B5.9G, B5.9LPG – Troubleshooting and Repair Manual – Fuel Consumption Excessive

Interview the operator to verify the complaint

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

Verify the complaint

Test the engine operation while under load. Perform an engine acceleration test. Perform an engine load/install test. Refer to Procedure 014-002. If engine has low or high power, refer to the Engine Power Output is Low or Engine Power Output is High symptom tree.

Fuel consumption and/or oil consumption data are inaccurate

Verify fuel consumption and/or oil consumption data. Refer to the Operation and Maintenance Manual, B5.9G, B5.9LPG, B Gas Plus, and B LPG Plus Engines, Bulletin 3666112.

Vehicle is not being fueled completely

Verify all fuel tank supply valves are open and the tanks contain fuel.

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.

Operator technique is not correct

Explain correct engine operation to the operator. Refer to the Operation and Maintenance Manual, B5.9G, B5.9LPG, B Gas Plus, and B LPG Plus Engines, Bulletin 3666112.

Electronic fault codes active or high counts of inactive fault codes

Refer to Section TF in the Troubleshooting and Repair Manual, Fuel Systems and Electronics, B5.9G, C8.3G, L10G-III, Bulletin 3666118, for fault code troubleshooting.

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 vehicle specifications.

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.

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 Fuels for Cummins Engines, Bulletin 3379001.

Oxygen sensor offset parameter is not correct

Verify that the offset parameter on the oxygen sensor tag matches the oxygen sensor offset parameter listed in INSITE™. Refer to the INSITE™ User’s Manual, Bulletin 3885798.

Fuel leak

Check the fuel lines, fuel connections, and fuel filters for leaks using the combustible gas detector service tool. Refer to Procedures 005-003, 005-047, and 005-052.

Drivetrain is not correctly matched to the engine

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

Coolant temperature is below specification

Refer to the Coolant Temperature is Below Normal symptom tree.

Lubricating oil temperature is below specification the Coolant Temperature is Below Normal symptom tree

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

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 007-025.

Wheel alignment is not correct (tractor or trailer)

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

Hubometer or odometer is miscalibrated

Check the hubometer and odometer calibrations. Calibrate or replace the hubometer or odometer, if necessary. Calculate fuel consumption with new mileage figures.

Speedometer is malfunctioning or the road speed is excessive

Calibrate the speedometer. Refer to the OEM service manual.

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.

Coil wire malfunctioning

Remove wire from engine and use a digital multimeter to measure resistance across the wire. Refer to Procedure 013-012.

Ignition coil malfunctioning

Check the ignition coil. Refer to Procedure 013-012.

Spark plug(s) damaged or incorrect gap

Inspect plug(s). Refer to Procedure 013-016.

Ignition system harness connector pins bent or damaged

Inspect harness. Refer to Procedure 019-196 in the Troubleshooting and Repair Manual, Fuel Systems and Electronics, B5.9G, C8.3G, L10G-III, Bulletin 3666118.

Battery voltage is low or bad ground connection at battery

Check the batteries. Check the battery circuit. The battery cable ground must measure within OEM specifications for voltage drop under electrical load. Refer to Procedure 013-007.

Air filter is restricted

Check the air filter for restrictions. Refer to the Operation and Maintenance Manual, B5.9G, B5.9LPG, B Gas Plus, and B LPG Plus Engines, Bulletin 3666112, and the OEM service manual.

Turbocharger wastegate is damaged or is stuck open

Check the wastegate for freedom of movement. Inspect the wastegate for damage. Refer to Procedure 010-050.

Exhaust system restriction is not within specification

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

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.

Overhead adjustments are not correct

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