B5.9G, B5.9LPG – Troubleshooting and Repair Manual – Engine Runs Rough at Idle

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.

Engine is cold

Allow the engine to warm up for approximately 1 to 3 minutes. Refer to the Operation and Maintenance Manual, B5.9G, B5.9LPG, B Gas Plus, and B LPG Plus Engine, Bulletin 3666112.

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.

Low or no fuel pressure at the mixer (secondary pressure)

Use an electronic service tool to measure the fuel pressure after the gas mass flow sensor and before the mixer. Refer to Procedure 005-047.

Low or no fuel pressure at the fuel filter (primary pressure)

Use an electronic service tool to measure the fuel pressure at the fuel filter. Refer to Procedure 005-061.

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.

Engine idle speed is set too low

Use INSITE™ to verify that the engine idles at 600 rpm with no accessory load and 0-percent throttle when the idle bypass valve is unplugged. Adjust the idle setscrew if necessary. Refer to the INSITE™ User’s Manual, Bulletin 3885798, and Procedure 005-052.

Idle speed control valve malfunctioning

Inspect the idle speed control valve. Refer to Procedure 005-052.

Throttle position sensor or circuit malfunctioning (if equipped with a throttle position sensor)

Check the throttle position sensor and circuit. Refer to the Troubleshooting and Repair Manual, Fuel Systems and Electronics, B5.9G, C8.3G, L10G-III, Bulletin 3666118.

Accessory load is excessive

Check the accessory load and reduce the load if necessary. Refer to the OEM service manual.

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.

Heated oxygen sensor is damaged or has drifted

Use INSITE™ to check for significantly improved engine performance with the system in open-loop operation. Refer to the INSITE™ User’s Manual, Bulletin 3885798.

Oil from the fuel has accumulated on the gas mass flow sensor, screen packs, or elsewhere in the fuel system

Check for oil in the fuel system. Refer to Procedure 005-009.

Overhead adjustments are not correct

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

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.

Crankcase pressure is excessive

Check for excessive blowby. Refer to Procedure 003-021. Refer to the Crankcase Gases (Blowby) Excessive symptom tree.

Cylinder head valve leak

Check the cylinder head for fuel leaks between the valves and valve seats. Refer to Procedure 002-004.

Internal engine damage

Analyze the oil and inspect the filters to locate an area of probable damage. Refer to Procedure 007-083.