Water Delivery System and 777F WTR, 777G WTR and 785D WTR OEM Off-Highway Trucks Caterpillar

Water System Pressure Is Low

Usage:

785D DMC

This message is recorded when the WDS ECM reads the signal from the WDS water pressure sensor as being lower than the desired water pressure.

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Illustration 1	g03610786

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Illustration 2	g03610787

Note: Hydraulic pressure regulation is controlled mechanically and electronically. This control ensures that the truck and equipment are not inadvertently damaged by high hydraulic pressure. High hydraulic pressure can overload the engine capacity or damage the Water Delivery System hydraulic seals.

Note: During operation, if the hydraulic pressure exceeds 24132 kPa (3500 psi) for 1 second the maximum amount of current available to control the water spray is reduced by 5 mA every second, until the system hydraulic pressure returns to a value under 24132 kPa (3500 psi). That new maximum value will be the maximum output available until the water pump is cycled off and back on.

Note: If the system is extensively operated with high hydraulic pressure, current sent to the valve that controls water pump speed and water pressure is reduced. In this case, system performance is decreased.

Note: If this performance degradation is observed, the system should be checked to make sure that the hydraulics and water systems are functioning properly. Extended operation at hydraulic pressure greater than 24132 kPa (3500 psi) is not normal. If everything checks fine a simple cycle of the water pump on button should restore 100 percent capability to the water spray pressure.

The possible causes of low water pressure are listed below:

Blocked water piping
Failed water pressure sensor
Incorrect hose connection
Failed water pump
Failed charge pump
Failed hydraulic pump
Failed hydraulic motor

Check Hydraulic Hose Connection
1. Park the machine. Turn key start switch to the OFF position.
2. Inspect the main hydraulic hose connection between the piston pump and motor.
3. Inspect the signal and pilot/servo hose connection between the pump and motor.
4. Turn the key start switch to the ON position. Start the engine, and let the engine idle.
5. Select the "cannon" mode on the WDS keypad.
6. Position the water cannon to spray into a remote location.
7. Turn on the WDS water pump.
8. Observe and compare the direction of rotation of the water pump shaft with the direction indicated on the water pump housing.
  Expected Results: The hoses are connected according to the schematics. The water pump direction of rotation is the same as indicated on the pump housing.
  Results:
  OK - Hydraulic hose connection and direction of pump rotation is OK. Proceed to Step 2.
  Not OK - The pump is turning in opposite direction.
  Repair: Reconnect the piston pump and motor hose according to hydraulic schematics.
  STOP.
  Not OK - The signal and pilot/servo hose connection is not correct.
  Repair: Reconnect the signal and pilot/servo hose connection according to hydraulic schematics.
  STOP.
Check Water Pump Speed
1. Add reflective tape to water pump shaft to measure shaft speed.
2. Turn the key start switch to the ON position. Start engine and let the engine idle.
3. Select the "cannon" mode on the WDS keypad.
4. Position the water cannon to a spray into a remote location.
5. Turn on the WDS water pump.
6. Ensure that the WDS oil temperature is above 65° C (149° F).
7. Ensure that there is no excess water leakage on water piping or water pump seal.
8. Use a 368-9910 Multi-Tool Group to observe the water pump shaft speed.
  Expected Result: The water pump speed at low idle with cannon water pressure at 414 kPa (60 psi) is approximately 1600 rpm.
  Result: The water pump shaft speed is greater than 1800 rpm. Proceed to Step 3 to troubleshoot for a possible block in the water pump suction lines or a failed sensor.
  Result: The water pump shaft speed is less than 1400 rpm. Proceed to Step 5 to troubleshoot for a possible failed water pump, hydraulic pump and hydraulic motor.
Check WDS Water Pump Suction and Discharge
1. Turn the key start switch to the OFF position.
2. Access the suction sump and discharge of the water pump.
  Expected Result: No debris is present in the pump suction and discharge.
  Results:
  OK - No debris is present in water pump suction and discharge. Proceed to Step 4.
  Not OK - Debris is present in water pump suction or discharge.
  Repair: Clean the water pump suction and discharge. Check for the error code. If the issue is resolved, stop. If the issue not resolved, proceed to Step 4.
Check Water Pressure Sensor
1. Park the machine. Turn the key switch to the OFF position.
2. Install a 376-4170 Pressure Sensor from the 368-9910 Multi-Tool Group in the water piping close to the WDS water pressure sensor.
3. Turn the key start switch to the ON position. Start engine and let the engine idle.
4. Select the "cannon" mode on the WDS keypad.
5. Position the water cannon to a spray into a remote location.
6. Turn on the WDS water pump.
7. Ensure that the WDS oil temperature is above 65° C (149° F).
8. Observe the water pressure from the diagnostic pressure gauge.
  Expected Result: The water pressure at low idle in cannon mode is 414 kPa (60 psi).
  Results:
  Not OK - The measured water pressure is greater than 517 kPa (75 psi). The water pressure sensor has failed.
  Repair: Replace the water pressure sensor.
  STOP.
  Not OK - The measured water pressure is the same as the WDS sensor pressure and is less than 345 kPa (50 psi). The low pressure is possibly caused by water leakage in the internal and/or external water tank piping.
  Repair: Repair or replace the water tank piping.
  STOP.
Check WDS Oil Filter
1. Park the machine. Turn the key switch to the OFF position.
2. Remove the WDS oil filter.
3. Cut open the filter and check for metal debris.
  Expected Result: The WDS oil filter is clean.
  Results:
  OK - No contaminant-related failure. Proceed to Step 6.
  Not OK - The filter has excess metal debris. The hydraulic pump or motor has failed.
  Repair: Replace the WDS hydraulic pump, hydraulic motor and charge pump. Flush the WDS hydraulic system.
  STOP.
Check Hydraulic Pressure
1. Park the machine. Turn the key switch to the OFF position.
2. Install a 376-4170 Pressure Sensor from the 368-9910 Multi-Tool Group in the suction port of the WDS pump. This port is labeled "Ms". Install a 376-4171 Pressure Sensor from the 368-9910 Multi-Tool Group in the discharge port of the WDS pump. This port is labeled "Mp".
3. Turn the key start switch to the ON position. Start engine and let the engine idle.
4. Select the "cannon" mode on the WDS keypad.
5. Position the water cannon to a spray into a remote location.
6. Turn on the WDS water pump.
7. Ensure that the WDS oil temperature is above 65° C (149° F).
8. Observe the hydraulic pressure on the pressure gauges
  Expected Result: The suction port pressure is approximately 1862 kPa (270 psi). The discharge port pressure is between 20684 kPa (3000 psi) and 22063 kPa (3200 psi).
  Results:
  Not OK - Suction pressure is less than 1655 kPa (240 psi) and discharge pressure is less than 17237 kPa (2500 psi). The possible cause could be a loss of charge pressure due to charge pump failure, WDS piston pump failure, or motor failure. Proceed to Step 7.
  Not OK - Suction pressure is in range, but discharge pressure is greater than 24132 kPa (3500 psi). The possible cause could be water pump bearing failure, motor failure, or incorrect hydraulic hose connection. Proceed to Step 9.
  Not OK - Suction pressure is in range but discharge pressure is less than 17237 kPa (2500 psi). The possible cause could be hydraulic pump or motor failure. Proceed to Step 8.
Check Charge Relief Valve
1. Park the machine. Turn the key switch to the OFF position.
2. Remove the charge relief valve from the WDS piston pump.
3. Inspect the charge relief valve.
  Expected Result: The charge relief valve is clean and functional.
  Results:
  OK - The charge relief valve is OK. Proceed to Step 8.
  Not OK - The charge relief valve is dirty or non-functional.
  Repair: Clean or replace the charge relief valve. Repeat Step 6.
  STOP.

