Fuel Injector Electrical Circuit Diagnosis

NOTE: The fuel system wiring diagrams should be used in conjunction with the following test to correctly diagnose the problem.

1. Turn the ignition switch to the CRANK position.
2. Using a logic probe or a noid light, probe the injector electrical connectors and check that the injectors are receiving signals from the SBEC.
3. If there is no signal at any of the injector electrical connectors, disconnect the 60-Way SBEC electrical connector and the injector electrical connector, and perform the following steps:
a. Connect an ohmmeter across the LB/BK wire of injector #4 connector and pin No. 13 of the SBEC connector, and check for continuity. If there is no continuity, fix open in wire. If there is continuity, go to step 4.
b. Connect an ohmmeter across the YL/WT wire of injector #3 connector and pin No. 14 of the SBEC connector, and check for continuity. If there is no continuity, fix open in wire. If there is continuity, go to step 4.
c. Connect an ohmmeter across the TN wire of injector #2 connector and pin No. 15 of the SBEC connector, and check for continuity. If there is no continuity, fix open in wire. If there is continuity, go to step 4.
d. Connect an ohmmeter across the WT/DB wire of the injector #1 connector and pin No. 16 of the SBEC connector, and check for continuity. If there is no continuity, fix open in wire. If there is continuity, go to step 4.

4. Connect a voltmeter to the DG/BK wire (circuit A61) of each injector connector, and turn the ignition switch to RUN position. Voltage should be at the DG/BK wire of all injector electrical connectors. Check for voltage at each injector connector.
a. If there is less than 12 volts at any of the four injector connectors, connect a voltmeter to the DG/BK wire (terminal No. 87) of the Auto Shutdown (ASD) relay and check that there is 12 volts. If there is 12 volts at terminal No. 87, repair the wire(s) between the ASD relay and the injector connectors. If there is less than 12 volts at terminal No. 87 of the ASD relay, test the ASD relay.
b. If there is 12 volts at the injector connectors, and there is continuity between the injectors and their respective ground circuits to the SBEC (Pin No. 13, 14, 15, 16), the problem is computer related.