• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Two methods of testing fuel injector balance are available, the Active Fuel Injector Tester (AFIT) or a scan tool. The Active Fuel Injector Tester and SIDI adaptor connects to the engine control module harness connectors to test the high pressure fuel pump performance, fuel injector wiring, and fuel injector operation. The AFIT displays step by step instructions to precisely determine pressure drop of each fuel injector. The scan tool fuel injector balance test is performed while the engine is running at idle. The scan tool pressurizes the fuel rail to a predetermined pressure before each fuel injector is pulsed for a precise amount of time allowing a measured amount of the fuel to be injected. This causes a drop in the system fuel pressure that is recorded and used to compare each fuel injector.

• Monitoring the Current Misfire Counters 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.

Engine Controls Schematics

Component Connector End Views

Fuel System Description

Control Module References for scan tool information

• CH-47976 Active Fuel Injector Tester
• CH-47976-500A Active Fuel Injection Tester (AFIT) SIDI Adapter Kit

For equivalent regional tools, refer to Special Tools

1. Ignition ON.
2. Verify the scan tool Fuel Remaining parameter is greater than 10%.
• If the Fuel Remaining parameter is less than 10%, add fuel to the fuel tank.
• If the Fuel Remaining parameter is 10% or greater
3. Verify the scan tool ECT Sensor parameter is less than 60°C (140°F).
• If the ECT Sensor parameter is greater than 60°C (140°F), allow the engine temperature to cool.
• If the ECT Sensor parameter is 60°C (140°F) or less
4. Verify the battery is fully charged and all accessories are Off.
• If the battery is not fully charged, charge or repair battery as necessary.
• If the battery is fully charged
5. Preform the appropriate Fuel Injector Balance Test in Circuit System Testing.

Note: The CH-47976-500A Active Fuel Injection Tester (AFIT) SIDI Adapter Kit includes the following: the DMU, the CH-47976–501 SIDI Adapter Cable G1, and the CH-47976–502A SIDI Adapter Cable G2A. After the vehicle information is entered into the AFIT tool, the AFIT displays the correct adapter cable needed for that application.

1. Ignition OFF, all vehicle systems OFF. Install the CH-47976 Active Fuel Injector Tester and the CH-47976-500A Active Fuel Injection Tester (AFIT) SIDI Adapter Kit, refer to the Active Fuel Injector Tester User Guide. It may take up to 2 minutes for all vehicle systems to power down.
2. Turn ON the Active Fuel Injector Tester and select the vehicle.
3. Ignition ON, perform the Injector Test with the Active Fuel Injector Tester.
• If the Active Fuel Injector Tester aborts testing due to fuel pressure or fuel leak down

  Refer to Fuel System Diagnosis.

• If the Active Fuel Injector Tester does not abort testing
4. Compare the test results with the appropriate recommended tolerance.
• If any fuel injector exceeds the recommended tolerance

  Replace the appropriate Q17 Fuel Injector(s).

• If all fuel injectors are within the recommended tolerance
5. Perform Fuel Injector Circuit Diagnosis.

1. Ignition ON.
2. Command the Fuel Pump Enable ON with a scan tool.
3. Verify the fuel pressure is between 345–690 kPa (50–100 PSI) with the fuel pump running.
• If not within 345–690 kPa (50–100 PSI)

  Refer to Fuel System Diagnosis.

• If within 345–690 kPa (50–100 PSI)

Note: 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.

4. Verify the fuel pressure does not decrease greater than 34 kPa (5 PSI) within 1 minute.
• If greater than the specified value

  Refer to Fuel System Diagnosis.

• If less than the specified value
5. Engine idling.
6. Verify the scan tool Fuel Rail Pressure Sensor 1 parameter is between 1.9–5.0 MPa (276–725 PSI).
• If not between 1.9–5.0 MPa (276–725 PSI)

  Refer to Fuel System Diagnosis.

• If between 1.9–5.0 MPa (276–725 PSI)

Note: The engine speed must be between 600–1,000 RPM to perform this test.

7. Select the Fuel Injector Balance function within the Control Functions menu of a scan tool.
8. Select and test a Q17 Fuel Injector. Repeat for each Q17 Fuel Injector.
9. Obtain and record a pressure drop value for each Q17 Fuel Injector.

Note: For engines with 2 cylinder banks, only measure the average pressure drop across cylinders that are on the same bank.

10. Add all of the individual pressure drop values except for the fuel injector suspected of being faulty. This is the total pressure drop.
11. Divide the total pressure drop by the number of fuel injectors that were added together. This is the average pressure drop.
12. Multiply the average pressure drop by 0.20. This is the acceptable variance from the average pressure drop, 20%.
13. Verify the difference between any individual pressure drop and the average pressure drop is not greater than the acceptable variance.
• If greater than the acceptable variance

  Replace the Q17 Fuel Injector.

• If within the acceptable variance
14. Perform Fuel Injector Circuit Diagnosis.

Perform the Diagnostic Repair Verification after completing the repair.

• Fuel Injection Fuel Rail Assembly Replacement - Bank 1
• Fuel Injection Fuel Rail Assembly Replacement - Bank 2