AVM 249 Fuel Systems Test 1 Practice Test

Priming a fuel system means pushing fuel through the lines and pumps to purge air and establish fuel pressure so the engine can start reliably. Air in the lines can prevent the pump from building pressure and fuel from reaching the engine, causing hard starting or no start. By using a primer or manual/auxiliary pump, you force fuel through the system until the air is expelled and fuel is present at the pump and nearest fuel-distribution points, ready for normal operation.

This is done before starting the engine or after any maintenance that could introduce air (like opening the system, replacing filters, or servicing pumps), or after a pump failure, to ensure the system is fully charged with fuel. Cooling the fuel, replacing filters, or simply running the engine to test are not priming actions themselves, though priming may be required after filter changes or maintenance.