C4.4 and C6.6 Engines for Caterpillar Built Machines Can Not Reach Top Engine RPM Caterpillar

Note: If this fault occurs only under load, refer to Troubleshooting, "Low Power/Poor or No Response to Throttle".

Probable Causes

• Diagnostic codes

• ECM parameters

• Air intake and exhaust system

• Fuel supply

• Individual malfunctioning cylinders

• Electronic unit injectors

Recommended Actions

Diagnostic Codes

Check for active diagnostic codes on the electronic service tool. Troubleshoot any active codes before continuing with this procedure.

ECM Parameters

1. Ensure that the problem is not a programmed parameter.

2. Ensure that the correct mode was selected by using the electronic service tool.

3. Use the electronic service tool to verify the correct engine rating for the engine.

4. Use the electronic service tool to verify the maximum engine speed limit.

5. Use the electronic service tool to verify the following parameters at maximum speed: the boost pressure, the smoke limit, the torque limit and the amount of fuel that is delivered.

6. Use the electronic service tool to reset the parameters to the OEM specifications.

7. Ensure that the repairs have eliminated the performance problems.

8. If the repairs have not eliminated the faults proceed to "Air Intake and Exhaust System".

Air Intake and Exhaust System

1. Check the air filter restriction indicator, if equipped.

2. Ensure that the air filter is clean and serviceable.

3. Check the air intake and the exhaust system for the following defects:

   • Blockages

   • Restrictions

   • Damage to the air intake and exhaust lines and hoses

4. Make all necessary repairs to the engine.

5. Ensure that the repairs have eliminated the fault.

6. If the fault has not been eliminated, proceed to "Fuel Supply".

Fuel Supply

1. Visually check the fuel tank for fuel. The fuel gauge may be faulty.

2. Ensure that the fuel supply valve is in the full OPEN position.

3. If the temperature is below 0 °C (32 °F), check for solidified fuel (wax).

4. Visually inspect the fuel supply lines for restrictions.

5. Check that the low pressure fuel lines are tight and secured properly.

6. Remove the fuel filters. Inspect the fuel filters for contamination. Install new fuel filters. Refer to the Operation and Maintenance Manual, "Fuel System Filter- Replace and Fuel System Primary Filter (Water Separator) Element - Replace". Determine the cause of the contamination.

7. Check the diesel fuel for contamination. Refer to Systems Operation, Testing and Adjusting, "Fuel Quality - Test".

8. Check for air in the low pressure fuel system. Refer to Systems Operation, Testing and Adjusting, "Air in Fuel - Test".

9. Ensure that the fuel system has been primed. Refer to Testing and Adjusting, "Fuel System - Prime".

10. Check the fuel pressure. Refer to Testing and Adjusting, "Fuel System Pressure - Test".
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    Contact with high pressure fuel may cause fluid penetration and burn hazards. High pressure fuel spray may cause a fire hazard. Failure to follow these inspection, maintenance and service instructions may cause personal injury or death.

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    NOTICE
    Contact with high pressure fuel may cause personal injury or death. Wait 60 seconds after the engine has stopped to allow fuel pressure to purge before any service or repair is performed on the engine fuel lines.

11. If the high pressure fuel lines have a leak, the high pressure fuel lines must be replaced. Refer to Disassembly and Assembly, "Fuel injection lines - Remove and Fuel injection lines - Install".

12. If the repairs do not eliminate the fault proceed to "Individual Malfunctioning Cylinders".

Individual Malfunctioning Cylinders

1. With the engine speed at a fast idle, use the electronic service tool to isolate one cylinder at a time. Note if there is any reduction in engine speed. If a reduction in engine speed is not noted, the isolated cylinder is not operating under normal conditions. If the isolation of a particular cylinder results in a reduction of engine speed that is less than normal, this may indicate that the cylinder is operating below normal performance. Investigate the cause of the fault on any cylinder that is not operating. Investigate the cause of the fault on any cylinder that is operating below normal performance.

2. If all cylinders have been checked and no faults were detected proceed to "Electronic Unit Injectors".

Electronic Unit Injectors

1. With the engine speed at a fast idle, use the electronic service tool to isolate one cylinder at a time. Note if there is any reduction in engine speed. If a reduction in engine speed is not noted, the isolated electronic unit injector is not operating under normal conditions. If the isolation of a particular cylinder results in a reduction of engine speed that is less than normal, this may indicate that the electronic unit injector is operating below normal performance.

2. Remove the electronic unit injector from the suspect cylinder. Refer to Disassembly and Assembly, "Electronic Unit Injector - Remove".

3. Install a new electronic unit injector. Refer to Disassembly and Assembly, "Electronic Unit Injector - Install".

4. Repeat the test in 1. If the fault is still apparent, remove the replacement electronic unit injector and install the original electronic unit injector. Refer to Disassembly and Assembly, "Electronic Unit Injector - Remove" and Disassembly and Assembly, "Electronic Unit Injector - Install".