Hello all,
I have a 1981 300SD with 233k miles I have slowly been bringing back to ideal condition. Currently, I am trying to resolve an issue with excessive exhaust smoke. The smoke is grey in color and has no particular smell or taste other than typical diesel exhaust smell. At night , it is very visible in the headlights behind me when accelerating, cruising at 60+, and developing into a billowing cloud on heavy acceleration.
During the day, I can occasionally see wisps of smoked drifting by the car at idle but don't really see any while accelerating.
Thus far,
-Valve clearances adjust properly.
-New Timing chain and tensioner, original IP marks line up.
-Monarch nozzles 15k miles ago, balanced myself but only within 50 psi (perhaps an issue?)
-Turbo and wastegate verified working properly and producing boost within spec.
-Diesel Kleen with every tank, plus Diesel Purge every 3k miles or so.
-Fuel filters clean.

The car runs excellent idles smooth with plenty of power, but I cannot believe that nothing is wrong, no way a Mercedes smoked this much from the factory its very embarrassing driving at night...

I'm ordering some properly balanced #1930 injectors from Greazzer, but in the mean time any help appreciated!!

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-1981 300SD 242k, stock - sold @ 250k
-1994 Toyota Pickup 4x4 R150F 5 Speed, 5VZ V6 swap.
-2004 Volvo V70-R 2.5T

some possibilities are check the u bend from the air filter to the turbo for oil from the case ventilation system. also next time you do a valve job look at the valve stem seals thats one of the more likely ones. also check to make sure the induction system is all good (clean air filter, turbo making good boost, alda is hooked up right with no leaks). Hows your egr doing could it be stuck open? it might help if it suffered a mysterious BB lodged in some vacuum lines.

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1985 300D om617: 8mm M pump 175cc 5200rpm, holset he221w @ 30psi, large A2W ic, compounds on the way.
KD9AFT
A&P

I am not quite certain from your description if the injection pump is timed right. Marks line up is not a totally understandable description. Injection pump retarded could produce a little more smoke than normal.

Also try the car for an hour or so with no air filter installed if you did not put a new one in. As long as you do not use dirt roads. Defeating the egr is done by some but is probably not your issue other than not a bad ideal. I did not type that last sentence. So I will break my fingers as they got carried away.

This hits home with my 81 300sd as well. Mine has a bumpy idle when first starting in the morning and smooths out as I drive. Between the time I start it and it smooths out there is a good amount of excess smoke and when accelerating it is really weak until it warms up. I have found if I get it up to a higher speed for a few minutes it tends to blow out the smoke issue and then even out to what should be normal exhaust.

Mechanic is not sure what the issue is at this point as we have done the valve adjustment / reseating, Oil/oil filter change, fuel filter change (clean), New air filter and the injectors are all clean... Still trying to sort out the issue (timing chain is next on the list). other than that I am starting to run out of reasons for this issue.

just thought of something if you get a chance look at your glow plugs and prechambers pay special attention to the impingement ball in the PC directly below the injector pintle it can wear which hurts combustion.

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1985 300D om617: 8mm M pump 175cc 5200rpm, holset he221w @ 30psi, large A2W ic, compounds on the way.
KD9AFT
A&P

Being weak I take as being under powered? I had that issue with my old 300tdt until I put in new injectors. Before on a cold morning especially below freezing it would smoke and be way underpowered until warmed up.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

The oil drag is so high on the 616 and 617 engines a lack of power on a cold day initially I expect on 15-40 oil. Making sure the fuel system is in really good shape is probably job number one on these older cars.

Especially where that system has possibly had almost no maintenance over all the years unless it quits.

Most of it is pretty economical to do yourself. I also expect the concept that fuel filters are forever unless the car pretty much quits has real issues.

For example any air accumulating in the system when sitting overnight is going to be noticeable. Checking and refreshing the fuel system is not the best ideal in the colder weather as it take some time.

It also never hurts to do a compression check to find out what you have to work with.

Thanks for the responses guys,
I'm running the newer baffled-type vent crankcase hose to air cleaner, I've also re-sealed the air separator; both of these helped eliminate oil getting into the u-tube. Blow-by on the engine is minimal.
On a related note to the one post, I found the engine likes 5W-40 more than the recommended 15W-40 even in the summer time, oil has come a long way since the 80s!

