Fuel Injector Balance Test

Circuit Description
The Fuel Injector Balance Test compares the performance of each of the cylinder by using the PCM to shut off fuel injection. The J 39021 Fuel Injector Tester is being used to energize the fuel injector for a precise time period. This measures the performance of each cylinder by the amount of RPM drop caused by that cylinder not producing a power stroke. If proper fuel delivery has been determined, then a cylinder that does not show good performance (RPM drop) indicates either an ignition or mechanical problem.

Diagnostic Aids
Any fuel injector that significantly (more than 10 kPa) requires service.

Test Description

Caution: Wrap a shop towel around the fuel pressure connection in order to reduce the risk of tire and personal injury. The towel will absorb any fuel leakage that occurs during the connection of the fuel pressure gauge. Place the towel in an approved container when the connection of the fuel pressure gauge is complete.

4. The engine coolant temperature must be below the operating temperature in order to avoid irregular fuel pressure readings due to Hot Soak fuel boiling.
5. The fuel pressure should be within the specified range. If the fuel pressure is not within the specified range, perform the Fuel System Diagnosis. Component Tests and General Diagnostics
6. The fuel pressure should reach a steady value. If the fuel pressure does not reach a steady value, perform the Fuel System Diagnosis.
7. 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.