Diagnostic Information for Lower End Engine Noise Regardless of Engine Speed - 8.1L (L18)

Important: Do not replace the engine assembly with a lower end engine knock or rattle type noise without inspecting the engine internally.

This bulletin is being published to aid technicians in the diagnosis and repair of a lower end engine noise regardless of engine speed. The lower end engine noise has been described as a piston, connecting rod and/or piston wrist pin type noise. This type of lower end engine noise will not change with the engine's temperature. Using a Tech 2®, the noise can be limited to the lower end of the engine by cancelling cylinders.

Important: During the repair, do not hone or re-finish the cylinder bores. Only properly clean and lubricate the cylinder bores before installing the new piston assemblies.

The technician, after verifying the lower end knock, should verify the engine build date. The label on the engine oil pan or valve cover will show a build range between T50301XXXX - T50429XXXX. The year is represented by the number 5. The month and day are represented by the 0301 (March 1st) through 0429 (April 29th). If there is excessive wear found at the piston or piston pin, all eight pistons will need to be replaced.

Important: If a piston pin has caused excessive scoring to the cylinder bore, the engine will have to be replaced. At this time, boring cylinders for oversize pistons is not suggested.

For repair information, use the following current SI Document Identification Numbers for the following procedures.

For vehicles repaired under warranty, use: