GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC Suburban - 2WD 🢒 Engine 🢒 Engine Controls - 5.0L and 5.7L 🢒 Fuel Injector Balance Test
Table 1: Injector Balance Test Example
Table 2: Fuel Injector Balance Test Procedure

Object Number: 17713 Size: SF

Injector Balance Test Example

Cylinder

1st Reading

2nd Reading

Amount of Drop

Test Results

1

434 kPa (63 psi)

351 kPa (51 psi)

83 kPa (12 psi)

Injector OK

2

434 kPa (63 psi)

331 kPa (48 psi)

103 kPa (15 psi)

Faulty injector - too much fuel drop

3

434 kPa (63 psi)

351 kPa (51 psi)

83 kPa (12 psi)

Injector OK

4

434 kPa (63 psi)

365 kPa (53 psi)

69 kPa (10 psi)

Faulty injector - too little fuel drop

5

434 kPa (63 psi)

344 kPa (50 psi)

90 kPa (13 psi)

Injector OK

6

434 kPa (63 psi)

344 kPa (50 psi)

90 kPa (13 psi)

Injector OK

7

434 kPa (63 psi)

344 kPa (50 psi)

90 kPa (13 psi)

Injector OK

8

434 kPa (63 psi)

344 kPa (50 psi)

90 kPa (13 psi)

Injector OK

Test Results: Combine all of the injector pressure drops and divide this number by the amount of injectors available. This is the average pressure drop. Each individual injectors pressure drop value must be within 10 kPa (1.5 psi) of the average pressure drop value.

Circuit Description

The Fuel Injector Tester J 39021 , the Injector Switch Box J 39021-210 and the Injector Harness Connector J 39021-302 energize the 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. All injectors should be within the same pressure drop range, the average pressure drop value for all injectors is ±10 kPa (1.5 psi).

Test Description

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

  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. Refer to the illustration above.

Fuel Injector Balance Test Procedure

Step

Action

Value(s)

Yes

No

1

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Was the Fuel Injector Coil Test performed?

--

Go to Step 3

Go to Fuel Injector Solenoid Coil Test

3

Is the engine coolant temperature above the specified value?

94°C (201°F)

Go to Step 4

Go to Step 5

4

Allow the engine to cool below the specified value.

Is the action complete?

94°C (201°F)

Go to Step 5

--

5

  1. Turn ignition OFF.
  2. Relieve the fuel system pressure. Refer to Fuel Pressure Relief Procedure .
  3. Install the fuel pressure gauge.
  4. Turn ON the ignition leaving the engine OFF.
  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 fuel pressure gauge.
  8. Use a scan tool in order to pressurize the fuel system.
  9. Wait for the fuel pressure to build.

    10. Important: The fuel pump will run for approximately 2 seconds. Repeat Step 5 as necessary in order to achieve the highest possible fuel pressure.

  10. Observe the reading on the fuel pressure gauge.

Is the fuel pressure within the specified limits?

Central SFI - 415-455 kPa (60-66 psi)

Go to Step 6

Go to Fuel System Diagnosis

6

Turn the fuel pump OFF.

Does the fuel pressure remain constant?

--

Go to Step 7

Go to Fuel System Diagnosis

7

  1. Turn the ignition OFF.
  2. Connect the J 39021 Fuel Injector Tester , the J 39021-301 Injector Harness Connector and the J 39021-210 Injector Switch Box to the fuel meter body (L30/L31 applications use Injector Harness Connector J 39021-302, L29 use J 39021-303).
  3. Set the amperage supply selector switch on the fuel injector tester to the Balance Test 0.5-2.5 amp position.
  4. Select the injector to be tested on the Injector Switch Box.
  5. Turn ON the ignition leaving the engine OFF.
  6. Use a scan tool in order to pressurize the fuel system.
  7. Record the fuel pressure indicated by the fuel pressure gauge after the fuel pressure stabilizes. This is the 1st pressure reading.
  8. Energize the fuel injector by depressing the Push to Start Test button on the fuel injector tester.
  9. Record the fuel pressure indicated by the fuel pressure gauge after the fuel pressure gauge needle has stopped moving. This is the 2nd pressure reading.
  10. Repeat Steps 4 through 9 for each fuel injector.
  11. Subtract the 2nd pressure reading from the 1st pressure reading for one fuel injector. The result is the pressure drop value.
  12. Obtain a pressure drop value for each fuel injector.
  13. Add all of the individual pressure drop values. This is the total pressure drop.
  14. 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 8

Go to Symptoms

8

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 7.

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 9

Go to Symptoms

9

Replace the malfunctioning fuel injector(s). Refer to Central Sequential Multiport Fuel Injector Replacement

Is the action complete?

--

Go to Step 10

--

10
  1. Turn ignition OFF.
  2. Remove test equipment.
  3. Re-connect all harnesses and fuel lines.
  4. Install a scan tool.
  5. Turn ON the ignition leaving the engine OFF.
  6. Check for fuel leaks
  7. Using the scan tool, select Clear Information function.
  8. Start the engine.
  9. Idle until normal operating temperature is reached.

Are any DTCs displayed that have not been diagnosed?

--

Go to the applicable DTC table

System OK