GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2000 🢒 Firefly (Canada) 🢒 Engine 🢒 Engine Controls - 1.0L 🢒 Fuel System Diagnosis

Object Number: 187150 Size: SF
(1)Throttle Body Fuel Injection Unit
(2)Fuel Injector
(3)Fuel Tank
(4)Fuel Pump
(5)Fuel Feed and Fuel Return Pipes
(6)Fuel Pressure Gauge (J 34730-1)
(7)Fuel Rail Adapter (J 34730-75)
(8)Fuel Pressure Regulator

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 pressurizes the fuel system when the fuel pump relay is energized. The PCM receives ignition system reference pulses if the engine is being cranked or if the engine is 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 if the ignition system reference pulses are no longer detected.

The fuel pump will deliver fuel to the fuel injector in the TBI unit at a controlled pressure. The controlled pressure is 160-210 kPa (23-31 psi) when the fuel pump is energized and the engine is not running. The controlled pressure is 90-140 kPa (13-20 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 loss of 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 required pressure and 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 problem 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
    • Faulty terminal-to-wire connections
    • Physical damage to the wiring harness
    • A broken wire inside the insulation
    • Corrosion of electrical connections, of splices, or of terminals

Test Description

The numbers below refer to the step numbers in the Diagnostic Table.

  1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

    2.

  2. This step checks to see if fuel system pressure is within specifications with the ignition ON, and the fuel pump running.

    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 90 kPa (13 psi).

    4.

  4. This step checks for a faulty check valve in the fuel pump.

    5.

  5. This step checks for a faulty fuel pressure regulator.

    6.

  6. This step checks for a faulty fuel pressure regulator.

    7.

  7. This step checks the operation of the fuel pressure regulator.

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic 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. Turn ON the ignition, 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 10

3

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

  1. Turn OFF the ignition.
  2. Turn ON the ignition, leaving the engine OFF (the fuel pump should run for approximately 2 seconds).
  3. Observe the fuel pressure with the fuel pump running.

Is the fuel pressure indicated within the specified values?

160- 207 kPa (23- 31 psi)

Go to Step 4

Go to Step 9

4

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

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

90 kPa (13 psi)

Go to Diagnostic Aids

Go to Step 5

5
  1. Check the fuel injector and the fuel feed pipes and hoses for leaks.
  2. Repair as necessary.

Was a repair necessary?

--

Go to Step 18

Go to Step 6

6

  1. Turn ON the ignition, leaving the engine OFF (the fuel pump should run for approximately 2 seconds).
  2. Check the fuel pressure while blocking (pinching) the fuel feed hose before the fuel pressure gauge.

Did the fuel pressure hold at the specified value?

160 kPa (23 psi)

Go to Step 17

Go to Step 7

7

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

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

160 kPa 23 (psi)

Go to Step 16

Go to Step 8

8
  1. Check for a leaking fuel injector, fuel pressure regulator or throttle body assembly.
  2. Repair or replace as necessary.

Is the action complete?

--

Go to Step 18

--

9

Is the fuel pressure below the specified value?

160 kPa (23 psi)

Go to Step 10

Go to Step 13

10

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

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

Is the fuel pressure at the specified value or higher?

310 kPa (45 psi)

Go to Step 16

Go to Step 11

11
  1. Check for a restricted fuel feed pipe or fuel filter.
  2. Repair as necessary.

Was a repair necessary?

--

Go to Step 18

Go to Step 12

12
  1. Check for any of the following conditions:
    2. • Check for leaks or restrictions in the hoses and connections to the fuel pump in the fuel tank.
    • Inspect entire fuel pump circuit. Verify B+ voltage at fuel pump connector and less than 5.0 ohms of resistance to ground.
  2. Repair as necessary.

Was a repair necessary?

--

Go to Step 18

Go to Step 17

13

Is the fuel pressure above the specified value?

207 kPa (31 psi)

Go to Step 14

--

14

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

Is the fuel pressure within the specified value?

160- 207 kPa (23- 31 psi)

Go to Step 15

Go to Step 16

15

Repair/replace the restricted fuel return pipe or hose.

Is the action complete?

--

Go to Step 18

--

16

The fuel pressure regulator is faulty. Replace the throttle body fuel injection unit upper assembly. Refer to Throttle Body Assembly Overhaul .

Is the action complete?

--

Go to Step 18

--

17

Replace the fuel pump. Refer to Fuel Pump Replacement .

Is the action complete?

--

Go to Step 18

--

18

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

Does the system now operate properly?

--

System OK

Go to Diagnostic Aids