise, or hard cornering?

--

Go to Step 5

Go to Step 7

5

Visually and physically inspect the following items for a restriction:

    • The in-line fuel filter
    • The fuel feed line

Was a restriction found?

--

Go to Step 23

Go to Step 6

6
  1. Remove the fuel sender assembly. Refer to Fuel Sender Assembly Replacement .
  2. Visually and physically inspect the following items:
    3. • The fuel pump strainer for a restriction
    • The fuel pulse dampener for leaks
    • Verify the fuel pump is the correct fuel pump for this vehicle.

Was a problem found in any of these areas?

--

Go to Step 23

Go to Step 18

7

  1. Start the engine.
  2. Allow the engine to idle at the normal operating temperature.

Does the fuel pressure drop by the amount specified?

21-69 kPa (3-10 psi)

Go to Symptoms

Go to Step 8

8
  1. Disconnect the vacuum hose from the fuel pressure regulator.
  2. With the engine idling, apply 12-14 inches of vacuum to the fuel pressure regulator.

Does the fuel pressure drop by the amount specified?

21-69 kPa (3-10 psi)

Go to Step 19

Go to Step 20

9
  1. Relieve the fuel pressure. Refer to the Fuel Pressure Relief .
  2. Disconnect the fuel feed line and the fuel return line from the fuel rail.
  3. Install the J 37287 fuel line shut-off adaptors between the fuel feed line and the fuel return line and the fuel rail. Refer to the illustration associated with the circuit description.
  4. Open the valves on the fuel line shut-off adaptors.
  5. Turn off the ignition.
  6. Turn on the fuel pump with a scan tool,.
  7. Place the bleed hose of the fuel pressure gauge into an approved gasoline container.
  8. Bleed the air out of the fuel pressure gauge.
  9. Wait for the fuel pressure to build.
  10. Turn off the fuel pump with the scan tool.
  11. Close the valve in the fuel line shut-off adaptor that is connected to the fuel feed line.

Does the fuel pressure remain constant?

--

Go to Step 20

Go to Step 10

10
  1. Open the valve in the fuel line shut-off adaptor that connects to the fuel feed line.
  2. Turn on the fuel pump with a scan tool.
  3. Wait for the fuel pressure to build.
  4. Turn off the fuel pump with the scan tool.
  5. Close the valve in the fuel line shut-off adaptor that connects to the fuel return line.

Does the fuel pressure remain constant?

--

Go to Step 20

Go to Step 21

11

Is the fuel pressure above the specified limit?

407 kPa (59 psi)

Go to Step 12

Go to Step 14

12

  1. Relieve the fuel pressure. Refer to the Fuel Pressure Relief .
  2. Disconnect the fuel return line from the fuel rail.
  3. Install the J 37287 fuel line shutoff adapters between the fuel feed line and the fuel return line.
  4. Attach a length of flexible fuel hose to the fuel rail return outlet passage.
  5. Place the open end of the flexible fuel hose into an approved gasoline container.
  6. Crank the engine for a few seconds. Observe the fuel pressure immediately after cranking.

Is the fuel pressure within the specified limits?

275-313 kPa (40-48 psi)

Go to Step 22

Go to Step 13

13

Visually and physically inspect the fuel rail outlet passages for a restriction.

Was a restriction found?

--

Go to Step 23

Go to Step 20

14

Is the fuel pressure above the specified value?

0 kPa (0 psi)

Go to Step 15

Go to Step 16

15

  1. Relieve the fuel pressure. Refer to the Fuel Pressure Relief .
  2. Disconnect the fuel return line from the fuel rail. Refer to Servicing Quick Connect Fittings .
  3. Install the J 37287 fuel line shut-off adaptor between the fuel return line and the fuel rail. Refer to the illustration associated with the circuit description.
  4. Open the valve on the fuel line shut-off adaptor.
  5. Turn on the ignition.
  6. Turn on the fuel pump with a scan tool.
  7. Place the bleed hose of the fuel pressure gauge into an approved gasoline container.
  8. Bleed the air out of the fuel pressure gauge.

    9. Notice: Do Not allow the fuel pressure to exceed 483 kPa (70 psi). Fuel pressure in excess of 483 kPa (70 psi) may damage the fuel pressure regulator.

  9. Slowly close the valve in the fuel line shut-off adaptor that connects to the fuel return line.

Does the fuel pressure rise above the specified value?

407 kPa (59 psi)

Go to Step 20

Go to Step 6

16

Refer to Fuel Pump Circuit Diagnosis in order to diagnose the fuel pump electrical circuit.

Was a problem found with the fuel pump electrical circuit?

--

Go to Step 23

Go to Step 17

17

Important: Remove the fuel sender assembly in order to inspect the fuel pump strainer and the fuel pulse dampener. Refer to Fuel Sender Assembly Replacement .

Visually and physically inspect the following items:

    • The in-line fuel filter for obstructions
    • The fuel feed line for a restriction
    • The fuel pump strainer for obstructions
    • The fuel pulse dampener for leaks

Was a problem found in any of these areas?

--

Go to Step 23

Go to Step 18

18

Replace the fuel pump. Is the action complete?

--

System OK

--

19

Locate and repair the loss of vacuum to the fuel pressure regulator.

Is the action complete?

--

System OK

--

20

Replace the fuel pressure regulator and fuel rail assembly.

Is the action complete?

--

System OK

--

21

Locate and replace any of the leaking injector(s).

Is the action complete?

--

System OK

--

22

Locate and correct the restriction in the fuel return line.

Is the action complete?

--

System OK

--

23

Repair the problem as necessary.

Is the action complete?

--

System OK

--