PLUG-ORIFICE 6Y9437 - Caterpillar

Probable Causes
Inlet air restriction
Exhaust restriction
Incorrect ignition timing
Fuel supply
Governor and linkage
Exhaust bypass
Incorrect valve lash
Ignition system
Turbocharger
Cylinder compressionRecommended Repairs
Inlet Air Restriction
The maximum allowable inlet air restriction is 3.75 kPa (15 inches of H2O). If the indication is higher than the maximum permissible restriction, clean the filter element or install a new filter element. Check the restriction again. If the restriction remains too high, inspect the air inlet piping for obstructions.Exhaust Restriction
The maximum allowable exhaust restriction is 6.7 kPa (27 inches of H2O). Check for restriction in the exhaust system.If the difference between the pressure at the exhaust elbow and the atmospheric pressure exceeds the specification, determine the cause. Make the necessary repairs.Ignition Timing
Note: Data from a fuel analysis is required for this procedure.Use an electronic service tool to check for the correct desired ignition timing. Compare the timing to the recommended timing in the Engine Performance, "Fuel Usage Guide".Adjust the ignition timing according to the recommended timing in the Engine Performance, "Fuel Usage Guide".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, balance line, gas shutoff valve, fuel valve and actuator for the fuel valve. Verify that the system's components are operating correctly.Replace the fuel filter, if necessary.Inspect the gas pressure regulator's diaphragm for leaks. Make sure that the valve moves freely. The valve must seat correctly.Make sure that the balance line is secure. Inspect the balance line for plugging.Inspect the actuator and the linkage. Make sure that the linkage operates smoothly for the full range of travel. The linkage must have no free play. Adjust the actuator and the linkage, if necessary.Governor and Linkage
Inspect the linkage between the governor and the carburetor. Make sure that the throttle operates smoothly for the full range of travel. The linkage must have no free play. Lift the linkage to the upward position and release the linkage. The linkage must drop freely. Adjust the governor, the linkage, and the carburetor, if necessary.Exhaust Bypass
Make sure that the exhaust bypass valve can move properly. Inspect the diaphragm, the exhaust lines, and the connection to the inlet manifold for leaks. Make sure that the breather is not plugged.Valve Lash
Check the valve lash according to Testing And Adjusting, "Valve Lash and Valve Bridge Adjustment".Ignition System
Inspect the ignition transformers for the following conditions:
Loose connections
Moisture
Short circuits
Open circuitsInspect the primary wiring and the secondary electrical connections.Make sure that the correct transformers and spark plugs are installed. Inspect the extenders for signs of pin holes and arcing.Maintain the spark plug according to the engine's Operation and Maintenance Manual.For troubleshooting the electronic ignition system, refer