GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Generic 🢒 2008 🢒 Unit Repair 🢒 Engine 🢒 Engine Controls and Fuel - LS Engines 🢒 Fuel Injector Balance Test with Special Tool

Diagnostic Instructions
    • Perform the Powertrain On Board Diagnostic (OBD) System Check prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provide an overview of each diagnostic category.

Diagnostic Fault Information

Fuel Injector Balance Test Example

Cylinder

1

2

3

4

First Reading

380 kPa (55 psi)

380 kPa (55 psi)

380 kPa (55 psi)

380 kPa (55 psi)

Second Reading

303 kPa (44 psi)

241 kPa (35 psi)

345 kPa (50 psi)

303 kPa (44 psi)

Amount Of Drop

62 kPa (9 psi)

138 kPa (20 psi)

34 kPa (5 psi)

62 kPa (9 psi)

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

Injector OK

Fuel Injector - Too Much Pressure Drop

Faulty Injector - Too Little Pressure Drop

Injector OK

Circuit/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.

Diagnostic Aids
    • Monitoring the misfire current counters, or misfire graph, may help to isolate the fuel injector that is causing the condition.
    • Operating the vehicle over a wide temperature range may help isolate the fuel injector that is causing the condition.
    • Perform the fuel injector balance test within the conditions of the customers concern. A fuel injector condition may only be apparent at a certain temperature, or under certain conditions.

Reference Information

Connector End View Reference

    •  Engine Control Module Connector End Views
    •  Engine Controls Connector End Views

Description and Operation

Fuel System Description

Scan Tool Reference

Engine Control Module Scan Tool Information

Special Tools Required

J 39021 Fuel Injector Coil and Balance Tester

Component Testing

Fuel Injector Balance Test with Special Tool

  1. Ignition ON, with a scan tool verify that the engine coolant temperature (ECT) is less than 94°C (201°F).
    2. ⇒If the ECT is greater than 94°C (201°F) allow the engine to cool before proceeding.
  2. Ignition OFF, install the fuel pressure gage. Refer to Fuel Pressure Gage Installation and Removal .
  3. Ignition ON, verify the fuel pressure is within 380-427 kPa (55-62 psi).
    4. ⇒If the fuel pressure is not within the specified range refer to Fuel System Diagnosis for further diagnosis of the fuel system.
  4. Monitor the fuel pressure gage for 1 minute. Verify that the fuel pressure does not drop greater than 34 kPa (5 psi).
    5. ⇒If the fuel pressure decreases greater than 34 kPa (5 psi) refer to Fuel System Diagnosis for further diagnosis of the fuel system.

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

  5. Connect the J 39021 to a fuel injector with the amperage supply selector switch on the fuel injector tester to the Balance Test 0.5-2.5 amp position.
  6. Command the fuel pump relay ON with a scan tool and record the fuel pressure indicated by the fuel pressure gage after the fuel pressure stabilizes. This is the first pressure reading.

    7. Important: 

       • Repeat this step for each fuel injector in order to obtain a pressure drop value for each fuel injector.
       • 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.

  7. Energize the fuel injector by depressing the Push to Start Test button on the fuel injector tester. Record the fuel pressure indicated by the fuel pressure gage after the fuel injector has stopped pulsing. This is the second pressure reading.
  8. Add all of the individual pressure drop values in order to calculate the total pressure drop. Divide the total pressure drop by the number of fuel injectors in order to calculate the average pressure drop. The difference between any individual pressure drop and the average pressure drop should not be greater than 20 kPa (3 psi).
    9. ⇒If the difference between any individual pressure drop and the average pressure drop is greater than 20 kPa (3 psi), replace the fuel injector.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Fuel Injector Replacement