How to Bleed Fuel System and Change Fuel Filters? How to bleed fuel system. Sometimes the fuel can back flow from the delivery hose and this would result in excessive air in the system and not allowing you to use the manual pump to pump the fuel back up. Remove the fule filler cap and apply low air pressure to force the fuel forward to the filter. What to Do If You Run Your NPR or NQR 4HK1 Diesel Engine 1) Put at least 5 gallons of good, clean, on-road diesel fuel back in the fuel tank. 2) Locate your fuel primer pump on the fuel filter housing, also locate the fuel rail on the engine (you will need to flip the cab forward to access the engine) Loosen bleeder bolt on priming pump. Pump till fuel comes out.