So, the faithful 850 wagon, owned for 5 years, never misses a beat..... 2 weeks ago, my beloved calls- car won't start. I drive down with a load of tools- she is right! It won't start! Blazing hot day, call AAA to get it home. Guy arrives, I tell him sounds like no fuel.... he gives me a look, gets hammer out of cab, slides under the rear....... whack! whack! under gas tank. Slides out, turns key....! Bingo! Car fires up! Magic way to free up aging fuel pump. Thanked him a lot, went home, ordered pump rebuild kit, filter and relay just for the heck of it. Replaced all last weekend- car running fine......until today...... car limped home, belching black smoke, losing power, won't keep running, but revs OK. First thought, bad new fuel pump, BUT.... if it is, why black smoke? Enough tailpipe soot to blacken rear of car. And I tried the Schroeder valve by the filter, seems plenty of gas there.... so, big question- by shaking up the fuel system and probably giving it more pressure than before with a new pump, what could I have stirred up that is causing bad running, and black smoke, like it is running very rich?????? Help!

 

Nothing at all to do with the fuel system that I just went through. The throttle cable was sticking on the drum, so I pulled off the cover to lube it, and, behold! The 2" or so hose directly below the throttle body that comes from the top of the radiator has slipped partially off! Adjusted, tightened the clamp, and all is once more good in Volvoville. I have no idea what that hose is for, but it needs to be there.

 

tough to follow your reference without looking under the hood but sounds like the preheater tube for the intake air or could be part of the PCV etc . Sounds like it was just making a big vacuum leak. Good work on the fix, vacuum leaks are sometimes difficult to track down.