GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2000 🢒 Firebird 🢒 Body and Accessories 🢒 Wiring Systems 🢒 Fuel System Pressure Test

Object Number: 12822 Size: MF
(1)Fuel Pressure Regulator Assembly
(2)Fuel Return Pipe
(3)Fuel Pump
(4)Fuel Pump Flex Pipe
(5)Fuel Feed Pipe
(6)Fuel Filter
(7)Fuel Pipe Shut Off Adapters J 37287
(8)Fuel Pressure Gauge J 34730-1A
(9)Fuel Rail Assembly

Circuit Description

When the ignition is turned ON, the powertrain control module (PCM) will turn ON the in-tank fuel pump. The in-tank fuel pump 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 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 (4). The in-tank fuel pump supplies fuel through the fuel feed pipe (1), and in-line fuel filter (2) to the fuel rail assembly (8). The fuel pump is designed to provide fuel at a pressure above the pressure needed by the fuel injectors (9). A fuel pressure regulator (7), attached to the fuel rail, keeps the fuel available to the fuel injectors at a regulated pressure. Unused fuel is returned to the fuel tank by a separate fuel return pipe (5). The fuel pump flex pipe (3) functions as a conduit for transporting pressurized fuel from the fuel pump to the above cover fuel feed pipe. The fuel pump flex pipe also eliminates fuel pump generated pressure pulse noise, and eliminates clamps formerly needed for rubber hoses or nylon pipes. The fuel pressure gauge J 34730-1A

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. With the ignition ON and the fuel pump running, the fuel pressure indicated by the fuel pressure gage 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.

    2.

  2. A fuel system that drops more than 5 psi in 10 minutes has a leak in one or more areas:

    3.

  3. Fuel pressure that 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. A lean condition can be diagnosed using a scan tool. If an extremely lean condition occurs, the oxygen sensorss will stop toggling. The oxygen sensor output voltages will drop below 500 mV. Also, the fuel injector 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 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.

    3.

  3. 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.

    4.

  4. 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.

    5.

  5. Restricting the fuel return pipe with the 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.

    6.

  6. 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.

Step

Action

Values

Yes

No

1

Did you preform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

    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.

  1. Relieve the fuel pressure. Refer to Fuel Pressure Relief .
  2. Turn OFF the air conditioning system.

    3. Important:: The fuel pump will run for approximately 2 seconds. Cycle the ignition as necessary in order to achieve the highest possible fuel level.

  3. Turn ON the ignition, with the engine OFF.
  4. With the fuel pump running, measure the fuel pressure indicated on the fuel pressure gauge.

Does the fuel pressure measure within the specified value?

333-376 kPa (48-55 psi)

Go to Step 3

Go to Step 12

3

The fuel pressure may vary slightly when the fuel pump stops running, the fuel pressure should stabilize and remain constant.ImportantNote the fuel pressure after the fuel pump stops running.

Does the fuel pressure drop more than the specified value in 10 minutes?

34 kPa (5 psi)

Go to Step 10

Go to Step 4

4

With the fuel pressure gauge, relieve the fuel pressure to the specified higher value.

Does the fuel pressure drop more than the specified lower value within 10 minutes?

69 kPa (10 psi)

14 kPa (2 psi)

Go to Step 19

Go to Step 5

5

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

--

Go to Step 6

Go to Step 8

6
  • Visually and physically inspect the following items for a restriction:
    • The in-line fuel filter. Refer to In-Line Fuel Filter Replacement .

Did you find and correct the condition?

--

Go to Step 24

Go to Step 7

7
  1. Remove the modular sender assembly. Refer to Fuel Sender Assembly Replacement .
  2. Visually and physically inspect the following items:
    3. • The fuel pump strainer for a restriction, correct position, and installation on the fuel sender assembly
    • The fuel pump flex pipe for leaks.
    • Verify the fuel pump is the correct fuel pump for this vehicle.

Did you find and correct the condition?

--

Go to Step 24

Go to Step 19

8

  1. Turn OFF the ignition, for 10 seconds.

    2. Important:: The fuel pump will run for approximately 2 seconds. Cycle the ignition as necessary in order to achieve the highest possible fuel level.

  2. Turn ON the ignition.
  3. Start the engine.
  4. Let the engine run to a normal operating temperature.

Does the fuel pressure measurement drop less than the specified value?

21-69 kPa (3-10 psi)

Go to Symptoms

Go to Step 9

9
  1. Disconnect the fuel pressure regulator vacuum hose.
  2. With the engine idling, apply 12-14 inches of vacuum to the fuel pressure regulator.

Does the fuel pressure measurement drop within the specified value?

21-69 kPa (3-10 psi)

Go to Step 20

Go to Step 21

10
  1. Relieve the fuel pressure. Refer to Fuel Pressure Relief
  2. Disconnect the fuel feed pipe and the fuel return pipe from the fuel rail. Refer to Metal Collar Quick Connect Fitting Service
  3. Install the J 37287 fuel pipe shut-off adapters between the fuel feed pipe and the fuel return pipe and the fuel rail.
  4. With the J 37287 fuel pipe shut-off adapters, open the valve.
  5. Turn ON the ignition, with the engine OFF.

