I saw something leaking from my ‘85 300TD so I looked underneath and noticed some wet spots on the fuel line forward of the rear axle. Also the idle has been getting a bit rough and sometimes when you step on the accelerator from a low speed you get nothing, almost like it has no fuel. I already changed the fuel filters. The car runs fine on the highway with plenty of power but coming home today up a steep hill 200 yards from my driveway the car slowed to 5 mph. Can a leaking fuel supply line cause air to be sucked into the system and cause these symptoms? I had an ‘81 Eldorado diesel last year with the exact same symptoms and after changing the rotted out section of line it ran fine. Can the bad section be replaced with fuel hose? It looks almost impossible to maneuver a new 10 foot section of fuel line over the rear axle area, at least if you only have ramps to raise the car.

Even from a small pinhole leak that may just drip down on top of a suspension member and evaporate before dripping to the ground??? That would mean thousands of cars that are 15 or 20 years old or older with rusty fuel lines and that are experiancing rough running and low power may have this problem and not even know about it. If it wasn't for my similar experiance with an Eldorado diesel I had, I would never have thought about it and would have wasted money with replacing injectors, the injection pump and who knows how much else!!!

A tiny hole will let in more air than it will let fuel out. If the hole in in the intake line it will suck air and it doesn't take much to cause big problems. If it's a hole in the return line then it won't cause running problems but it will hurt mpg. I don't see why you couldn't replace a bad section with rubber fuel line.