This is a general diesel fuel question: I have a problem with (I think) fuel leaking back to the tank from the lift pump. Engine will light right up if I start it every few days, but If I let it go a week or so, I have to crank and crank it. If I hand prime the lift pump it starts right up. I'm thinking fuel is draining back to the tank as there are no external leaks. I'm not sure about how to go about putting a vacuum test on the various components. Suggestions???
Doesn't sound like a fuel leak if you can operate the manual primer and it fires right off. Could be the check valves in the lift pump are failing and allowing fuel to drain back to tank over time. If you have a manual shut off on fuel tank that you could close, allow the machine to sit for week or so, then open fuel valve. If machine fires right off it would give some confirmation that lift pump check valves are faulty.
Ugh, Willie, you just said you were disagreeing with him, while you were agreeing with him?? :beatsme Like Willie said, it's usually a check valve in the lift pump, but if you said what machine and engine it was, somebody would probably know where the check valve was.
Well, I'm referring to the thread title mitch, "fuel line leak". Not saying there is or is not one, just saying if fuel line were actually leaking, even working the manual primer would be iffy starting it up. Sounds more like fuel flowing back to tank via faulty lift pump. But as you said, what machine it is makes a big difference.
Yup, lift pump/leak back problems can be tricky to diagnose..with out throwing parts at it. Depending on what engine we are talking about determines where to start and how much its gonna cost. IF its an "inline pump" the overflow valve could be a culprit as well as a lift pump.
Machine is actually an old Ford Louisville with an Ford inline 6 diesel. Originally, I suspected check valve(s) in the lift pump, but the cost of a new pump is somewhat prohibitive (as in throwing new parts at it). Priming with the hand pump takes 50 or more strokes and cranking with the starter takes longer than I care to grind away. Suffice to say, when the problem first arose, I cranked for minutes and did not suspect a fuel issue as the truck had set for months without running. My original thought was the shut off solenoid was stuck, but that was disproved when I looked closer. Thanks for your thoughts...
Not sure if its a hardline from the lift pump to the injector pump but would a pressure gauge after the lift pump show the leakdown? If you pressurize by hand and wait say a few minutes, then pump it again by hand what should the results be? can the system bleed through the injector pump/injectors like a self prime or should the pressure / resistance to pumping still be there after a few minutes?
you could take the primer out and see if the diaphragm is ripped. if it is, it can allow fuel to leak back to the tank making it act like yours is.