I'm tossin up the white flag here on my 1999 e300td and am hoping for so advise on my nailing issue. Car was running quite and smooth but had a few delivery valve seals leaking, so I replaced seals and while I was in there, glow plugs, shut off valve oring, all plastic fuel lines, and what the heck, the crank sensor as I was staring right at it. Car started up after a little bit of cranking and smoothed out and ran quite with no leaks. Great! job well done. After a few thousand miles, it started getting noisier and nailing. First only when it was cold, then it wouldn't even clear up when it was hot. Said nailing occurs a bit at idle, gets worse under light throttle till around 1400 rpm then goes away. Car runs great other wise. I double checked my work, researched the issue to death, tried to ignore it, thought it would go away after some more miles. I ran a ton if injector cleaner with cetane boost, no help. So I started poking around again. I have air coming out of the bottom of the pre filter housing line ( the little screen before main filter ). Great I thought, this was the issue. But I had replaced the lines, prefilter ect with he seal job so I was kinda baffled. So I went to work trying to get rid of said air. Ordered another prefilter and orings for lines. Still have air. Ordered a oem pre filter, new filter housing and orings. Still air. Still nailing and now running a bit rough with smoke when cold under light throttle. So like an idiot, I pivot from the air in the line issue and start thinking it must be something else, something more serious. Valve seat recession, bad injectors, ect. In a moment of bad judgement I load the parts cannon, with 286K on it, no history of injectors being touched I go for it. I order injectors, lift pump, shut off valve, fuel thermostat, new hard lines, and decided to redo my delivery valve seal job, this time using the 30nm release, 30nm release tq to 35 nm method I read about here as well as change the springs. The plan was to replace the delivery valves too, but they are discontinued from MB. Also do a compression test, ( came back strong ) as well as run with intake off looking for smoke from inlet ports, no smoke seen. So I install my mess of parts as well as new fuel lines and tank screen and think no way I don't have this licked. My wallet is now lighter but my om606 will be singing its normal sweet music. Nope. Still doing it. Matter fact its worse to some degree. And I am reminded that I still have air coming out of the bottom of the prefilter. None before it for sure, but I cant seem to get rid of it. So any ideas fellas? think the air is causing this issue? something else I should look at? I apologize for the long winded rant. Maybe its therapeutic in some way.

Some of the folks at super- turbo diesel have talked about this very issue with the om606 fuel pump (probably applies to 603 and 617 pumps, as well) due to a faulty original design - the pump essentially tries suctioning an amount of diesel that the lines can't keep up with which causes cavitation (diesel fuel getting vaporized into bubbles). Those cavitation bubbles don't dissolve back to liquid on their own however, and end up getting compressed by pump, delaying timing and causing rough running.

One remedy I heard was to reduce any restrictions in fuel lines via taking out extra bends ... or to just installing a large 8mm fuel supply line all the way from prefilter to tank!
Here's some discussion about it:

*extra*turbodiesel-dotcom/std/showthread.php?tid=3863

(^--replace *extra* with super , & -dotcom w/ .com)

I've got an OM603 that didn't pass emissions, is nailing, smoking at times and I was about to do the same thing - rebuild injectors and start replace things. I've noticed the bubbles as well though, and hearing about your issue and reading the link has me thinking it could be the same source problem. May have to also check into a larger / smoother supply line.

Good luck - will be interested to learn what you find out.

Thanks for the reply. In my research I've read about this too. I think there was a guy with a om606 G Wagon that talked about this issue and added a inline pump back by the tank to help with this issue. I think this is a legit theory and I thought about adding a pump, but held off for the reasoning that it ran well for so long, then degraded to what it is now. Maybe I'm just being stubborn in thinking it should run well in OEM configuration

The bubbles will and do cause the nailing , I ran an om606 on veg oil and biodiesel so quite used to it.
I would suggest the lift pump is maybe trying to move / shift too much fuel ? , more than engine needs possibly / more than it should be doing.The excess will run back to tank anyway but the suction on the fuel in line suffers the cavitation.

quick update to this. I gave it a few hundred miles to settle in. Still not running any better. But I poked around some, performed injector cut out test, nailing is most sever from cylinder two. While I had hoped that my irresponsible parts party would have solved this, it did solve my idle lope/hunt on slow speed coasting. I believe this was due to a failed shut off valve. When I replaced it, diesel was leaking out of the electrical plug. It also is running better then ever at speed. I read up more on delivery valve seal replacement, this time widening my search to any diesel that would pop up ( not just om606. And of course, its a common issue. lots of theory's as to why. One that that made most sense to me was a quick video on YouTube, stating it recommends torqueing the valves to 50nm. His thought is the old valves need a bit more to seal. I may try this, but Id also like to replace the valves and holders too. Both of these parts are NLA from Mercedes. Any one know of a source for these?

One other question as to the air coming out of the pre filter, any one try stacking two orings on the filter before install? I thought I read something in a post about that last night

I am not sure about using 2 o-rings on the small strainer fuel filter. One new correct sized o-ring has always worked on my 97 and 99 E300D’s.

__________________
Greg

Current
2005 E320 CDI (50k) W211 with OM648
1999 E300D Turbo (133k) W210 with OM606.962
1997 E300D NA (170k) W210 with OM606.912
1991 300D 2.5 Turbo (199k) W124 with OM602
1990 300D 2.5 Turbo (170k) W124 with OM602

it has worked on my 1995, 1996 om606s too. Never had air issues on those cars. The 1999 was air free too. Only replaced lines as because I was there for delivery valve seals and glow plugs. But i have a decent amout of air coming out of the bottom of the pree screen housing. nothing coming out of fuel thermostat to top of screen. Tried new orings, new filters, new filter housing. Even put the old line from fuel t stat to pre filter back on to try that. Still air. Not much at idle, but raise rpm and its pretty bad.

I would double up on the small o rings on pre filter on my 97 om606 as running veg oil mixes it would pull air in at that joint , the two o rings cured that.