Operation and maintenance manual

Troubleshooting Symptoms Charts QSB4.5 and QSB6.7
Page TS-30 Section TS - Troubleshooting Symptoms
Engine Runs Rough or Misfires
Cause Correction
STEP 1
Engine is cold
.............
Allow the engine to warm to operating
temperature. If the engine will not reach operating
temperature, refer to the Coolant Temperature
Below Normal symptom tree.
OK
Go To Next Step
STEP 2
Electronic fault codes are active
.............
For instructions on how to read active fault codes,
refer to Section 1. If fault codes are active, contact
a Cummins Authorized Repair Facility.
OK
Go To Next Step
STEP 3
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. Vent air from the
system. Refer to Section 5.
OK
Go To Next Step
STEP 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 Fuel Recommendations and
Specifications in Section V.
OK
Go To Next Step
STEP 5
Fuel leak
.............
Check the fuel lines, fuel connections, and fuel
filters for leaks. Refer to the OEM service manual.
OK
Go To Next Step
STEP 6
Fuel filter is plugged
.............
Measure the fuel pressure before and after the fuel
filter. Refer to Section 5.
OK
Go To Next Step
STEP 7
Fuel supply is not adequate
.............
Check the flow through the filter to locate the
source of the restriction. Refer to Section 5.
OK
Go To Next Step
STEP 8
Fuel lift pump is malfunctioning
.............
Check the fuel lift pump for correct operation.
Check the pump output pressure. Replace the fuel
lift pump if necessary. Refer to an Authorized
Cummins Repair Facility.
OK
Go To Next Step
STEP 9
Engine mounts are worn, damaged, or not correct
.............
Check the engine mounts. Refer to the OEM
service manual.
OK
Go To Next Step