D
Group 20
Uneven Operation, Fault Tracing
Symptom fault tracing
Depending on the vehicle configuration, conditions related
to uneven running may be caused or influenced by specific
faults or malfunctions in other vehicle components. These
include components such as automatic transmissions,
bodybuilder adaptations, etc. In such cases, also refer to
the specific Service Information for those components.
Note: You must read and understand the precautions
and guidelines in Service Information, group 20,
"General Safety Practices, Engine" before performing any
suggested procedures. If you are not properly trained and
certified in a procedure, ask your supervisor for training
before you perform it.
“General Information” page 71
For specific symptoms, see:
•
“Engine Runs Unevenly at Idle Speed” page 73
•
“Engine Speed Surges at Low or High Idle” page 73
•
“Engine Runs Unevenly or Misfires” page 73
•
“Engine Speed Surges Under Load or in Normal
Operating Range” page 73
•
“Engine Speed Surges in Power Take-off or Cruise
Control” page 74
“Symptom, Fault Tracing” page 3
General Information
Note: During fault tracing, the engine should be run at
the operating temperature as well as at the temperature
where the symptom occurs. Do not activate the exhaust
pressure governor.
•
Uneven engine operation is usually caused by faults in
the fuel system, faults in the exhaust system, unstable
electrical conditions, or poor fuel quality.
•
The engine runs unevenly at idle speed or is irregular
at operating speeds.
C2002642
Uneven Operation (Misfiring)
Misfires which do not produce fault codes are often very
difficult to find.
The basic cause of the misfiring could include one or
more of the following:
•
Mechanical fault in the engine.
•
Unstable electrical conditions.
•
Incorrect sensor signals.
•
No fuel injection or lack of fuel.
•
Ignition temperature too low in one of the cylinders.
•
The ignition point of the fuel is too low.
•
A sensor signal switches between defective and fault
free.
•
EGR valve(s) stuck open (rough idle)
71
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