This document provides instructions for removing and installing various components of a Caterpillar C9.3 engine, including the combustion head, ARD nozzle heater relay, ARD fuel solenoid valve, exhaust manifold, and exhaust elbow. The procedures describe disconnecting electrical connections and fluid lines, removing fasteners, and installing replacement parts in the reverse order of removal while applying sealants and lubricants as specified. Safety precautions are provided regarding working on hot or high voltage components and preventing fluid contamination.