Fuel Injector Coil Test

Circuit Description
The Injector Flow/Voltage Drop Check compares the fuel pressure drop when each injector is pulsed for a set amount of time. Since each injector pulses the same, the fuel pressure drop for each injector should be approximately the same. Any of the suspect fuel injectors can be identified by either a too high or a too low fuel pressure drop. This check also determines if the voltage drop of the injector is within specification. Injector voltage drop out of specification can cause driveability conditions that are intermittent or that do not show up during an injector flow check. This chart requires the J 34730-91 Fuel Pressure Gauge, the J 39200 Voltmeter and the J 39021 Fuel Injector Tester.

Test Description
The numbers below refer to the step numbers on the Diagnostic Table.

Caution: Wrap a shop towel around the fuel pressure connection in order to reduce the risk of fire 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.

3. The first second of the voltage displayed by the DMM may be inaccurate due to the initial current surge, therefore, record the lowest voltage displayed by the DMM after the first second of the test. The voltage that is displayed by the DMM should be within the specified range (refer to the example). The voltage that is displayed by the DMM may increase throughout the test as the fuel injector windings warm and the resistance of the fuel injector windings changes. An erratic voltage reading (large fluctuations in the voltage that do not stabilize) indicates that there is an intermittent connection within the fuel injector.