GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 GMC C Sierra - 2WD 🢒 Engine 🢒 Engine Controls - 4.3L 🢒 Fuel Injector Balance Test with Special Tool
Table 1: Fuel Injector Balance Test Example (Typical)

System Description

The scan tool is first used to energize the fuel pump relay. The fuel injector tester 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 each injector.

Fuel Injector Balance Test Example (Typical)

Cylinder

1

2

3

4

1st Reading

393 kPa (57 psi)

393 kPa (57 psi)

393 kPa (57 psi)

393 kPa (57 psi)

2nd Reading

310 kPa (45 psi)

296 kPa (43 psi)

303 kPa (44 psi)

324 kPa (47 psi)

Amount of Drop

83 kPa (12 psi)

97 kPa (14 psi)

90 kPa (13 psi)

69 kPa (10 psi)

Average Range: 75-95 kPa (10.9-13.8 psi)

Injector OK

Replace fuel injector - too much fuel pressure drop

Injector OK

Replace fuel injector - too little fuel pressure drop

Test Description

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

  1. 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.

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 Solenoid 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 range?

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

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

  1. Disconnect the multi-way harness connector of the fuel injectors.
  2. Connect the J 39021 Fuel Injector Tester, J 39021 - 210 Injector Selector Switch Box, and the J 39021-301 Injector Test Adapter to the fuel meter body.
  3. Set the amperage supply selector switch on the fuel injector tester to the Balance Test 0.5-2.5 amp position.
  4. Command the fuel pump relay ON and then OFF with a scan tool.
  5. Record the fuel pressure indicated by the fuel pressure gage after the fuel pressure stabilizes. This is the first pressure reading.

    6. Important: The fuel pressure may rise after the fuel injector stops pulsing. Record the fuel pressure value immediately after the fuel injector stops pulsing. DO NOT record the higher fuel pressure value.

  6. Energize the fuel injector by depressing the Push to Start Test button on the fuel injector tester.
  7. Record the fuel pressure indicated by the fuel pressure gage after the fuel injector has stopped pulsing. This is the second pressure reading.
  8. Repeat steps 4 through 7 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.

Is the difference between any individual pressure drop and the average pressure drop more than the specified value?

10 kPa (1.5 psi)

Go to Step 7

Go to Symptoms - Engine Controls

7

Clean the fuel injectors. Refer to Fuel Injector Cleaning .

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