BREATHER AS 4N4668 - Caterpillar

Probable Causes
Fuel supply
Electrical connectors or power supply
No signal from the speed/timing sensor
Ignition system
Incorrect base timing
Excessive loadRecommended Actions
Fuel Supply
Verify that fuel is supplied at a sufficient pressure that is stable. Ensure 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 qualityCheck the fuel pressure. Confirm that the pressure is within specifications. 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.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 Electronic Control Module (ECM). Inspect the wires and the power relay. Check the power and ground connections. Refer to Troubleshooting, "Electrical Power Supply".No Signal from the Engine Speed/Timing Sensor
Make sure that the speed/timing sensor is installed correctly. Refer to Troubleshooting, "Engine Speed/Timing Sensor".Ensure that the timing wheel is correctly installed.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.Verify 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 Operation and Maintenance Manual, "Ignition System Spark Plugs - Replace".Incorrect Base Timing
Verify that the base timing is correct. Refer to Systems Operation/Testing and Adjusting, "Ignition Timing - Adjust".Excessive Load
Check that the load is not excessive. Reduce the load. If necessary, disengage the driven equipment and test the engine.