  6. With a scan tool pressurize the fuel system.

  7. Relieve the fuel pressure. Refer to Fuel Pressure Relief
  8. With a scan tool, command the fuel pump ON.
  9. Wait for the fuel pressure to build.

    10. Notice: Do not allow the fuel pressure to exceed 450 kPa (65 psi). Fuel pressure in excess of 450 kPa (65 psi) may damage the Fuel Pressure Regulator.

  10. With the fuel pipe shut-off adapter, close the fuel feed valve.

Does the fuel pressure remain constant?

--

Go to Step 19

Go to Step 11

11
  1. With the fuel pipe shut-off adapter, open the fuel feed valve.
  2. With a scan tool, pressurize the fuel system.
  3. Wait for the fuel pressure to build.
  4. With the fuel pipe shut-off adapter, close the fuel return valve.

Does the fuel pressure remain constant?

--

Go to Step 21

Go to Step 22

12

Does the fuel pressure measure above the specified value?

376 kPa (55 psi)

Go to Step 13

Go to Step 15

13

  1. Relieve the fuel pressure. Refer to Fuel Pressure Relief
  2. Disconnect the fuel pipe shut-off adaptor, from the fuel rail return pipe. Refer to Metal Collar Quick Connect Fitting Service
  3. Attach a length of flexible fuel hose to the fuel rail return outlet passage.
  4. Place the open end of the flexible hose into an approved gasoline container.
  5. Turn OFF the ignition, for 10 seconds.
  6. Turn ON the ignition, with the engine OFF.
  7. Measure the fuel pressure with the fuel pump running.

Does the fuel pressure measure within the specified value?

333-376 kPa (48-55 psi)

Go to Step 23

Go to Step 14

14
  • Visually and physically inspect the fuel rail outlet passages for a restriction.

Did you find and correct the condition?

--

Go to Step 24

Go to Step 21

15

Does the fuel pressure measure above the specified value?

0 kPa (0 psi)

Go to Step 16

Go to Step 17

16

  1. Relieve the fuel pressure. Refer to Fuel Pressure Relief .
  2. Disconnect the fuel return pipe from the fuel rail. Refer to Metal Collar Quick Connect Fitting Service .
  3. Install the J 37287 fuel pipe shut-off adapter between the fuel return pipe and the fuel rail.
  4. With the fuel pipe shut-off adapter, open the valve.
  5. Turn ON the ignition.
  6. With a scan tool, pressurize the fuel system.
  7. Place the bleed hose of the fuel pressure gauge into an approved gasoline container.
  8. With the fuel pressure gauge, Bleed off the air.

    9. Notice: Do not allow the fuel pressure to exceed 450 kPa (65 psi). Fuel pressure in excess of 450 kPa (65 psi) may damage the Fuel Pressure Regulator.

  9. With the fuel pipe shut-off valve, slowly close the fuel return valve.

Does the fuel pressure rise above the specified value?

333-376 kPa (48-55 psi)

Go to Step 21

Go to Step 7

17

Did you find and correct the condition?

--

Go to Step 24

Go to Step 18

18
  • Visually and physically inspect the following items:
    • The in-line fuel filter for obstructions. Refer to In-Line Fuel Filter Replacement .
    • The fuel feed pipe for a restriction. Refer to Fuel Hose/Pipes Replacement - Chassis .
    • The fuel pump strainer for obstructions. Refer to Fuel Pump Strainer Replacement .
    • The fuel pump flex pipe for leaks. Refer to Fuel Sender Assembly Replacement .

Did you find and correct the condition?

--

Go to Step 24

Go to Step 19

19

Did you complete the repair?

--

Go to Step 24

--

20
  • Locate and repair the loss of vacuum to the fuel pressure regulator.

Did you complete the repair?

--

Go to Step 24

--

21

Did you complete the repair?

--

Go to Step 24

--

22

Did you complete the repair?

--

Go to Step 24

--

23
  • Locate and correct the restriction in the fuel return pipe.

Did you complete the repair?

--

Go to Step 24

--

24

    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.

  1. Relieve the fuel pressure. Refer to Fuel Pressure Relief .
  2. Turn OFF the air conditioning system.

    3. Important:: The fuel pump will run for approximately 2 seconds. Cycle the ignition as necessary in order to achieve the highest possible fuel level

  3. Turn ON the ignition, with the engine OFF.
  4. With the fuel pump running, measure the fuel pressure.

Does the fuel pressure measure within the specified value?

333-376 kPa (48-55 psi)

Go to Step 25

Go to Step 11

25

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

    when the fuel pump stops running, measure the pressure.

Does the fuel pressure drop more than the specified value in 10 minutes?

34 kPa (5 psi)

Go to Step 10

System OK