SPOOL AS-RELIEF 2P4538 - Caterpillar

Probable Causes
Vibration damper for the C6.6 engine only
Engine supports
Low compression (cylinder pressure)
Individual malfunctioning cylinder
Electronic unit injectorsRecommended Actions
Vibration Damper for the C6.6 Engine Only
Check the vibration damper for damage. If necessary, install a new vibration damper. Inspect the mounting bolts for damage and/or for wear. Replace any damaged bolts. Refer to Disassembly and Assembly, "Vibration Damper and Pulley - Remove" and Disassembly and Assembly, "Vibration Damper and Pulley - Install".Ensure that the repairs have eliminated the fault. If the vibration is still present proceed to "Engine Supports".Engine Supports
Check for any of the following conditions:
Loose engine supports
Loose mounting brackets or broken mounting brackets
Loose bolts
Omitted bolts
Make all necessary repairs. Ensure that the repairs have eliminated the fault. If the vibration is still present proceed to "Low Compression (Cylinder Pressure)".Low Compression (Cylinder Pressure)
Perform a compression test. Refer to Systems Operation, Testing and Adjusting, "Compression - Test ".
If low compression is noted on any cylinders, investigate the cause and rectify the cause.Possible causes of low compression are shown in the following list:
Loose glow plugs
Faulty piston
Faulty piston rings
Worn cylinder bores
Worn valves
Faulty cylinder head gasket
Damaged cylinder head
Perform all necessary repairs.
Ensure that the repairs have eliminated the fault.
If the repair does not eliminate the fault refer to "Malfunctioning Individual Cylinder".Malfunctioning Individual Cylinder
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 cylinder 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 cylinder is operating below normal performance. Investigate the cause of the fault on any cylinder that is not operating. Investigate the cause of the fault on any cylinder that is operating below normal performance.
If all cylinders have been checked and no faults were detected 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 fault 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, repeat this test procedure from Test Step 1.