I have a 1984 300 turbo diesel with 150K on the odo. My mechanic noticed that the injection timing was off and suggested that on the last oil change he move it from 17 degrees to 24 degrees(stock). this required removing the pump since the adjustment was at its limit. Since this adjustment the car REALLY smokes. Not the clouds of billowing white that would indicate a blown head gasket but a diesel smelling blue white. The smoke is real bad at idle, bad at speeds under 35 and not readily noticeable at 75. We have done the following to remedy:clean injectors,
replace injectors,change injector pump,change EGR valve, replace air filter, check compression (uniform 24 when hot, uniform 22 when cold),drain and replace fuel, moved the timing back to 20 degrees. The valves have been adjusted regularly, the timing chain has been replaced some months ago. The engine has little blow by. The turbo was also checked to see if it was a bearing leak into the exhaust.
The car has not historically used much oil, about 1 qt in 1500 to 2000 miles. Fuel mileage when timing was 15 degrees was 21, at 17 degrees it improved to 23/ 24. I also just did a short test after getting it back from its last week with the mechanic where I filled the tank to the filler neck, drove on the freeway for 27 miles and overflowed the tank with .66 gal. This may have been caused by fuel heating but it was freezing outside.
Needless to say this has confounded both my mechanic who specializes in Benz diesels and his buddy at another Benz shop. The car is impeccable otherwise and I would like to be able to drive it without an obnoxious cloud following me around. Is there something that we have overlooked?
Parked in the meantime looking for an idea. Thanks for any feedback.
Steve Stepanek

Steve,
Here is a general statement for you from my diesel repair manual. It is probably obvious to you and all the pro's, but I will post it for reference.

Blue smoke indicates that engine oil is burning in the cylinders and may be accompanied by excessive oil consumption. Some conditions which should be considered are:

-cracked pistons
-worn or damaged cylinder walls
-stuck piston rings
-worn or broken piston rings
-failed valve seals or guides
-faulty crankcase vent
-oil level too high
-fuel in crankcase oil
-inaccurate dipstick (causing the crankcase to be overfilled)

Thanks for the response Patsy. I feel that the cracked piston theory is unlikely since the compression is good and smooth between the cylinders. I have also noticed that the "diesely smelling smoke" is greatest below 1000 RPM. If i hold my foot on the pedal to aboove 1000 the smoke largely disappears. Also noticed that there was a little bit of air in the prefilter (fuel) just before the injector pump. Could this cause problems? I have spoken with my mechanic about checking the return line to the tank to see if it was blocked. Still parked.
Thanks for your ideas.

As far as I remember, air in the prefilter doesn't contribute to smoke. May effect your acceleration with a little studder though... but long as you prime the prefilter it shouldn't matter if a little bit of air sits inside.

I've found smoke on my diesel when a) low oil level b) wrong oil composition added c) did not use my diesel catalyst after a refill. I think you are ok on all of these points so I am baffled as well. Sorry.

-SB

Right off the bat, I'll tell ya that my experience is not with Benz diesels. That said however all diesels I have seen with "smoking problems" have been related to these three areas. 1. Timing. You said the mechanic changed the timing, I would have him check it again. I have heard of internal advance mechanisims "hanging up" prompting the adjustment of timing only to free themselves up later thus changing the timing once again. 2. Wear. The rings are allowing too much oil to pass into the combustion chamber. Probably not the issue if the compression is good. 3. Injectors. Once they start to wear out they go downhill pretty quickly. Several times now I've seen mechanics swear up and down that the injectors aren't the problem, only to have a fresh set eliminate the smoke. Since it didn't smoke until the timing was changed, chances are it is something that occured due to that event. If the mechanic screwed it up, he should make it right? Just my 2cents, RT

I notice that you are in The Salt Lake area. Is it possible that you are getting a contaminated batch of fuel? Are you using RedLine's Diesel Fuel Catalyst, or 85+? Have you changed the oil and filter recently? And what kind of oil do you usually use?

And, Patsy, I was beginning to wonder what happened to you! have you just been lurking around the Diesel Discussion forum? I haven't seen you in the Tech Help forum at all...
And how come you don't have email and profile icons at the bottom of your posts? It's resolved now, but I wanted to email you with a question the other day!

__________________

Scott Longston
Northern California Wine Country...
"Turbos whistle, grapes wine..."

What method was used to time pump? If it was timed by drip method it is necessary to put throttle linkage to full throttle. It seems that when I have forgotten to do this I get an indication that it's retarded quite a bit, then I give myself a dope slap and recheck it to find it's really where it belongs. Hope this helps.

Silverbullet,
Oil level good as the oil was just changed (15-40). Oil from Diesel mechanic so I am assuming it is right, but I will double check. I have not ever used diesel catalyst in the fuel, but see it mentioned by LONGSTON as well, so I will have to do some research on this topic. I have seen other threads on this so I will look for them..

RThomas,
I had a lengthy discussion on this timing issue with my mechanic, and he said that it was a concern to him as well and he had checked the pulley for any looseness, and found none. I am assuming that the car which has good pep and reasonable mileage is timed near right.(However we have had a swing of 9 degrees from 15 to 24 and now back to 20. That being said it does seem to run well at all of those settings with better mileage at higher numbers). Is there another way to verify that the pulley has not shifted or to check and verify this issue? We also talked about the centrifical advance mechanism hanging up that would cause the timing to be off. We have not gone after that advance mechanism yet, but it is now on the list as well. Wear is possible but does not correspond to the good compression, low blow-by and lack of oil consumption. ( I have thought that I may try resleeving the engine, but I would feel foolish to resleeve and still have the problem). INJECTORS were checked and then replaced, so I am ruling that out. I was feeling that if the compression is borderline at low speed that it may cause incomplete combustion on one or two cylinders at idle, and either be OK or undetectable at higher engine speeds.

D Haner, thanks for the reminder about WOT on timing. I will discuss this with my mechanic. I am handy with a wrench but most of my experience is on gas engines including a crank up restoration of a 1961 220. I have not yet done diesel injector timing (i do have an article though) and thought that since this particular change required pulling the pump out that I would let the expert lead the way.

Thanks everyone for all of the suggestions, it will give me some things to test on the next go around.
Steve Stepanek