GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2008 🢒 SLS 🢒 Engine 🢒 Engine Controls and Fuel - 2.8L, 3.0L, 3.2L, or 3.6L 🢒 Fuel Injector Balance Test with Tech 2

Circuit Description

The scan tool first energizes the fuel pump and then the injectors 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.

Test Description

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

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

    2.

  2. The fuel pressure should be within the specified range.

  3. This step tests for an internal fuel leak. If the fuel pressure drops during this test, then an internal loss of pressure is indicated. The fuel pressure should reach a steady value.

    4.

  4. If the pressure drop value for each fuel injector is within 10 kPa (1.5 psi) of the average pressure drop value, the fuel injectors are flowing properly. Calculate the pressure drop value for each fuel injector by subtracting the second pressure reading from the first pressure reading.

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 with a 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 there is adequate fuel in the fuel tank before proceeding with this diagnostic.

  1. Turn OFF the ignition.
  2. Install the fuel pressure gage. Refer to Fuel Pressure Gage Installation and Removal .
  3. Turn ON the ignition, with the engine OFF.
  4. Command the fuel pump ON with a scan tool.

    5. Important: 

       • It may be necessary to command the fuel pump ON a few times in order to obtain the highest possible fuel pressure.
       • Do not start the engine.

  5. Observe the fuel pressure gage, with the fuel pump commanded ON.

Is the fuel pressure within the specified range?

380-410 kPa (55-60 psi)

Go to Step 5

Go to Fuel System Diagnosis

5

Important: The fuel pressure will drop when the fuel pump stops operating. After the fuel pump stops operating, the fuel pressure should stabilize and remain constant.

  1. Allow the fuel pressure to stabilize.
  2. 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

  1. With a scan tool, select the Fuel Injector Balance Test function, within the Special Functions menu.
  2. Select an injector to be tested.
  3. Press Enter. This will prime the fuel system.
  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 Pulse Injector button on the scan tool. This will energize the injector and decrease the fuel pressure.
  6. Record the fuel pressure indicated by the fuel pressure gage after the fuel injector has stopped pulsing. This is the second pressure reading.
  7. Press Enter again to bring you back to the Select Injector screen.
  8. Repeat for each fuel injector.
  9. Subtract the second pressure reading from the first pressure reading for one fuel injector. The result is the pressure drop value.
  10. Obtain a pressure drop value for each fuel injector.
  11. Add all of the individual pressure drop values. This is the total pressure drop.
  12. 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 either higher than the average pressure drop or lower than the average pressure drop by the specified value?

10 kPa (1.5 psi)

Go to Step 7

Go to Symptoms - Engine Controls

7

Replace the affected fuel injector. Refer to Fuel Injector and Fuel Rail Replacement .

Did you complete the replacement?

--

Go to Step 8

--

8

Operate the vehicle in order to verify the repair.

Does a driveability condition still exist?

--

Go to Symptoms - Engine Controls

System OK