Which pump is used to supply fuel to the engines during start?

• A. Transfer pump
• B. Boost pump
• C. Main pump
• D. Prime pump

Answer: (D)

Priming the fuel system is what happens when you prepare an engine to start by ensuring fuel is delivered to the injectors and control unit from the moment you begin cranking. The pump used for this is the prime pump. It is specifically designed to push fuel through the lines, fill the pumps and lines with fuel, and expel any air so that when starting begins, fuel is already present at the fuel control unit and injectors. This makes ignition reliable right away and prevents vapor or air pockets from hindering start-up. The main pump provides the normal, continuous fuel supply once the engine is running, so it isn’t the component used primarily for starting. The transfer pump moves fuel from storage to the fuel system and is not dedicated to engine start, while the boost pump maintains pressure during operation or after start if needed, but the priming action is the prime pump’s main job.