B5.9G, B5.9LPG, B Gas Plus, B LPG Plus – Engine Will Not Reach Rated Speed (RPM)

Symptom Tree  

Fuel level is low in the tank

Fill the supply tank. Refer to the OEM service manual.


Electronic fault codes active or high counts of inactive fault codes

Read the fault codes with an electronic service tool. Refer to Procedure 101-007 (Electronic Engine Controls) in Section 1 and a Cummins Authorized Repair Facility.


Engine is operating above recommended altitude

Engine power decreases above recommended altitude. Refer to the engine data sheet for specifications.


Ignition coil malfunctioning

Check the ignition coil. Refer to Procedure 013-012 (Ignition Coil) in Section 6 .


Spark plug(s) damaged or incorrect gap

Inspect plug(s). Refer to Procedure 013-016 (Spark Plug (Standard)) in Section 6 .


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 the OEM specifications.


Air intake leaks

Inspect and repair the intake air piping as needed. Refer to Procedure 010-058 (Air Intake Piping) in Sections 3.


Charge air cooler is restricted or leaking

Inspect the charge air cooler for air restrictions or leaks. Refer to Procedure 010-027 (Charge-Air Cooler) in Section A.


Air intake system restriction is above specification

Check the air intake system for restriction. Clean or replace the air filter and inlet piping as necessary. Refer to Procedure 010-059 (Air Cleaner Restriction) in Section 4.


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 Procedure 018-002 (Fuel Recommendations and Specifications) in Section V.


Intake manifold pressure sensor is malfunctioning

Check the intake manifold pressure sensor. Refer to a Cummins Authorized Repair Facility.


Drivetrain is not correctly matched to the engine

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


Automatic transmission shift points are not set correctly

Verify that shift points are set at approximately 200 rpm below rated speed. Contact the transmission manufacturer.


Tachometer is not calibrated or is malfunctioning

Compare the tachometer reading with a handheld tachometer or an electronic service tool reading. Calibrate or replace the tachometer as necessary. Refer to the OEM service manual.


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 a Cummins Authorized Repair Facility.


Electronic control module system is not calibrated or has incorrect calibration

Compare the calibration in the electronic control system with the engine rating and the Control Parts List (CPL), Bulletin 3379133 or 4021327. If necessary, calibrate the system. Refer to a Cummins Authorized Repair Facility.


Fuel leak

Check the fuel lines, fuel connections, and fuel filters for leaks using the combustible gas detector service tool. Refer to a Cummins Authorized Repair Facility.

Contact a Cummins Authorized Repair Facility

Last Modified:  15-Feb-2005