GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2005 🢒 Grand Prix 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 Fuel Injector Balance Test with Special Tool
Table 1: Fuel Injector Balance Test Example (Actual Results May Vary)

Object Number: 17713 Size: SF
(1)First Fuel Pressure Gage Reading
(2)Second Fuel Pressure Gage Reading

System Description

The scan tool is first used to energize the fuel pump relay. The fuel injector tester is then used to pulse each injector for a precise amount of time, allowing a measured amount of fuel into the manifold. This causes a drop in system fuel pressure that can be recorded and used to compare each injector.

Fuel Injector Balance Test Example (Actual Results May Vary)

Cylinder

1

2

3

4

1st Reading

379 kPa (55 psi)

379 kPa (55 psi)

379 kPa (55 psi)

379 kPa (55 psi)

2nd Reading

280 kPa (41 psi)

310 kPa (45 psi)

340 kPa (49 psi)

317 kPa (46 psi)

Amount of Drop

99 kPa (14 psi)

69 kPa (10 psi)

39 kPa (6 psi)

62 kPa (9 psi)

Average Range: 47-87 kPa (6.8-12.6 psi)

Replace fuel injector - too much fuel pressure drop

Injector OK

Replace fuel injector - too little fuel pressure drop

Injector OK

Test Description

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

  1. The engine coolant temperature (ECT) must be below the operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.

    2.

  2. If the pressure drop value for each fuel injector is within 20 kPa (3 psi) of the average pressure drop value, the fuel injectors are flowing properly.

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Did you perform the fuel injector coil test?

--

Go to Step 3

Go to Fuel Injector Solenoid Coil Test

3

Important : DO NOT perform this test if the engine coolant temperature (ECT) is above 94°C (201°F).

Observe the ECT parameter on the scan tool.

Does the scan tool indicate that the ECT parameter is less than the specified value?

94°C (201°F)

Go to Step 4

--

4

Important: Verify that adequate fuel is in the fuel tank before proceeding with this diagnostic.

  1. Turn OFF the ignition.
  2. Turn OFF all accessories.
  3. Install the fuel pressure gage. Refer to Fuel Pressure Gage Installation and Removal .
  4. Turn ON the ignition, with the engine OFF.

    5. Important: 

       • The fuel pump may need to be commanded ON a few times to obtain the highest possible fuel pressure.
       • DO NOT start the engine.

  5. Command the fuel pump ON with a scan tool.
  6. Observe the fuel pressure gage, with the fuel pump commanded ON.

Is the fuel pressure within the specified range?

384-425 kPa (56-62 psi)

Go to Step 5

Go to Fuel System Diagnosis

5

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

Monitor the fuel pressure gage for 1 minute.

Does the fuel pressure decrease by more than the specified value?

34 kPa (5 psi)

Go to Fuel System Diagnosis

Go to Step 6

6

Important: For non-supercharged vehicles, use the J 39021-380 Injector Tester Adapter.

  1. Connect the J 39021 Fuel Injector Coil and Balance Tester.
  2. Set the amperage supply selector switch on the fuel injector tester to the Balance Test 0.5-2.5 amp position.
  3. Command the fuel pump ON and then OFF with a scan tool.
  4. Record the fuel pressure indicated by the fuel pressure gage after the fuel pressure stabilizes. This is the first pressure reading.

    5. Important: Record the fuel pressure value immediately after the fuel injector stops pulsing. The fuel pressure may rise after the fuel injector stops pulsing. DO NOT record the higher fuel pressure value.

  5. Energize the fuel injector by depressing the Push to Start Test button on the fuel injector tester.
  6. Record the fuel pressure indicated by the fuel pressure gage after the fuel injector stops pulsing. This is the second pressure reading.
  7. Repeat steps 1-6 for each fuel injector.
  8. Subtract the second pressure reading from the first pressure reading for one fuel injector. The result is the pressure drop value.
  9. Obtain a pressure drop value for each fuel injector.
  10. Add all of the individual pressure drop values. This is the total pressure drop.
  11. Divide the total pressure drop by the number of fuel injectors. This is the average pressure drop.

Does any fuel injector have a pressure drop value that is more than the average pressure drop or less than the average pressure drop by the specified value?

20 kPa (3 psi)

Go to Step 7

Go to Symptoms - Engine Controls

7

Clean the fuel injectors. Refer to Fuel Injector Cleaning .

Did you complete the action?

--

Go to Step 8

--

8

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Symptoms - Engine Controls