Fuel Injector Balance Test - Fuel Pressure Test

FUEL INJECTOR DIAGNOSIS

DIAGNOSTIC FAULT INFORMATION

IMPORTANT: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Testing and Inspection

CIRCUIT/SYSTEM DESCRIPTION
The control module enables the appropriate fuel injector pulse for each cylinder. The ignition voltage is supplied directly to the fuel injectors. The control module controls each fuel injector by grounding the control circuit via a solid state device called a driver. A fuel injector coil winding resistance that is too high or too low will affect the engine driveability. A fuel injector control circuit DTC may not set, but a misfire may be apparent. The fuel injector coil windings are affected by temperature. The resistance of the fuel injector coil windings will increase as the temperature of the fuel injector increases.

When performing the fuel injector balance test, the scan tool is first used to energize the fuel pump relay. The fuel injector tester or 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 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 coil test within the conditions of the customers concern. A fuel injector condition may only be apparent at a certain temperature, or under certain conditions.

COMPONENT TESTING

Fuel Injector Balance Test-Fuel Pressure Test
1. Install a fuel pressure gage.
2. Turn ON the ignition, with the engine OFF.
3. Command the fuel pump relay ON with a scan tool.

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.

4. Observe the fuel pressure gage with the fuel pump commanded ON. The fuel pressure should be 345-414 kPa (50-60 psi).
- If the fuel pressure is not 345-414 kPa (50-60 psi), refer to Fuel System Diagnosis. Component Tests and General Diagnostics
5. Monitor the fuel pressure gage for one minute. The fuel pressure should not decrease more than 34 kPa (5 psi).
- If the fuel pressure decreases more than 34 kPa (5 psi), refer to Fuel System Diagnosis. Component Tests and General Diagnostics

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.

6. Perform the Fuel Injector Balance Test with Special Tool or the Fuel Injector Balance Test with Tech 2.

Pressure Drop Calculation
1. Subtract the second pressure reading from the first pressure reading for one fuel injector. The result is the pressure drop value.
2. Obtain a pressure drop value for each fuel injector.
3. Add all of the individual pressure drop values. This is the total pressure drop.
4. Divide the total pressure drop by the number of fuel injectors. This is the average pressure drop. The difference between any individual pressure drop and the average pressure drop should not be more than 20 kPa (3 psi).
- If the difference between any individual pressure drop and the average pressure drop is more than 20 kPa (3 psi), replace the fuel injector.

REPAIR INSTRUCTIONS

IMPORTANT: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

Fuel Injector Replacement