GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 1999 🢒 Firefly (Canada) 🢒 Engine 🢒 Engine Controls - 1.3L 🢒 Fuel System Diagnosis

Object Number: 241864 Size: MF
(1)Fuel Injectors
(2)Fuel Rail
(3)Fuel Pressure Regulator
(4)Fuel Return Pipes/Hoses
(5)Fuel Tank
(6)Fuel Sender Assembly (Fuel Pump)
(7)Fuel Feed Pipes/Hoses
(8)Fuel Rail Adapter (J 34730-75)
(9)Fuel Pressure Gauge (J 34730-1A )

System Description

The powertrain control module (PCM) will energize the fuel pump relay for 2 seconds when the ignition switch is turned to the ON position. The fuel pump will operate and pressurize the fuel system when the fuel pump relay is energized. The PCM receives ignition system reference pulses when the engine is cranked or running. The PCM will continue to energize the fuel pump relay as long as the PCM receives ignition system reference pulses. The PCM will de-energize the fuel pump relay when ignition system reference pulses are no longer detected.

The fuel pump delivers fuel to the fuel injectors in the fuel rail at a controlled pressure. The controlled pressure is 270-310 kPa (38.5-44 psi) when the fuel pump is energized and the engine is not running. The controlled pressure is 200-240 kPa (28.5-34 psi) when the engine is idling at normal operating temperatures. The fuel-pressure regulator maintains the correct fuel pressure at all times by returning excess fuel to the fuel tank.

Diagnostic Aids

Incorrect fuel system pressure can result in any of the following conditions:

    • The engine cranks but will not start.
    • The engine cuts out or stalls.This may feel like an ignition malfunction.
    • A decrease in fuel economy and a decrease in power.
    • Hard starting

Check for water contamination of the fuel if the vehicle will not start in freezing weather. Ice can form in the fuel system and prevent the fuel from reaching the fuel injectors at the necessary fuel pressure and at the necessary volume.

The normal fuel pump electrical resistance is 0.8-1.5 ohms at 20°C (68°F).

An intermittent malfunction may be caused by a fault in the fuel pump electrical circuit. Inspect the wiring harness and the components for any of the following conditions:

    • Backed out terminals.
    • Incorrect mating of terminals.
    • Broken electrical connector locks.
    • Incorrectly formed terminals or damaged terminals.
    • Any faulty terminal to wire connections.
    • Physical damage to the wiring harness.
    • A broken wire inside the insulation.
    • Corrosion of electrical connections, of electrical splices, or of terminals.

Test Description

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

  1. The Powertrain OBD System Check prompts the technician to complete some basic checks, and to save the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data that was taken when the fault occurred. The scan tool saves the information for later reference.

    2.

  2. This step checks if fuel system pressure is meeting specifications.The ignition must be ON, and the fuel pump must be running. The Output Control on the scan tool can operate the fuel pump when the fuel level is more than 20 percent, and no DTCs are set.

    3.

  3. This step checks the fuel pressure after the fuel pump stops. Approximately one minute after the fuel pump stops, fuel pressure should remain steady at 200 kPa (28.5 psi). The Output Control on the scan tool can operate the fuel pump when the fuel level is more than 20 percent, and no DTCs are set.

    4.

  4. The vehicle should start and run. Adequate fuel pressure is available for the engine to operate. A vehicle that will not start may have inoperative injectors. Check the fuel injectors and the fuel injector circuitry. Refer to Fuel Injector Circuit Diagnosis .

  5. This step checks for normal fuel pressure when the engine is running. Fuel pressure that is not within the specified value indicates a possible fault in the fuel pressure regulator.

    6.

  6. This step checks for a faulty check valve in the fuel pump. The Output Control on the scan tool can operate the fuel pump when the fuel level is more than 20 percent, and no DTCs are set.

    7.

  7. This step checks for a faulty check valve in the fuel pump. Blocking the fuel feed hose between the fuel pressure gauge and the fuel pump, traps the fuel pressure.The pressure becomes trapped between the fuel pressure regulator and the blocked section of the fuel feed hose.Immediately after the fuel pump stops, block the fuel feed hose. If fuel pressure now remains above the specified value, the fault is between the blocked section and the fuel tank. The Output Control on the scan tool can operate the fuel pump when the fuel level is more than 20 percent, and no DTCs are set.

    8.

  8. This step checks for a faulty fuel pressure regulator. The Output Control on the scan tool can operate the fuel pump when the fuel level is more than 20 percent, and no DTCs are set.

    9.

  9. A fault in the fuel pump electrical circuit may be caused by low fuel pressure or by zero fuel pressure.

    10.

  10. This step checks for conditions except for a faulty fuel pump that can cause low fuel pressure. Check for any restrictions or for any blockages in the fuel feed lines and in the hoses, including those inside the fuel tank. Check the fuel pump electrical circuit for excessive resistance. Correct fuel pump operation requires correct voltage and adequate current flow.

    11.

  11. This step checks the operation of the fuel pressure regulator. The Output Control on the scan tool can operate the fuel pump when the fuel level is more than 20 percent, and no DTCs are set.

