Cummins N14 STC, Celect, Celect Plus – Service Manual Engine Power Output Low (PT™)

Symptom Tree  t057-011

This is symptom tree
Cause Correction

Interview the operator to verify the complaint

Refer to Driveability – General Information, the Driveability/Low Power Customer Complaint Form, and the Driveability Checklist at the end of Section TS. Follow the instructions on the form before continuing with this tree.


Drivetrain is not correctly matched to the engine

Check for correct gearing and drivetrain components. Refer to the OEM vehicle specifications.


Lubricating oil level is above specification

Check the oil level. Verify the dipstick calibration and oil pan capacity. Fill the system to the specified level. Refer to Procedure 007-009 and Procedure 007-025 in Section 7.


Fuel grade is not correct for the application, or the fuel quality is poor

Operate the engine from a tank of known high quality fuel. Refer to Fuels for Cummins® Engines, Bulletin 3379001.


Air intake or exhaust leaks

Inspect the air intake and exhaust systems for air leaks. Refer to Procedure 010-024 in Section 10.


Fuel inlet temperature to pump is above specification

Fill the fuel tank, turn off or bypass the fuel heaters, and check the fuel cooler. Refer to the OEM service manual.


Air intake system restriction is above specification

Inspect the air intake system for restriction. Clean or replace the air filter and inlet piping as necessary. Refer to Procedure 010-031 in Section 10.


Intake manifold air temperature is above specification

Refer to the Intake Manifold Air Temperature Above Specification troubleshooting symptom tree in Section TS.


Charge-air cooler is restricted or leaking

Inspect the charge-air cooler for air restrictions or leaks. Refer to Procedure 010-027 in Section 10.


Intake manifold pressure (boost) is below specification

Refer to the Intake Manifold Pressure (Boost) is Below Normal troubleshooting symptom tree in Section TS.


Throttle linkage adjustment is not correct

Check the fuel pump throttle linkage adjustment. Refer to Procedure 005-036 in Section 5.


Tachometer or speedometer is not calibrated or is malfunctioning

Compare the vehicle tachometer and speedometer readings with an electronic service tool reading. Check the calibration values for the flywheel teeth, rear axle ratio, and tire revolutions. Adjust the values if necessary. Refer to the OEM service manual.


Engine is operating above recommended altitude (STC engines only)

Derate the engine by 4 percent for every 300 meters [1000 feet] of altitude above 3600 meters [12,000 ft]. Refer to the Engine Data Sheet.


Engine components are not correct

Compare the Control Parts List (CPL) to the engine components. Replace components that do not meet CPL requirements. Refer to Control Parts List, Bulletin 3379133.


Fuel supply pressure is below specification

Measure the fuel supply pressure.


Fuel supply line restriction between the fuel pump and the injectors

Check the fuel supply line from the fuel pump to the cylinder head for sharp bends that can cause restrictions. Refer to the OEM service manual.


Turbocharger wheel clearance is out of specification

Check the radial bearing and axial clearances. Inspect the turbocharger. Repair or replace the turbocharger, if necessary. Refer to Procedure 010-038 and Procedure 010-047 in Section 10.


Crankcase pressure is excessive

Check for excessive blowby.Refer to the Crankcase Gases (Blowby) Excessive troubleshooting symptom tree in Section TS.


Overhead adjustments are not correct

Check and adjust the overhead settings. Refer to Procedure 003-004 in Section 3.


Engine is operating at high ambient temperature

Use outside air to the turbocharger in hot weather.


Engine is operating at low ambient temperature

Check the winterfront, shutters, and under-the-hood air. Use under-the-hood intake air in cold weather. Refer to Operation of Diesel Engines in Cold Climates, Bulletin 3379009.


Fuel temperature is above specification

Fill the fuel tanks. Turn off or bypass the fuel heater, if equipped. Refer to the OEM service manual.


AFC signal line is restricted or leaking

Check the AFC signal line for restriction and leaks. Refer to Injector Specifications Manual, Bulletin 3379664.


Injector calibration is not correct or the fuel supply to the injector is restricted (PT injectors)

Remove the injectors. Check the injectors for the correct calibration. Check the inlet screen for restriction. Check for carbon buildup on the plungers. Refer to Procedure 006-026 in Section 6 and the Injector Specifications Manual, Bulletin 3379664.


Keyswitch circuit is malfunctioning

Check the vehicle, equipment, or vessel keyswitch circuit. Refer to the OEM service manual.

Last Modified:  20-Mar-2012