What is the proper procedure to purge air from a fuel system after maintenance?

• A. Prime the fuel system and bleed air at injectors or purge valves, start at low speed, and confirm continuous fuel flow with no air pockets
• B. Bleed air only at the tank and start at high speed
• C. Dispose of contaminated fuel and restart
• D. No purge is necessary for system maintenance

Answer: (A)

The essential idea is to remove trapped air from the fuel system by priming and actively bleeding the lines at the highest points where air collects, such as the injectors or purge valves. By pushing fuel through these points, air pockets are forced out until you see a steady stream of fuel with no air bubbles. Starting the engine at a low speed then lets the fuel pump bring the system up gradually without rushing, ensuring the pump can keep pushing fuel and continue purging as pressure builds. The goal is to confirm continuous fuel flow and a fully purged system with no air pockets, which prevents misfiring, rough running, or fuel-starvation.

Bleeding only at the tank would not remove air trapped in higher sections of the lines or at the injectors, and starting at high speed can introduce or trap air, possibly stressing the pump. Disposing of fuel or skipping a purge altogether doesn’t address the need to remove air from the system after maintenance.