I’m seeing a lot fuel leaking. I thought it was the return tube but I think it is leaking above it. I used a wrench and was able to snug the very top input line. It did not help. Any tricks to this ? Mike

If the nut has been snugged on the line for a time and not leaked, I would say the fuel injection hard like has cracked. Less frequent is for the fuel injection hard like to crack.

If you had your lines loose and retightened them it is possible to get crud between the seating area of the line and the injector.

If any of the line clamps are missing that increases the chances of a cracked line but rarely, they crack anyway.

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84 300D, 82 Volvo 244Gl Diesel

Fuel will creep, even upwards. How are your return lines? They can look ok and still seep at the nipple.

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (116k)
1991 350SD (206k)
1991 300D (228k)
2008 ML320 CDI (199k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)

Update. I’m a terrible mechanic. It was the hard to reach return hose facing the head under the throttle linkage I cobbled together from the 1980 body and 83 engine. Thanks all.

It may just be me but it is running better. Would a leaky return hose suck air into the lines and reduce fuel pressure somehow?

It'd be a lot easier if you'd post the year, model, and some photos.

Not ideal to ask an engine question without even stating what engine, year, and vehicle model, though amazingly common on car forums. Perhaps the same people who never use turn signals, but get angry when others don't know their intentions.

I have read of cracked fuel tubes, usually at that injector fitting. Can't repair, must source a good used tube. If not cracked and leaking at the metal-metal interface, there are copper or aluminum "soft-seals" used on similar AN flare fittings in aerospace. A small thin flat copper or brass washer might work.

To avoid any fuel seepage at the return hoses, try 1/8" Viton tubing like I did. The OE fabric wrapped rubber starts seeping after ~5 yrs.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans