The Cummins turbo-diesel is a popular light-duty diesel engine which was available in the Dodge Ram, as well as in some commercial vehicles and motor homes. If your Cummins diesel runs out of fuel, or if you have changed the fuel filter, air will enter the Cummins fuelling system, requiring the system to be bled of air in order to function properly. Air in the system can manifest itself in very hard starting, poor idling, and smoke from the tailpipe. Earlier model Cummins turbo-diesels require a manual bleeding, while later era Cummins diesels have an automated bleed procedure.
Make sure the truck engine is cool before bleeding the system. If your Cummins is a 1997 or earlier model, there is a hand primer located on the lift pump, which is located below the fuel filter on the driver's side of the engine block. It will be a tab that you can work back and forth.
Open the bleed screw above the fuel filter and pump the hand primer until fuel comes out of the bleed screw. Catch the spilling fuel with rags or a small bucket. When you notice no air bubbles in the fuel, close the bleed screw. You may want to perform this procedure a few times over the course of a few days to purge all the air from the system.
Turn the ignition to the "On" position and allow the electric lift pump to cycle if your Cummins in a 1998 or later model. When you turn the key to the "On" position, the lift pump will cycle for about 30 seconds, during which the system is refilling the fuel canister. Repeat this process three times to purge as much air as possible from the system.
Filling a fuel filter with diesel fuel before installation can reduce the amount of air that will need to be purged from the system.