Fuel Injector Balance Test

Fuel Injector Balance Test

Diagnostic Instructions

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

Circuit/System Description

When performing the fuel injector balance test, the scan tool will first crank the engine in order to pressurize the fuel rail. The scan tool is then used to pulse each injector 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 injector.

Diagnostic Aids

* 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.

Component Testing

Note:
* DO NOT perform this test if the engine coolant temperature (ECT) is above 60°C (140°F). Irregular fuel pressure readings may result due to hot soak fuel boiling.
* Verify that adequate fuel is in the fuel tank and that the battery is fully charged before proceeding with this diagnostic. It may be necessary to install a battery charger.

Fuel Injector Balance Test
1. Verify the correct low side fuel pressure. Refer to Fuel System Diagnosis (Fuel System Diagnosis).
2. With a scan tool, select the Fuel Injector Balance Test function within the Special Functions menu.

Warning

The engine will crank when performing the fuel injector balance test with a scan tool. Keep hands and tools away from the engine pulleys and belts during this test.

3. Select an injector to be tested.

Note: It may take up to two minutes before the injector will pulse after the engine stops cranking.

4. Press Enter to crank the engine, pressurize the fuel rail, and pulse the injector. The fuel rail will be pressurized before the injector is pulsed.
5. Repeat steps 3 and 4 for each fuel injector.
6. After all the injectors have been tested, view the results.
7. Add all of the individual pressure drop values except for the injector suspected of being faulty. This is the total pressure drop.
8. Divide the total pressure drop by the number of fuel injectors that were added together. This is the average pressure drop.
9. Multiply the average pressure drop by 0.20. This is the acceptable variance from the average pressure drop, 20 percent.

• If the difference between any individual pressure drop and the average pressure drop is more than the acceptable variance, replace the fuel injector.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

Fuel Injector Replacement (LLT) (Fuel Injector Replacement)