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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 584 (ENGINE CONTROLS - 3.4L (TROUBLESHOOTING & DIAGNOSIS))TROUBLESHOOTINGFUEL INJECTOR BALANCE TEST WITH TECH 2TEST DESCRIPTION
1999 GMC Forward Control 5.7 R, Automatic

Test Description

1999 GMC Forward Control 5.7 R, AutomaticSECTION Test Description
WARNING: This page is about a different car, the 2004 Pontiac Aztek and 2004 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.

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

  1. 3:  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. 6:  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.
Fuel Injector Balance Test with Tech 2

Step Action Values Yes No
1 Did you perform the Diagnostic System Check-Engine Controls? - Go to Step 2  Go to Diagnostic System Check - Engine Controls
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 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. Turn OFF all the accessories.
  3. Install the J 34730-1A  Fuel Pressure Gage and the fuel pressure gage fitting. Refer to Fuel Pressure Gage Installation and Removal .
  4. Turn ON the ignition, with the engine OFF.
  5. Command the fuel pump ON with a scan tool.
    6. 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.
  6. Observe the J 34730-1A  , with the fuel pump commanded ON.
Is the fuel pressure within the specified value?		 358-405 kPa (52-59 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 J 34730-1A  for 1 minute.Does the fuel pressure drop 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 J 34730-1A  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 J 34730-1A  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.
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?		 20 kPa (3 psi) Go to Step 7  Go to Symptoms - Engine Controls 
7 Clean the fuel injectors. Refer to Fuel Injector Cleaning Procedure .
Did you complete the action?		 - 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
RENDER: 1.0x

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.