GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2003 🢒 GMC C Sierra - 2WD (CNG) 🢒 Engine 🢒 Engine Controls - 6.0L 🢒 Fuel Injector Balance Test with Special Tool

Circuit Description

The J 39021 Fuel Injector Tester energizes the CNG fuel 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 fuel injector.

Test Description

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

  1. The fuel pressure should be within the specified range. Refer to Fuel System Diagnosis if the fuel pressure is not within the specified range.

    2.

  2. If the pressure drop value for each fuel injector is within 14 kPa (2.0 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.

Fuel Injector Balance Test Procedure

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check Alternative Fuels - Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Alternative Fuels (Engine Controls)

2

Did you perform the Fuel Injector Coil Test?

--

Go to Step 3

Go to Fuel Injector Solenoid Coil Test

3

  1. Start and idle the engine.
  2. Observe the fuel rail pressure sensor parameter with a scan tool.

Is the fuel pressure within the specified range?

275-345 kPa (40-50 psi

Go to Step 4

Go to Fuel System Diagnosis

4
  1. Turn OFF the ignition.
  2. Turn ON the ignition, with the engine OFF.
  3. Monitor the fuel rail pressure sensor parameter with a scan tool.

Does the fuel rail pressure remain constant?

--

Go to Step 5

Go to Fuel System Diagnosis

5

Notice: Do Not repeat any portion of this test before running the engine in order to prevent the engine from flooding.

  1. Turn OFF the ignition.
  2. Connect the J 39021 Fuel Injector Tester to a fuel injector.
  3. Set the amperage supply selector switch on the fuel injector tester to the Balance Test 0.5-2.5 amp position.
  4. Turn ON the ignition, with the engine OFF.
  5. Record the fuel pressure indicated by the fuel rail pressure sensor after the fuel pressure stabilizes. This is the first pressure reading.

    6. Important: Record the fuel pressure value immediately after the CNG fuel injector stops pulsing. The fuel pressure may rise after the fuel injector stops pulsing. Do not record the higher fuel pressure value.

  6. Energize the CNG fuel injector by depressing the Push to Start Test button on the fuel injector tester.
  7. Record the fuel pressure indicated by the fuel rail pressure sensor. This is the second fuel pressure reading.
  8. Repeat steps 1 through 6 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 more than the average pressure drop or less than the average pressure drop by the specified value?

14 kPa (2.0 psi)

Go to Step 6

Go to Symptoms - Engine Controls

6

Replace the affected CNG fuel injector. Refer to Fuel Injector Replacement .

Did you complete the replacement?

--

Go to Step 7

--

7

Operate the vehicle in order to verify the repair.

Does a driveability condition still exist?

--

Go to Symptoms - Engine Controls

System OK