
RENR5622 47
Troubleshooting Section
i02385587
Engine Misfires, Runs Rough
or Is Unstable
SMCS Code: 1000-038; 1901-038
Note: If the sy
mptom is intermittent and the symptom
cannot be repeated, refer to Troubleshooting,
“Intermittent Low Power or Power Cutout”. If the
symptom is con
sistent and the symptom can be
repeated, continue with this procedure.
Probable Causes
•
Diagnostic c
odes
•
Electrical connectors
•
Cold mode
•
Throttle sig
nal
•
Unit injectors
•
Fuel supply
•
Air inlet and
exhaust system
Recommended
Actions
Note: If the symptom only occurs under certain
operating co
nditions (high idle, full load, engine
operating temperature, etc), test the engine under
those conditions. Troubleshooting the symptom
under other
conditions can give misleading results.
Diagnostic Codes
Check for active diagnostic codes on Caterpillar
Electronic Technician (ET). Troubleshoot any active
codes befor
e continuing with this procedure.
Electrical Connectors
Check for correct installation of the J1/P1 and J2/P2
Electronic Control Module (ECM) connectors and the
unit injec
tor connectors. Refer to Troubleshooting,
“Inspecting Electrical Connectors”.
Cold Mode
Use Cat ET to verify that the engine has exited cold
mode. Cold
mode operation may cause the engine to
run rough and the engine power may be limited.
Throttle S
ignal
Monitor the throttle signal on Cat ET. Verify that the
throttle
signal is smooth from the low idle position
tothehighidleposition.
Unit Injectors
1. Use Cat ET to determine if there are any active
diagnostic codes for the unit injectors.
2. Perform the “Injector Solenoid Test” on Cat ET in
order to determine if all of the injector solenoids
are being ener
gized by t he ECM.
3. Perform the “Cylinder Cutout Test” on Cat ET in
order to ident
ify any misfiring cylinder(s). Refer
to Troubleshooting, “Injector Solenoids” for more
information.
Fuel Sup ply
1. Check the fue
l lines for the following problems:
restrictions, collapsed lines, and pinched lines. If
problems are found with the fuel lines, repair the
lines and/or
replace the lines.
2. Check the fuel tank for foreign objects which may
block the fu
el supply.
3. Prime the fuel supply system if any of the following
procedures
have been performed:
•
Replacement of the fuel filters
•
Service on the low pressure f uel supply circuit
•
Replacemen
t of unit injectors
Note: A sight glass in the fuel supply line is helpful in
diagnosing
air in the fuel.
4. Cold weather adversely affects the characteristics
of the fuel
. Refer to the Operation and
Maintenance Manual for information on improving
the characteristics of the fuel during cold weather
operation
.
5. Check the fuel pressure during engine cranking.
Check the f
uel pressure after the fuel filter. Refer
to the Systems Operation/Testing and Adjusting
manual for the correct pressure values. If the fuel
pressure
is low, replace the fuel filters. If the fuel
pressure is still low, check the following items: fuel
transfer pump, fuel transfer pump coupling, and
fuel pres
sure regulating valve.
Air Inlet and Exhaust System
1. Check for an air filter restriction. Clean plugged air
filters or replace plugged air filters. Refer to the
Operati
on and Maintenance Manual.
2. If air shutoff valves are installed, verify that the air
shutoff
valves are fully opened.