GM-45873-100 allows the fuel return volume to be measured on 5.2L and 7.8L medium duty truck diesel engines. It consists of additional hose assemblies and connectors to allow a technician to measure the fuel volume from each cylinder, a set of graduated cylinders, and hoses to measure the pressure regulator and pump return systems. Using GM-45873-100 will allow more precise measurement of the fuel return system to assist in diagnosing driveability concerns, and prevent unnecessary parts changing or increased warranty due to incorrect diagnosis.