ISBe/ISB Series Engines – Engine Runs Rough or Misfires

Engine is cold

Allow the engine to warm to operating temperature. If the engine will notreach operating temperature, refer to the Coolant Temperature is Below Normalsymptom tree.

Electronic fault codes are active

For instructions on how to read active fault codes, refer to Diagnostic Fault Codes in Section 1. If fault codes are active, contact a Cummins Authorized Repair Facility.

Air in the fuel system

Check for air in the fuel system. Tighten or replace the fuel connections, fuel lines, fuel tank standpipe, and fuel filters as necessary.

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.

Moisture in the wiring harness connectors

Dry the connectors with Cummins electronic cleaner, Part Number 3824510.

Fuel quality is poor

Operate the engine from a temporary tank of good-quality number 2 diesel fuel. Clean and flush vehicle’s fuel system. Fill fuel system with a good-quality number 2 diesel fuel.

Vehicle parasitics are excessive

Check the vehicle brakes for dragging, transmission malfunction, cooling fan operation cycle time, and engine-driven units. Refer to the OEM service manual.