B5.9G, B5.9LPG – Troubleshooting and Repair Manual – Engine Speed Surges at Low or High 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 Engines, 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.

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.

Accessory load is excessive for the idle speed setting

Reduce the accessory load or increase the engine idle speed. Refer to Procedure 005-052 and the INSITE™ User’s Manual, Bulletin 3885798.

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.

Throttle plate is not closing completely

Check for a blocked accelerator pedal or linkage. Use INSITE™ to verify that the throttle plate is closing to 0 percent with no accelerator pedal. Refer to the INSITE™ User’s Manual, Bulletin 3885798.

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 Procedure 005-052 and the INSITE™ User’s Manual, Bulletin 3885798.

Intake manifold pressure sensor is malfunctioning

Check the intake manifold pressure sensor. Refer to Procedure 019-061 in the Troubleshooting and Repair Manual, Fuel Systems and Electronics, B5.9G, C8.3G, L10G-III, Bulletin 3666118.

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.

Fuel control valve is malfunctioning

Check the fuel control valve for sticking or hysteresis. Refer to Procedure 019-102 in the Troubleshooting and Repair Manual, Fuel Systems and Electronics, B5.9G, C8.3G, L10G-III, Bulletin 3666118.

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.

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.

Air intake manifold is leaking air

With the engine at idle, check for a vacuum (suction) around the intake manifold. Repair or replace the damaged components. Refer to Procedure 010-023.

Intake air restricted

Inspect and change air cleaner. Look for other restrictions. Refer to Procedure 010-031.

Turbocharger is malfunctioning

Monitor the turbocharger boost pressure with an electronic service tool. Refer to the appropriate electronic service tool manual. Replace the turbocharger if necessary. Refer to Procedure 010-033.

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.

Alternator is malfunctioning

Temporarily disconnect the alternator and run the engine. Replace the alternator if necessary. Refer to Procedure 013-001 and the OEM service manual.

Overhead adjustments are not correct

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

Exhaust system restriction is not within specification

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