ALTERNATOR AS 4812594 - Caterpillar

Probable Causes
Fuel quality
Pistons
Valve lash
Electronic unit injectorsRecommended Actions
Fuel Quality
Check the fuel quality. Refer to Systems Operation, Testing and Adjusting, "Fuel Quality - Test".
If unsatisfactory fuel is found, perform the following procedure.
Drain the fuel system.
Replace the fuel filters. Refer to the Operation and Maintenance Manual, "Fuel System Primary Filter (Water Separator) Element - Replace" and Operation and Maintenance Manual, "Fuel System Filter - Replace".
Fill the fuel system with fuel that meets the standard in Operation and Maintenance Manual, "Fluid Recommendations".
Prime the fuel system. Refer to Operation and Maintenance Manual, "Fuel System - Prime".
If the fault is not eliminated, refer to "Pistons". Pistons
Inspect the pistons for damage and wear. Replace any damaged parts.
If the noise is still apparent, refer to "Valve Lash". Valve Lash
Refer to Troubleshooting, "Excessive Valve Lash".
If the fault has not been eliminated, proceed to "Electronic Unit Injectors". Electronic Unit Injectors
With the engine speed at a fast idle, use the electronic service tool to isolate one cylinder at a time. Note if there is any reduction in engine speed. If a reduction in engine speed is not noted, the isolated electronic unit injector is not operating under normal conditions. If the isolation of a particular cylinder results in a reduction of engine speed that is less than normal, this may indicate that the electronic unit injector is operating below normal performance.
Remove the electronic unit injector from the suspect cylinder. Refer to Disassembly and Assembly, "Electronic Unit Injector - Remove".
Install a new electronic unit injector. Refer to Disassembly and Assembly, "Electronic Unit Injector - Install".
Repeat the test in 1. If the noise is still apparent, remove the replacement electronic unit injector and install the original electronic unit injector. Refer to Disassembly and Assembly, "Electronic Unit Injector - Remove" and Disassembly and Assembly, "Electronic Unit Injector - Install".
If the fault is still apparent, refer to Troubleshooting, "Mechanical Noise (Knock) in Engine".