992G Wheel Loader Electrohydraulic System Caterpillar

This procedure is used to determine if the pressure setting of the right backup relief valve for the variable displacement pump is lower than the cutoff pressure for the variable displacement pump.

The hydraulic fan must be at maximum speed when you perform the stall test. This will ensure that there is a consistent parasitic load on the engine. The Caterpillar Electronic Technician (ET) should be used in order to set the fan to maximum speed.

1. Move the machine to a level area.

2. Engage the parking brake.

3. Shift the transmission to the NEUTRAL position.

4. Start the engine. Warm the hydraulic oil to normal operating temperature of approximately 49 to 65°C (120 to 150°F).

5. Connect Caterpillar ET to the data link connector. The data link connector is next to the keypad. Start Caterpillar ET.

6. Select "3508B 992G". Select "Diagnostics and Diagnostic tests". Select "Override Parameters and Engine Fan Bypass".

7. Enter "0%" for the "Engine Fan Bypass Override Parameter". This should cause the fan to run at maximum speed when the engine is at high idle.

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Illustration 1	g00284487
Right Console (1) Keypad.

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Illustration 2	g00286975
Front Dash (2) Diagnostic message screen.

8. Press the "OK" key on keypad (1) repeatedly. The hourmeter will be displayed on the diagnostic message screen (2) .

9. Enter "SERV" on the keypad and then press the "OK" key. Press the ">" key until the diagnostic message screen displays the following message:
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   Table 1

   IMPL RLF - VAR PUMP

10. Press the "OK" key. The following message will be displayed on the diagnostic message screen:
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    Table 2

    IMPL RLF - VAR PUMP PRESS "OK" TO START

11. Press the "OK" key. The following messages will be displayed on the diagnostic message screen:
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    Table 3

    RLF PRES CHECK MODE IS TURNED ON

    RIGHT VALVE ONLY WILL BE COMMANDED

    PROCEED W/ STANDARD SERVICE CHECKS

    The following message will alternate with the previous message in five second intervals:

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    Table 4

    PRESS "<" OR ">" TO SEE SPEC LIST

    Note: The displayed specifications on the diagnostic message screen are the expected results for the test. The specifications in the service manual may not agree with the specifications on the diagnostic message screen. The service personnel should use the specifications that are displayed on the diagnostic message screen for testing. These specifications could be changed by future updates in the software for the implement ECM.

    Note: The following specifications are listed on the diagnostic message screen:

    • The setting for the high pressure cutoff on the variable displacement pump

    • The pressure setting for the dump line relief valves

    • The lift time for the bucket with the variable displacement pump

    • The torque converter stall speed

    • The double stall speed for the variable displacement pump

    • The setting for the variable displacement pump backup relief valve pressure

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Personal injury or death can result from machine movement. When tests and adjustments are made to the transmission or the torque converter, the parking brake must be disengaged. To prevent movement of the machine and personal injury perform the procedure that follows.

12. Release the parking brake.

13. Fully depress the service brake pedal. Hold the brake pedal in this position for the duration of this test.

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NOTICE
To make sure that the transmission oil does not overheat, do not keep the torque converter in a stall condition for more than 30 seconds. After the torque converter stall test, reduce engine speed to low idle, move the transmission control to neutral and increase the engine speed to approximately 1500 rpm to cool the oil.

14. Increase the engine speed to high idle.

15. Press the transmission shift control in order to select THIRD speed.

16. Move the transmission direction switch to the FORWARD position.

17. Allow the engine rpm to stabilize. Record the engine rpm. This is the torque converter stall speed.

18. Move the tilt lever to the TILT BACK position in order to tilt the bucket against the stops. Hold the lever in the TILT BACK position. The engine rpm will initially drop below the single stall speed. The engine rpm will then rise and the engine rpm will stabilize. Record the engine speed. This is the double stall speed of the variable displacement pump.

19. Move the tilt lever to the HOLD position. Reduce engine speed to low idle. Shift the transmission to the NEUTRAL position.

20. Allow the engine coolant and the transmission oil to cool.

21. Use Caterpillar ET in order to reset the "Engine Fan Bypass Override Parameter".

22. Exit the Caterpillar ET program and disconnect ET from the machine.

23. Stop the engine.

The double stall speed should equal the value listed in the SPEC LIST. If the pressure reading of the variable displacement pump was within specifications, this procedure is completed. The cutoff pressure of the variable displacement pump and the pressure of the backup relief valve are correct.

Note: Refer to the "SPEC LIST" in order to obtain the torque converter stall speed that is correct for your machine.

If the double stall speed is less than the stall speed listed on the SPEC LIST, the pressure setting of the right backup relief valve is less than the pressure cutoff of the variable displacement pump. The right backup relief valve may also be too close to the pressure cutoff of the variable displacement pump.

Reference: For the correct procedure to adjust the backup relief valve, refer to Testing and Adjusting, "Piston Pump Backup Relief Valve Pressure (Variable Displacement) - Test and Adjust" in this manual.