GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2000 🢒 Sonoma Pickup - 4WD 🢒 Engine 🢒 Engine Controls - 4.3L 🢒 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

  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 with the fuel pump running. If the fuel pressure is not within the specified range, go to Fuel System Diagnosis .

    3.

  3. Allow the fuel pressure to stabilize about 3 minutes. On a hot vehicle fuel pressure may increase due to fuel expansion after the pump stops running. This is a normal condition but the fuel pressure should stabilize and hold. The fuel pressure should reach a steady value. If the fuel pressure does not reach a steady value, refer to Fuel System Diagnosis

  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.

Fuel Injector Balance Test Procedure

Step

Action

Values

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

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Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Is the engine coolant temperature above the specified value?

94°C (201°F)

Go to Step 3

Go to Step 4

3

Allow the engine to cool below the specified value.

Is the action complete?

94°C (201°F)

Go to Step 4

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4

Caution: The fuel pump will operate for 2 seconds after you have turned off the ignition. Make sure that all the fuel pipes and fittings are securely fastened in order to prevent personal injury.

Caution: Wrap a shop towel around the fuel pressure connection in order to reduce the risk of fire and personal injury. The towel will absorb any fuel leakage that occurs during the connection of the fuel pressure gage. Place the towel in an approved container when the connection of the fuel pressure gage is complete.

  1. Turn OFF the ignition.
  2. Connect the J 34730-1A fuel pressure gauge to the fuel pressure test port.
  3. Turn ON the ignition, with the engine OFF.
  4. Install the scan tool.
  5. Energize the fuel pump using the scan tool.
  6. Place the bleed hose of the fuel pressure gauge into an approved gasoline container.
  7. Bleed the air out of the fuel pressure gauge.
  8. Again energize the fuel pump using the scan tool.
  9. Wait for the fuel pressure to build.

    10. Important: The fuel pump will run for approximately 2 seconds. Energize the fuel pump as necessary in order to achieve the highest possible fuel pressure.

  10. Observe the reading on the fuel pressure gauge while the fuel pump is running.

Is the fuel pressure within the specified range?

414-455 kPa (60-66 psi)

Go to Step 5

Go to Fuel System Diagnosis

5

After the fuel pump stops, the fuel pressure may vary slightly, then should hold steady.

Does the fuel pressure remain constant within the specified range?

379-414 kPa (55-60 psi)

Go to Step 6

Go to Fuel System Diagnosis

6

Caution: The fuel pump will operate for 2 seconds after you have turned off the ignition. Make sure that all the fuel pipes and fittings are securely fastened in order to prevent personal injury.

  1. Turn OFF the ignition.
  2. Turn ON the ignition, with the engine OFF.
  3. Select Special Functions from the scan tool menu.
  4. Select Fuel Systems.
  5. Select Injector Balance Test.
  6. Select an injector to be tested.
  7. Press enter. This will prime the fuel pump.
  8. Record the fuel pressure indicated by the fuel pressure gauge after the fuel pressure stabilizes. This is the first pressure reading.
  9. Energize the fuel injector by depressing the Pulse Injector button on the scan tool. This will energize the injector and decrease fuel pressure.
  10. Record the fuel pressure indicated by the fuel pressure gauge after the fuel pressure gauge needle has stopped moving. This is the second pressure reading.
  11. Press Enter again to bring you back to the Select Injector screen.
  12. Repeat steps 6 through 11 for each fuel injector.
  13. Subtract the second pressure reading from the first pressure reading for one fuel injector. The result is the pressure drop value.
  14. Obtain a pressure drop value for each fuel injector.
  15. Add all of the individual pressure drop values. This is the total pressure drop.
  16. 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 Fuel Injector Solenoid Coil Test

7

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

Re-test any fuel injector that does not meet the specification. Refer to the procedure in step 6.

Does any fuel injector still 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 8

Go to Fuel Injector Solenoid Coil Test

8

Replace the faulty fuel injectors. Refer to Fuel Injector Replacement .

Is the replacement complete?

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System OK

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