Part 4 of 4

Chart A-3 Part 4 Of 4:

Wiring Diagram:

CIRCUIT DESCRIPTION:

During cranking, the ignition module monitors the dual crank sensor sync signal. The sync signal is used to determine the correct cylinder pair to spark first. After the sync signal has been processed by the ignition module, it sends a fuel control reference pulse to the ECM. When the ECM receives this pulse, it will command all six injectors to open for one shot of fuel in all cylinders. After the priming, the injectors are left off for the next six fuel control reference pulses from the ignition module. This allows each cylinder a chance to use the fuel from the priming shot. During this waiting period, a cam pulse will have been received by the ECM. Now the ECM begins to operate the injectors sequentially, based on true camshaft position. However, if the cam signal is not present at start-up a Code 41 will set and the ECM will start sequential fuel delivery in any old random pattern. There is a 1 chance in 6 that fuel delivery will be correct. The sync signal is used only by the ignition module. It is used for spark synchronization at start-up only and not passed onto the ECM.

NOTE: Because of all the possible color code combinations used on electrical wiring diagrams, always refer to SCHEMATIC DIAGRAMS/ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS/ECM CONNECTOR IDENTIFICATION for correct color code identification of circuit.

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

10. Jumping the crank sensor harness terminals "B" and "C" together, a crank signal is simulated. This signal will then cause the ECM to energize the fuel pump relay for 2 seconds, and you can here it clicking "ON" and "OFF."

11. Verifies a proper crank signal circuit voltage of 9 to 12 volts and a good ground from the ignition module to terminal "C" of the sensor connector.

12. Determines the reason for incorrect voltage reading was due to a fault in CKT 643, an open in CKT 645, or a faulty ignition module.