I replaced the CCV on my M54 3.0 last week. Once I got the old CCV out and opened for inspection (i.e. destroyed) I found that the valve itself was probably OK, although I can't be certain. My "for sure" problems were these.
First
The heavy power lead running from the alternator to the starter had worn a hole in the drain hose. In other words, a sizable vacuum leak through the CCV system. It appears that some work was done before I bought the car & this heavy cable was positioned so it rubbed on the hose just at the CCV connection where the abrasion wore a hole.
I was careful to route the alternator cable away from a rubbing point at the CCV connection during re-assembly. Even if the cable does flex and droop over time it will move to contact the drain hose in a location away from the joint where it won't have a hard rubbing point to abrade.
Second
The drain hose and drain in the dipstick guidetube were plugged solid. In my case, I was able to remove the drain hose from the dipstick guide tube while in place. I used a small screwdriver pushed into the slip joint & ran it all the way around the circumference to break adhesion, then pulled the hose up & off the guidetube. It was the only hose that didn't crumble when disturbed during CCV removal.
From my experience, it would have been possible to remove this drain hose and dipstick guide tube for cleaning &/or replacement without replacing the entire CCV system.
I had terrible idle quality, 10 lean & mis-fire codes & the CEL lit. Crankcase vacuum was 100 mbar vs the spec of 10 to 15. I also had a new intermittent burnt oil smell in the engine bay with a wisp of smoke off the rear bank exhaust manifold, but no obvious smoke out the tailpipe, which I found puzzling with high crankcase vacuum rather than pressure. I'm baffled by the high crankcase vacuum given the leak in the crankcase side of the CCV system although this vacuum leak does explain the idle quality, codes and CEL.
Anyway, idle is again so smooth that I have to check the tach, all the codes are gone & the burnt oil smell is no more.
Sorry for the lack of "in place" pictures. By the time I found these problems my hands were so grimmy with oil muck that I didn't dare pick up the camera.
Regards
RDL
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