GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2004 🢒 Ascender - 2WD 🢒 Engine 🢒 Engine Controls - 4.8L, 5.3L, and 6.0L 🢒 Fuel Injector Balance Test with Tech 2
Table 1: Fuel Injector Balance Test Example (Typical)

Description

The scan tool is first used to energize the fuel pump. The scan tool is then used to pulse each 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 the flow through each injector.

Fuel Injector Balance Test Example (Typical)

Cylinder

1

2

3

4

1st Reading

296 kPa (43 psi)

296 kPa (43 psi)

296 kPa (43 psi)

296 kPa (43 psi)

2nd Reading

131 kPa (19 psi)

117 kPa (17 psi)

124 kPa (18 psi)

145 kPa (21 psi)

Amount of Drop

165 kPa (24 psi)

179 kPa (26 psi)

172 kPa (25 psi)

151 kPa (22 psi)

Average Range: 156-176 kPa (22.5-25.5 psi)

Injector OK

Replace fuel injector - too much fuel pressure drop

Injector OK

Replace fuel injector - too little fuel pressure drop

Test Description

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

  1. 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

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module Connector End Views

1

Did you perform the Diagnostic System Check - Engine Controls?

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Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Did you perform the Fuel Injector Coil Test?

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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).

Important: Verify there is adequate fuel 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. Command the fuel pump ON with a scan tool.

    6. Important: 

       • You may need 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 fuel pressure gage, with the fuel pump commanded ON.

Is the fuel pressure within the specified value?

380-427 kPa (55-62 psi)

Go to Step 4

Go to Fuel System Diagnosis

4

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.

Observe the fuel pressure gage 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 5

5

Notice: Refer to Fuel Injector Balance Test Notice in the Preface section.

  1. Select the Fuel Injector Balance Test function with a scan tool.
  2. Select an injector to be tested.
  3. Press Enter. This will prime the fuel system.

    4. 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.

  4. Record the fuel pressure indicated by the fuel pressure gage after the fuel pressure stabilizes. This is the 1st pressure reading.
  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.

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 6

Go to Symptoms - Engine Controls

6

Perform the Fuel Injector Cleaning .

Did you complete the procedure?

--

Go to Step 7

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7

Operate the vehicle in order to verify the repair.

Does a driveability condition still exist?

--

Go to Symptoms - Engine Controls

System OK