Conestoga Diesel Injection


1321 Byerland church Rd.

Willow Street PA, 17584-9776

Hours: Monday through Friday 8:00AM to 5:00PM

Phone 717-806-5561  FAX 717-806-5572

Fuel Line Routing 

Fuel injection systems deliver fuel to the cylinders for combustion.  However, that is not all they do.  They also use fuel as a lubricant, to keep the parts doing the fuel delivery, cool and lubricated.  This is why the quality of fuel has such a bearing on the longevity of fuel injection components.  Because these components use fuel as a lubricant, and for cooling, there is a constant flow of fuel in and around the components themselves, while they perform the intended function.  This fuel must be returned to the fuel tank, through the return fuel system.  This system consists of hoses and connecting parts, that carry the fuel away from the injection component, and back to the tank.  This includes injectors, and pumps.  

Ford/IH 6.9 and 7.3 engines utilize a unique system, which includes an O-ring and cap based containment system around each injector, and hoses to carry the fuel away.  This system creates an air tight seal, which not only prevents fuel from leaking out, but also prevents air from leaking in.  Because of the way the return line system serves as a removal mechanism for excess air in the supply fuel, and because of where the fuel tank and lift pump are located, the return line system is under vacuum when the engine is at rest.  This vacuum is needed to prevent drain-back of the fuel in the fuel filter, and is created by the weight of fuel held in suspension in the lines.  Any air intrusion into the fuel return system will create start, then stall with extended crank conditions, when the vehicle has been allowed to sit, typically overnight.  The O-rings on the injectors, and the plastic caps, are reliable until they have hardened by time, or excessive thermal cycling.  Typically these return line systems are very reliable until disturbed by nearby mechanical action, which may break the contact surface seal of any component in the vicinity.  Once a component is disturbed, it is time to service the entire O-ring and cap system.  This means replacing the O-rings, caps, interconnecting fuel lines and clamps, with new components.  However, the original routing of the lines may not need to be preserved, and you may also find yourself with slightly different components than what were on the engine originally.  

Our return line kits feature new Viton O-rings, caps, clamps and hose.  Sometimes depending on the application, additional hardware is required.  The below illustrations cover some of the more confusing installations.