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Test Description

The number below refers to the step number on the diagnostic table.

  1. 3:  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.
Fuel Injector Balance Test with Tech 2

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 Coil Test 
3 
IMPORTANT: DO NOT perform this test if the engine coolant temperature (ECT) is above 94°C (201°F).
Observe the ECT Sensor parameter with a scan tool.Is the ECT Sensor parameter 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 relay may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.
    • DO NOT start the engine.
  5. Command the fuel pump relay ON with a scan tool.
  6. Observe the fuel pressure gage, with the fuel pump operating.
Is the fuel pressure within the specified value?		 379-427 kPa (55-62 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
  1. Select the Fuel Injector Balance Test function with a scan tool, 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 1st 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 2nd pressure reading.
  7. Press Enter again to bring you back to the Select Injector screen.
  8. Repeat for each fuel injector.
  9. Subtract the 2nd pressure reading from the 1st 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.
Is the difference between any individual pressure drop and the average pressure drop more than the specified value?		 20 kPa (3 psi) Go to Step 7  Go to Symptoms - Engine Controls 
7 Replace the fuel injector with the largest drop below the average pressure drop. Refer to Fuel Injector Replacement (4.3L (RPO LU3) Engine) .
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 
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