How if the machine intermittent low power

Intermittent Low Power or Power Cutout

Note: Use this procedure only if the engine does not shut down completely.

Probable Causes

* Diagnostic codes

* Event codes

* Turbocharger

* Air inlet and exhaust restrictions

* Throttle signal

* Power supply for the Electronic Control Module (ECM)

* Fuel supply

Recommended Actions

Note: If the problem only occurs under certain conditions, test the engine under those conditions. Examples of certain conditions are high engine speed, full load and engine operating temperature. Troubleshooting the symptoms under other conditions can give misleading results.

Diagnostic Codes and Event Codes

Certain diagnostic codes and/or event codes may cause poor performance. Connect the Caterpillar Electronic Technician (ET) and check for active codes and/or for logged codes. Troubleshoot any codes that are present before continuing with this procedure.

Turbocharger

Ensure that the turbocharger is operating correctly. Periodic inspection and cleaning is recommended for the turbocharger compressor housing (inlet side).

Air Inlet and Exhaust Restrictions

Check the air inlet system for the following problems: restrictions, collapse and pinched line. Repair the lines and/or replace the lines.

Check for an air filter restriction. Replace plugged air filters and/or clean filters. Repair any leaks.

Throttle Signal

Monitor the status for "Throttle Position" on Cat ET. Verify that the status for "Throttle Position" is stable and that the engine is able to reach high idle speed. Refer to the appropriate diagnostic test for your application:

* Troubleshooting, "Throttle Position Sensor Circuit - Test"

* Troubleshooting, "Throttle Switch Circuit - Test"

* Troubleshooting, "Speed Control - Test"

ECM Power Supply

1. Inspect the circuit between the ECM and the batteries. Refer to the Electrical System Schematic. Inspect the wires, the connectors, and the components in the circuit. Refer to the diagnostic functional test Troubleshooting, "Electrical Power Supply Circuit - Test" for more information.

2. Inspect the circuit between the ECM and the keyswitch. Refer to the Electrical System Schematic. Inspect the wires, the connectors, and the components in the circuit. Refer to the diagnostic functional test Troubleshooting, "Electrical Power Supply Circuit - Test" for more information.

Fuel Supply

1. Check the fuel lines for the following problems: restrictions, collapsed lines and pinched lines. If problems are found with the fuel lines, repair the lines and/or replace the lines.

2. Check the fuel tank for foreign objects which may block the fuel supply.

3. Prime the fuel system if any of the following procedures have been performed:

* Replacement of the fuel filters

* Service on the low pressure fuel supply circuit

* Replacement of unit injectors

Note: A sight glass in the low pressure supply line is helpful in diagnosing air in the fuel. For more information, refer to Systems Operation/Testing and Adjusting, "Air in Fuel - Test".

4. Cold weather adversely affects the characteristics of the fuel. Refer to the Operation and Maintenance Manual for information on improving the characteristics of the fuel during cold weather operation.

NOTICE

Do not crank the engine continuously for more than 30 seconds. Allow the starting motor to cool for two minutes before cranking the engine again.

5. Check the fuel pressure after the fuel filter while the engine is being cranked. Refer to Systems Operation/Testing and Adjusting, "Fuel System" for the correct pressure values. If the fuel pressure is low, replace the fuel filters. If the fuel pressure is still low, check the following items: fuel transfer pump, fuel transfer pump coupling and fuel pressure regulating valve. Refer to Systems Operation/Testing and Adjusting for more information.

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How to fix if the steering problem

Testing and Adjusting
784C and 785C Off-Highway Truck/Tractors Steering System


Steering System Troubleshooting

When a problem with the steering system is defined, use the following procedure:

1. Perform a visual inspection. Refer to Testing and Adjusting, "Visual Inspection".

2. If the problem has not been identified, do "Operation Checks".

3. If the problem is still undetermined, do "Performance Tests".

This procedure will help to identify the steering hydraulic system problems.
Operation Checks

The front wheels must be on a dry, smooth hard surface and the hydraulic oil in the steering system must be warm.

