Fuel Injector Electrical Checks Using P.A.C.

After the mechanical condition of the injectors has been confirmed, it will be necessary to test the electrical operation of the injector circuit.





The best way to check the fuel injector electrical system is through the use of wave form patterns. Knowing how to interpret injector wave forms (determining on-time, referencing peak voltages, recognizing bad drivers, etc.) can provide further useful diagnostic information for the technician (Figure 4).

NOTE:
The Bear Uniscope's voltage scale is not adequate for injector testing.

Use the Snap-on(R) P.A.C.

Electrical Tests

The component in the ECM that controls the electrical operation of the injectors is called an injector driver. An injector driver is the solid state switch that the ECM uses to turn the injector on and off by providing a ground path.








1. Using the chart determine the multi-plug cavities for the injector driver contacts (Figures 2 and 3).

2. Set up the P.A.C. and back-probe the driver cavities for signals. Set scope at 100 volts and 5 ms.

3. Start engine and observe the wave form of the cylinder(s) flagged as having the misfire The coil release spike(s) should average 80 volts.





4. Compare the coil release spike(s) to Figure 4. An injector with a short in the coil will show a lower coil release spike.

5. If all the coil release spike heights are correct then you do not have a problem with the injector coil.

6. Set the P.A.C to the 50 volt scale.

7. Now observe the on time voltage reading. This reading should be under 1 volt.

8. If the reading on the various injector patterns is not even at 1 volt or less then you have a problem with the injector driver not pulling the circuit to ground.

9. Before replacing the injectors or the ECM perform continuity checks on the wiring harnesses and connectors between the injectors and the ECM. Pay particular attention to the ECM grounds.

NOTE:
If at the end of your tests you find that the fuel pressure drop tests and the wave form analysis are within specification, then you do not have a problem with the fuel injector system and you should look elsewhere for the cause of the problem.