N14 Base Engine Troubleshooting and Repair Manual – Fuel Consumption Excessive (PT)

Symptom Tree  t087-011

This is symptom tree t087-011
Cause Correction

Interview the operator to verify the complaint

Refer to Fuel Consumption – General Information and Customer Complaint form at the end of Section TS. Follow the instructions on the forms before continuing with this tree.


Fuel economy expectations are not reasonable

Verify what factors compose the operator’s expectations. Run a VE/VMS® simulation for automotive applications to determine the expected fuel economy or perform a trial run to establish the actual fuel economy. Refer to the OEM service manual.


Fuel consumption is changing due to seasonal or operational changes

Review fuel consumption records for the past 3 to 6 months to determine the effects of seasonal or operational changes.


Drivetrain is not correctly matched to the engine

Check for correct gearing and drivetrain components. Make sure the propeller size is correct.


Fuel consumption and/or oil consumption data are inaccurate

Verify fuel consumption and/or oil consumption data. Refer to the OEM specifications.


Vehicle has changed routes or loads

Consider operating environment and its effect on fuel economy. Adverse weather, strong head winds, variable routes, and heavier loads can increase fuel consumption.


Fuel grade has changed

Number 1 diesel fuel and other light winter fuels are lower in heat content than number 2 diesel fuel and result in higher fuel consumption. Evaluate fuel consumption using number 2 diesel fuel. Fuel additives also result in lower heat content.


Coolant temperature is below specification

Refer to the Coolant Temperature Below Normal symptom tree.


Lubricating oil temperature is below specificationthe Coolant Temperature Below Normal symptom tree

Install an oil pan heater, or drain the oil and fill the system with warm oil.


Vehicle or trailer brakes are dragging

Check the brakes for dragging. Refer to the OEM service manual.


Wheel alignment is not correct (tractor or trailer)

Check the wheel alignment. Refer to the OEM service manual and the manufacturer’s instructions.


Tires on the tractor or trailer are new

New tires add up to 3 percent to rolling radius. Verify tire revolutions per mile with new tires and calculate fuel consumption. For electronic engines, enter the correct value for tire revolutions per mile in the ECM.


Hour meter is miscalibrated

Check the hour meter. Calibrate or replace the hour meter if necessary. Calculate fuel consumption with new figures.


Tires on the tractor or trailer are worn or have low-pressure

Check the tires on the tractor and trailer. Repair or inflate the tires as necessary. Evaluate fuel consumption again.


Fuel consumption has increased after an engine repair

Evaluate the engine repair to determine its effect on fuel consumption. Check part numbers to make sure the correct parts were used. Refer to the Control Parts List (CPL), Bulletin 3379133.


Operator technique is not correct

Explain correct engine operation to the operator. Refer to the OEM service manual.


Fuel leak

Check the fuel lines, fuel connections, and fuel filters for leaks using the combustible gas detector service tool. Refer to Procedure 006-024.


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 Procedures 007-009 and 007-037.


Air intake system restriction

Check the air intake system for restriction. Refer to Procedure 010-031.


Exhaust system restriction

Check the exhaust system for any restrictions. Refer to Procedure 011-009.


Intake manifold pressure (boost) is below specification

Refer to the Intake Manifold Pressure (Boost) is Below Normal symptom tree.


Air intake or exhaust leaks

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


Charge air cooler is restricted or leaking

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


Injector cup is damaged or is not correct

Check the injector cups for damage and for correct part numbers. Refer to Procedure 006-026.


Overhead adjustments are not correct

Measure and adjust the overhead settings. Refer to Procedure 003-004.


Fuel drain line is bent

Check the fuel drain line. Repair if necessary. Refer to Procedure 006-012.


Injector calibration is not correct

Calibrate the injectors. Refer to Procedure 006-026.


Static injection timing is not correct

Check the static injection timing. Refer to Procedure 006-025.


Step timing control system not switching to advanced timing mode

Inspect step timing control operation. Refer to Procedure 006-037.


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

Operate the engine from a tank of high-quality fuel. Refer to Fuel for Cummins Engines, Bulletin 3379001.

Last Modified:  29-Mar-2005