Start the machine. In first gear, slowly drive the machine while you turn the steering wheel. Drive the machine until the hydraulic oil temperature is approximately 65°C (150°F).

Test the steering system with the engine at high idle. Rotate the steering wheel. Measure the time that is required to turn the front wheels from the full right turn position to the full left turn position and back to the full right turn position. If the time is more than 9.0 seconds, there could be a problem in the steering hydraulic system. If the time is less than 7.0 seconds, there could be a problem in the steering hydraulic system.

Failures in the steering system can be at least one of the following items:

* Broken oil line or a leak in an oil line connection
* Worn hydraulic oil pump
* Pressure setting of the backup relief valve
* Worn steering metering pump
* Pressure setting of steering crossover relief valve
* Leaking steering crossover relief valve
* Worn steering cylinders
* Improperly charged accumulators
* Pressure setting of the pressure and flow compensator valve

Performance Checks

Performance checks of the steering system can be used for the following purposes:

* Diagnosis of poor performance
* Source of oil leakage inside the hydraulic system

Problem: Noisy steering pump
Probable Cause

* Air in the steering hydraulic circuit
* Loose connection of the oil line on the inlet side of the pump
* Low oil level in the steering hydraulic tank
* Wrong oil viscosity

Problem: Too much force is required to turn the steering wheel.
Probable Cause

* Open backup relief valve
* Low oil in the steering hydraulic tank
* Low oil pressure in the accumulator
* Worn pump
* Tight end cover on the steering metering pump
* Interference of components on steering column with shaft
* Improper operation of steering metering pump
* Improper operation of steering crossover relief valve
* Cold oil
* Restriction in the steering linkage
* The solenoid that is located on the steering solenoid and relief valve is bad.

Problem: The machine does not turn when the steering wheel is turned.
Probable Cause

* Air in system
* Malfunction in steering crossover relief valve
* Lack of oil in steering metering pump
* Worn steering metering pump
* Disengaged steering column shaft from steering metering pump

Problem: Erratic steering
Probable Cause

* Air in system
* Worn steering linkage
* Worn cylinder piston
* Loose cylinder piston
* Malfunction of steering crossover relief valve
* Incorrect timing of steering metering pump

For proper assembly of the steering metering pump, refer to System Operation, "Metering Pump (Steering)".

Problem: The machine turns too slowly in both directions.
Probable Cause

* Not enough oil flow from the steering pump
* Malfunction of steering crossover relief valve
* Failed accumulator

Problem: The machine turns too slowly in one direction.
Probable Cause

* Restriction in steering metering pump
* Malfunction of steering crossover relief valve

Problem: The steering wheel does not return to the center position correctly.
Probable Cause

* Tight cover on steering metering pump
* Interference of components on steering column with shaft
* Restriction between spool and sleeve in steering metering pump
* Damaged centering springs in steering metering pump
* Broken centering springs in steering metering pump

Problem: Hot oil temperature
Probable Cause

* The steering pump does not destroke.
* Wrong oil viscosity
* Air in the oil
* Low oil in the steering hydraulic tank
* Low pressure setting on the backup relief valve
* Restriction in the line circuit
* Oil leakage by the solenoid in the steering solenoid and relief valve.

Problem: Low oil pressure
Probable Cause

* Low pressure setting on the pressure and flow compensator valve
* Worn steering pump
* The solenoid that is located on the steering solenoid and relief valve is bad.

Problem: The steering wheel turns freely.
Probable Cause

* The sleeve and the spool in the steering metering pump stick due to foreign material.
* Broken centering springs in the steering metering pump
* Damaged centering springs in the steering metering pump
* Incorrect timing of steering metering pump

For proper assembly of the steering metering pump, refer to System Operation, "Metering Pump (Steering)".

Problem: The steering pump does not destroke.
Probable Cause

* High pressure setting of pressure and flow compensator valve
* Damaged steering pump

Problem: Soft steering
Probable Cause

* Air in the steering hydraulic circuit
* Low oil level in tank
* Nitrogen in the steering hydraulic system from a failed accumulator

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