A replacement of fuel supply lines, fuel filters, fuel injection pump, high pressure fuel lines and injectors will let
air enter the fuel system. Follow the specified procedure to bleed the air from the system.
Since the fuel transfer pump provides a positive pressure through the fuel filter and fuel supply line to the fuel
injection pump, loose connections or defective seals will show as a fuel leak.
The most common place for air to enter the fuel system is between the inlet of the fuel transfer pump and the
suction tube in the fuel tank. Fuel tanks that have the fuel outlet fitting at the top will have a suction tube that extends down in the tank. Cracks or pin holes in the weld that joins the tube to the fitting can let air enter the fuel system.
Air in the fuel system will make the engine: hard to start, run rough, misfire, produce low power, and can cause
excessive smoke and a fuel knock.
The pressure relief valve arrangement on the Bosch P7100 fuel injection pump in the supply side of the fuel circuit
creates a self-bleeding system for air introduced during replacement of the supply side components.
Small amounts of air can be bled from the pump by operating the hand primer on the fuel transfer pump or by
cranking the engine.
The Bosch P7100 fuel injection pump has a jump-over tube to route return fuel and entrapped air from the pressure relief valve directly to the supply tank.
The Nippondenso EP-9 in-line fuel injection pumps will require additional venting prior to initial start-up, pump
replacement, or if the engine has been allowed to run out of fuel.