Step

Action

Value(s)

Yes

No

1

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

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2
  1. Turn OFF the ignition.
  2. Install the J 34730-1A fuel pressure gauge or an equivalent. Refer to Fuel Pressure Gage Installation and Removal .
  3. Check that the vehicle has an adequate supply of fuel.
  4. Turn ON the ignition while leaving the engine OFF.The fuel pump should run for approximately 2 seconds.

Was there any fuel pressure indicated?

--

Go to Step 3

Go to Step 13

3

  1. Turn OFF the ignition.

    2. Important: In order to obtain maximum fuel pressure, it may be necessary to cycle the ignition from ON to OFF to ON more than once.

  2. Turn ON the ignition while leaving the engine OFF.The fuel pump should run for approximately 2 seconds.
  3. Observe the fuel pressure while the fuel pump is running.

Is the fuel pressure within the specified range?

270-310 kPa (38.5-44.0 psi)

Go to Step 4

Go to Step 11

4
  1. Turn OFF the ignition.
  2. Observe the fuel pressure gauge for 1 minute after the fuel pump stops.

Does the fuel pressure hold at the specified value or above the specified value?

200 kPa (28.5 psi)

Go to Step 5

Go to Step 7

5

Start the engine.

Does the vehicle start and run?

--

Go to Step 6

Go to Fuel Injector Circuit Diagnosis

6

Run the engine to normal operating temperature.

Is the fuel pressure within the specified range?

200-240 kPa (28.5-35 psi)

System OK

Go to Step 9

7
  1. Check the fuel injectors, the fuel feed pipes, and the hoses for leaks.
  2. Repair as necessary.

Was a repair necessary?

--

Go to Step 19

Go to Step 8

8

  1. Turn ON the ignition while leaving the engine OFF.The fuel pump should run for approximately 2 seconds.
  2. Immediately after the fuel pump stops, observe the fuel pressure while blocking the fuel feed hose between the fuel pressure gauge and the fuel pump.

Does the fuel pressure hold at the specified value or above the specified value?

270 kPa (38.5 psi)

Go to Step 18

Go to Step 9

9

  1. Turn ON the ignition while leaving the engine OFF.The fuel pump should run for approximately 2 seconds.
  2. Observe the fuel pressure while blocking the fuel return hose.

Does the fuel pressure remain at the specified value or above the specified value?

270 kPa (38.5 psi)

Go to Step 17

Go to Step 10

10
  1. Check for any of the following:
    2. • Fuel injectors that are faulty or operating incorrectly. Refer to Fuel Injector Circuit Diagnosis .
    • A leaking fuel pressure regulator.
  2. Repair or replace the faulty fuel injectors or the leaking fuel-pressure regulator as necessary.

Is the action complete?

--

Go to Step 19

--

11

Is the fuel pressure less than the specified value?

270 kPa (38.5 psi)

Go to Step 12

Go to Step 15

12

Important: In order to obtain maximum fuel pressure, it may be necessary to cycle the ignition from ON to OFF to ON more than once.

  1. Turn ON the ignition while leaving the engine OFF.The fuel pump should run for approximately 2 seconds.
  2. Check the fuel pressure while blocking the fuel return hose.

Is the fuel pressure at the specified value or higher?

450 kPa (64 psi)

Go to Step 17

Go to Step 13

13

Was the diagnostic procedure performed for the fuel pump relay?

--

Go to Step 14

Go to Fuel Pump Electrical Circuit Diagnosis

14

  1. Check for any of the following conditions:
    2. • Check for a restricted fuel feed pipe, for a restricted hose, or for a restricted fuel filter.
    • Check for restrictions or for leaks in fuel feed pipes, in hoses, or in connections inside the fuel tank.
    • Inspect the entire fuel pump circuit. Verify B+ voltage at the fuel pump connector and less than 5.0 ohms of resistance to ground.
  2. Repair as necessary.

Was a repair necessary?

--

Go to Step 19

Go to Step 18

15

  1. Turn OFF the ignition.
  2. Relieve the fuel system pressure. Refer to Fuel Pressure Relief .
  3. Disconnect the fuel return hose from the fuel pressure regulator.
  4. Connect a new fuel hose to the fuel pressure regulator.
  5. Insert the other end of the new fuel hose into an approved gasoline container.
  6. Turn ON the ignition while leaving the engine OFF.

Is the fuel pressure within the specified range?

270 - 310 kPa (38.5 -44 psi)

Go to Step 16

Go to Step 17

16

Repair or replace the restricted fuel return pipe or the restricted hose.

Is the action complete?

--

Go to Step 19

--

17

Replace the fuel pressure regulator. Refer to Fuel Pressure Regulator Replacement .

Is the action complete?

--

Go to Step 19

--

18

Replace the fuel pump. Refer to Fuel Pump Replacement .

Is the action complete?

--

Go to Step 19

--

19

Operate the vehicle within the conditions under which the original symptom was noted.

Does the system now operate correctly?

--

Go to Diagnostic Aids