GUIDE 8V4028 - Caterpillar

Probable Causes
Cold cylinder
Electrical connectors or power supply
Ignition system
Incorrect base timing
Fuel supply
Incorrect air/fuel ratio
Incorrect governor adjustment
Air inlet restriction
Exhaust restriction
Incorrect valve lash
Cylinder head and related components
ThrottleRecommended Repairs
Note: If the symptom only occurs under certain operating conditions (high idle, full load, engine operating temperature, etc), test the engine under the conditions. Troubleshooting the symptom under other conditions can give misleading results.The Caterpillar Electronic Technician (ET) and the Integrated Temperature Sensing Module (ITSM) can be used to detect a misfiring cylinder. Use the following procedure:
Use the "Data Link/Select ECM" option on the Cat ET to select the ITSM.
Select "Diagnostics/Diagnostic Tests".
Select the suspect cylinder and click the "Start" button in the lower left corner of the screen. Cat ET will display a graph of the cylinder's exhaust gas temperature. The output voltage of the transformer's secondary circuit, the engine speed, and the desired engine speed are also displayed.Cold Cylinder
Locate the misfiring cylinder. Check the following components for failure: spark plug, extender, ignition transformer and primary wiring. Inspect the extender for signs of pin holes and/or arcing.Refer to Troubleshooting, "Ignition Transformers Secondary Circuit and Spark Plugs".Electrical Connectors or Power Supply
There may be an intermittent interruption of power. Check the wiring harnesses and the connectors. Inspect the connectors in the terminal box. Inspect the battery connections and the ground.Inspect the wiring from the battery to the control modules. Refer to Troubleshooting, "Electrical Power Supply".Ignition System
Inspect the ignition transformers for loose connections, for moisture, for short circuits, and for open circuits. Inspect the primary wiring and the secondary electrical connections.Make sure that the correct transformers and spark plugs are installed. Inspect the extenders for signs or pin holes and arcing.Maintain the spark plug according to the engine's Operation and Maintenance Manual.Check the Base Timing
Verify that the base timing is correct. Refer to Systems Operation/Testing and Adjusting, "Ignition Timing - Adjust".Fuel Supply
Make sure that fuel is supplied at a sufficient pressure that is stable. Make sure that the size of the fuel line is sufficient. Inspect the fuel system for leaks.The following conditions can cause the engine to malfunction:
Low fuel pressure
High fuel pressure
Poor fuel qualityMake sure that the fuel pressure is correct. When possible, interview the operator in order to determine if fuel quality is in question. Try to determine if the source of the fuel was changed.Inspect the fuel system components: fuel filter, gas pressure regulator, gas shutoff valve and fuel metering valve. Verify that the system's components are operating correctly.Replace the fuel filter, if necessary.Air/Fuel Ratio
An air/fuel mixture that is too rich or too lean will have an adverse effect on engine operation. Verify that the exhaust emissions are correct. Refer to Systems Operation/Testing and Adjusting, "Air/Fuel Ratio Control - Adjust".A change in the fuel energy content will change the air/fuel ratio. Obtain a fuel analysis.The fuel supply pressure must be adequate and stable.Governor Adjustment
The governor's parameters must be programmed with the values that provide stable operation. Refer to Systems Operation/Testing and Adjusting, "Engine Governing - Adjust".Air Inlet Restriction
The maximum allowable air inlet restriction is