The car is headed to the shop to have the IP timing checked. Then I will investigate the pre-chambers, the head was replaced 25k miles ago or so at which point pre-chambers were replaced as well (according to PO....)

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-1981 300SD 242k, stock - sold @ 250k
-1994 Toyota Pickup 4x4 R150F 5 Speed, 5VZ V6 swap.
-2004 Volvo V70-R 2.5T

I was not aware you did not do your own work. Wait for the replacement injectors and install them first before paying anyone to check the injection pump timing. The injectors may solve your issue.

after the process of elimination it seems it could be two things poor fuel atomization/combustion or insufficient air for clean combustion. your injectors could have crapped out (which is unlikely if you did them recently if they were imbalanced when you set the pop pressure mostly all it does is make the engine rougher especially at idle) or have bad PCs (again unlikely but possible as you said the head was recently changed usually you get nailing/knocking if they have failed) the only possibility then left is insufficient air for combustion. check your air filter try removing it for a short drive after the car is warmed up see if that helps. another thing to try is to temporarily disable the EGR remove the two vacuum lines near the turbo and see if it clears up (if it failed open it could allow too much exhaust into the intake restricting the available oxygen for combustion). mind you it could be a failure in the EGR valve itself. finally whats your oil consumption looking like? one of the main symptoms of worn out valve seals is excessive oil consumption and smoking (maybe the PO forgot to install new ones when changing the head)

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1985 300D om617: 8mm M pump 175cc 5200rpm, holset he221w @ 30psi, large A2W ic, compounds on the way.
KD9AFT
A&P

On the turbo engines the integrety of the intake valve seals may not be important other than adding blow by. They are under positive pressure much of the time from pressurized induction air. Many cars still have the original valve seals I suspect and very little oil consumption with signifigant miles. Even the non turbo engines have no intake vacuum compared to gas cars.

Now the gas engines are another story where oil can be sucked down those guides. The intake system operates under vacuum conditions where the diesel does not. There is little enticement for the exhaust guides to take oil either as they too never spend time under vacuum conditions. It seems to take something like a sheered off valve guide or really one quite loose to get much oil into the valve system on these diesels.

Probably fifty percent of valve seals on these cars are well worn originals. Changing them perhaps would make little difference. So when I look at some of these engines giving a quart a thousand miles in base oil consumption. Putting some oil into the breather I have wondered if at least part of that was worn valve guides causing a slight over pressuring of the engine driving the oil out. Mercedes always seemed to specify fairly tight stem to valve guide clearances than many brands.

Yes that sounds very similar to my situation. I have a local reasonable mechanic that does alot of my more major work (this car is my current daily driver so I can't have it out of commission too long) and when I brought up the injectors maybe causing this, they did not think that this was the issue - however they haven't started it on a cold morning

The one issue they thought it might be could be the priming valve - or perhaps the priming pump? I am slowly replacing all the worn part on this car but my approach always is the lower hanging fruit. Maybe I should push them to look at the injectors and replace as needed?

Also another question - I have not done a compression test yet, could this also possible be compression related?

Thanks in advance!

Primer pump, no. That would give you different symptoms.

Compression related, possibly.

A leak down test would be in order to find out about valve seal, compression issues.

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83 SD

84 CD

I've never found this chart helpful, but maybe it will help you.

Attached Files

Diesel Engine Smoke Explained table.pdf (72.0 KB, 237 views)

Thanks Frank!
The air filter I change every 7.5k miles, it's quite clean. The EGR is disabled. I've tried increasing the wastegate opening pressure to 10 psi which helped a small amount but I felt like that was more of a band-aid than fixing the real problem. I do not have to add oil in between changes ever since re-sealing the centrifugal separator and changing to the baffled type breather hose


Update, I had long since disabled the EGR by removing vacuum lines. I did not consider that the valve itself could be partially open. I will install a blocking plate ASAP and see if I notice a change.

__________________
-1981 300SD 242k, stock - sold @ 250k
-1994 Toyota Pickup 4x4 R150F 5 Speed, 5VZ V6 swap.
-2004 Volvo V70-R 2.5T