Short answer
Work from the tank forwards. Fill the filters with clean fuel, open the first bleed point, operate the lift pump until fuel runs free of bubbles, close it, and repeat at each successive point. Many modern common-rail engines self-prime and must never be bled at the high-pressure side.
You will need: Spanners, absorbent pads, clean fuel, torch, waste container
A diesel will not run with air in the fuel. After a filter change, a tank run low or a leak on the suction side, bleeding is what gets it started again.
The principle
Air is pushed forward and out through bleed points in sequence, working from the tank towards the engine. Skipping a point or working out of order leaves a pocket that will stop the engine minutes after it starts.
The sequence on a mechanically injected engine
- Find and fix whatever let the air in. Bleeding a system with a leaking joint just refills it.
- Fill the primary filter bowl with clean fuel from a clean container.
- Open the bleed screw nearest the tank side of the circuit.
- Operate the lift pump — manual lever or electric priming — until fuel runs steady and free of bubbles, then close that screw.
- Repeat at the next bleed point, and the next, moving towards the engine.
- Start the engine and let it settle. Check every joint you opened for weeping.
Common rail is different, and this part matters
Never loosen a high-pressure line or crack an injector on a common-rail engine. Those systems hold fuel at pressures that can inject through skin and cause life-threatening injury, and pressure can remain after shutdown. Most self-prime or have a specific procedure in the manual. Follow it exactly. See mechanical vs common rail and can I service a common-rail engine myself.
If it will not stay running
Repeat air ingress points at the suction side: filter lid seals, a cracked hose, a loose fitting, a tank pickup above the fuel level in a seaway. See starts then stops.