Diesel MFI Pump: Testing and Inspection

Figure 3-18: Stepper Motor Replacement:

Figure 3-19: Injection Timing Stepper Motor Circuit:

A stepper motor fault will affect desired and measured injection timing degree readings on the scan tool. A difference of 5° or more between the readings indicates a motor fault.

Stepper Motor Test

1. Connect the scan tool to the diagnostic/data link connector.
2. Start and run the engine until it reaches the normal operating temperature.
3. Note injection timing readings on the scan tool.
- If "desired" and "actual" injection timing readings differ by 5° or more, continue the test.
- If readings are no more than 3°-4° apart, but a trouble code was set, the problem is intermitent and probably caused by a bad connection between the PCM and the motor.

4. Stop the engine and turn ignition to Off.
5. Check the resistance between terminals A7 and A8 of the brown 24 pin PCM harness connector (C29) for coil 1 low (A8), and coil 1 high (A7) (Figure 3-19).
- If the resistance is between 10 and 50 ohms, continue test.
- If the resistance is not within the specified range, the problem is an open wire, a bad connection, or a failed stepper motor.

6. Check the resistance between terminals A9 and A10 of the brown 24 pin PCM harness connector (C29) coil 2 low (A9), and coil 2 high (A10) (Figure 3-19).
- If the resistance is 10-50 ohms, the problem is in the PCM connection, or the PCM.
- If the resistance is other than specified, the problem is in the wires to the PCM coil 2 terminals, a bad connection, or the PCM has a fault.