Engine Misfires, Runs Rough or Is Unstable

TM 9-2320-312-24-2

Troubleshooting Section

Air Inlet Leaks

Note: If the problem only occurs under certain

conditions, test the engine under those conditions.

Inspect the air filter for leaks. Inspect all gaskets

Examples of certain conditions are high rpm,

and connections. Make repairs if leaks are found.

full load and engine operating temperature.

Troubleshooting the symptoms under other

conditions can give misleading results.

Fuel Leakage into the Engine Oil

Individual Cylinder Malfunction

Fuel leakage into the engine oil will cause high

fuel consumption and low engine oil pressure. This

condition may also increase the oil level in the

1. Check for an individual cylinder malfunction.

crankcase. Make repairs if leaks are found. Install

new parts, as required.

2. Ensure that the hydraulic electronic unit injector

connector (J300/P300) is fully connected and

Incorrect Engine Oil

ensure that the hydraulic electronic unit injector

connector (J300/P300) is free of corrosion.

Check oil recommendations for the proper oil

3. Ensure that the ECM engine harness connector

specifications for the engine operating conditions.

(J2/P2) is fully connected and ensure that the

engine harness connector (J2/P2) is free of

Incorrect Maintenance Interval

corrosion.

Review the oil change intervals in relation to the

4. Connect Caterpillar Electronic Technician (ET) to

nature and severity of the engine application.

the cab data link connector. Use the Cylinder

Review the records for the engine in order to verify

Cutout Test. Access the Cylinder Cutout Test

that the recommended intervals are being followed.

by selecting the "Diagnostic Menu" and the

"Diagnostics Test Menu". Run the Cylinder Cutout

Test in order to disable each cylinder. Disabling

i01641917

each cylinder allows the technician to isolate the

Engine Misfires, Runs Rough

misfiring cylinders.

or Is Unstable

If the misfiring cylinder can be isolated to

a specific cylinder, refer to Troubleshooting,

SMCS Code: 1000; 7569

"Injector Solenoid Circuit - Test".

Probable Causes

Fuel Supply

The probable root causes are listed in order below:

1. Monitor the exhaust for smoke while the engine

is being cranked.

Note: If the problem is intermittent and the problem

can not be duplicated, refer to Troubleshooting,

If no smoke is present, there may be a problem

"Intermittent Low Power or Power Cutout".

with the fuel quality or there may be a problem

with the fuel supply.

Individual cylinder malfunction

2. Check the fuel quality. Refer to the Truck

Fuel supply

Performance and Driveability Diagnostic Guide,

LEBT3477.

Low injection actuation pressure

3. Check the fuel pressure. Refer to Testing and

Accelerator pedal position sensor

Adjusting, "Fuel System Pressure - Test".

Power train data link

4. Ensure that the fuel system has been primed.

Refer to Testing and Adjusting, "Fuel System -

Camshaft position sensor

Prime".

Valve lash

5. Check for fuel supply lines that are restricted.

Recommended Repairs

6. Check the fuel filters.

Perform the following diagnostic procedures in

7. If the temperature is below 0 C (32 F), check

order:

for solidified fuel (wax).