Do I have to bleed fuel sys after return hose replacement?
 

I will be changing my badly weeping injector return lines soom. Will I have to then bleed the fuel sys?

No.




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Just R&R the hoses and be done with it?....

Yes.

bleed fuel system
 

I believe dkverou is correct. And you were wise to replace those return lines, I assume they are of the type with the "cloth weave" outer skin, which fail and leak with age, plus, since fuel seeps out under pressure, air seeps in when the engine is shut down and fuel pressure drops to zero.

Not EXACTLY..........You could dribble the return fuel straight on the ground...restart would be no problem.........return fuel is routed directly back to the tank.(Via banjo fitting on filter.)
The injectors spill diesel, not injected into the engine, into the return ports...this part of the fuel system is not pressurised and no air can get back in to the pressure or supply side of injection system. The filter assembly is pressured by the injection pump's own lift pump and will push any air out the top of the filter too.
The return banjo bolt on filter top will allow some air to enter the main fuel filter but due to a supply/return restrictor in the filter housing, fuel will still go to the IP under pressure.............of course, you'll run out of fuel real quick like this !


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bad info
 

Sorry for the incorrect info. Thank you for correcting.

check this out: http://dieselgiant.com/mercedesfuelhoseinstall.htm

Just throw on the new crack free lines and enjoy. :)