Check WDS Pump and Motor Case Drain Flow

Park the machine. Turn the key switch to the OFF position.
Connect a flow meter to the case drain of the WDS piston pump and motor. The port size is M22x1.5. Use a 4C-9910 Portable Hydraulic Tester with a 4C-9911 Flow Meter Gp.
Turn the key start switch to the ON position. Start engine and let the engine idle.
Select the "cannon" mode on the WDS keypad.
Position the water cannon to a spray into a remote location.
Turn on the WDS water pump.
Ensure that the WDS oil temperature is above 65° C (149° F).

Observe the case drain flow.

Expected Result: The measured case drain flow at low idle matches the values given in Table 1.

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Table 1
Machine	Pump Case Drain Flow	Motor Case Drain Flow
777F	10.6 L/min (2.8 US gpm)	15.1 L/min (4.0 US gpm)
777G	11.4 L/min (3.0 US gpm)	15.1 L/min (4.0 US gpm)
785D	12.1 L/min (3.2 US gpm)	15.1 L/min (4.0 US gpm)

Results:

OK - The case drain flow is within range. Proceed to Step 10.

Not OK - If the total measured case drain flow is less than expected, then the charge pump has failed, or the charge cold relief valve has failed.

Repair: Check the charge cold relief valve by disconnecting the return hose from the valve to the WDS hydraulic tank, and check for oil flow. Replace cold relief valve if there is oil flow.

STOP.

Repair: If cold relief valve is OK, replace charge pump.

STOP.

Not OK - If measured case drain flow is higher than expected in the pump, then the WDS pump has failed.

Repair: Change the WDS pump.

STOP.

Not OK - If the measured case drain flow is higher than expected in the motor, then the WDS pump has failed.

Repair: Change the WDS pump.

STOP.

Check WDS Water Pump
1. Turn the key switch to the OFF position.
2. Remove the WDS piston motor from the water pump.
3. Rotate water pump shaft manually.
  Expected Result: The water pump shaft rotates freely.
  Results:
  OK - The shaft rotates freely. The WDS motor has failed.
  Repair: Inspect and replace the WDS piston motor.
  STOP.
  Not OK - The shaft does not rotate freely. The water pump has failed.
  Repair: Inspect and repair or change water pump.
  STOP.
Check WDS Water Pump Solenoid
1. Park the machine. Turn the key switch to the OFF position.
2. B. Measure WDS piston pump solenoid resistance.
  Expected Result: Coil resistance is approximately 26 ohms.
  Results:
  OK - Coil resistance is correct.
  Repair: Change the WDS pump.
  STOP.
  Not OK - Coil resistance is incorrect.
  Repair: Change the WDS pump solenoid.
  STOP.