Idle smoke 300sdl

[pilot53]

I have an 86 300SDL om603 with 75k miles. The engine is putting out some light grey smoke on idle and i'm trying to eliminate that. When the engine is cold there is a slight lifter tick from time to time, but it runs very smooth and starts easily, but does idle rough for 15 seconds if I don't let it glow extra time. The car is in great shape and well cared for, what could be causing this smoke? the heads not cracked, no cold pressure, runs at a needle width above 80c under load and I have checked the coolant for combustion gas with a test kit.

[mannys9130]

The injectors most likely need to be rebuilt.

[bsmuwk]

I'm curious, considering your mileage, does your car still have the trap ox still installed?

Rough idle for the first few seconds on a cold start is telling me you have a weak or failed glow plug. Replace the plugs and ream the prechambers of soot. Every one of my 603s and 606s kicks over instantly and settles into a smooth idle on start up - EVEN with ambient temps near 0* F.

For ticking lifters, run half a quart of trans fluid in the crank case 50 miles before your oil change and a few good highway runs with it @2.5k - 3k rpm. Your lifters are probably plugging up and aren't pressurizing properly. That low of mileage is just screaming "I'm rarely driven, help me breathe". Trans fluid treatment won't be an overnight miracle, takes time.

If I was bored and trying to eliminate some minute idling smoke (unburnt fuel) here's how I'd start (considering your mileage):

- Diesel Purge a hot engine (or run a mix of 70% kerosene/30% diesel )
- Get your injectors serviced (pop tested, cleaned, etc)
- Check, set injection timing


See what happens from there. I'm assuming you're keeping up with fluid, filter changes throughout the car.

[pilot53]

Originally Posted by bsmuwk

I'm curious, considering your mileage, does your car still have the trap ox still installed?

Rough idle for the first few seconds on a cold start is telling me you have a weak or failed glow plug. Replace the plugs and ream the prechambers of soot. Every one of my 603s and 606s kicks over instantly and settles into a smooth idle on start up - EVEN with ambient temps near 0* F.

For ticking lifters, run half a quart of trans fluid in the crank case 50 miles before your oil change and a few good highway runs with it @2.5k - 3k rpm. Your lifters are probably plugging up and aren't pressurizing properly. That low of mileage is just screaming "I'm rarely driven, help me breathe". Trans fluid treatment won't be an overnight miracle, takes time.

If I was bored and trying to eliminate some minute idling smoke (unburnt fuel) here's how I'd start (considering your mileage):

- Diesel Purge a hot engine (or run a mix of 70% kerosene/30% diesel )
- Get your injectors serviced (pop tested, cleaned, etc)
- Check, set injection timing


See what happens from there. I'm assuming you're keeping up with fluid, filter changes throughout the car.

Thanks, already ran 2 cans of diesel purge through the system using an external fuel tank, didn't make the slightest bit of a difference. Do your early 603 start that easily, even without afterglow? Too bad I just changed the oil or i would have liked to try trans fluid. Is it likely that i need to balance or change the nozzles at such low mileage? I haven't checked timing yet as I cant afford to buy an a-b light yet, i'm hoping that not the issue although the owners manual says to check timing at 30k miles and I have no way of knowing if that was done by the original owner. i also read that the lift pump can cause idle smoke, but would think that would lead to rough running under heavy load, which i don't have, but the engine did stall after changing the fuel filters. How can i test the lift pump?

[bsmuwk]

Originally Posted by pilot53

Thanks, already ran 2 cans of diesel purge through the system using an external fuel tank, didn't make the slightest bit of a difference. Do your early 603 start that easily, even without afterglow? Too bad I just changed the oil or i would have liked to try trans fluid. Is it likely that i need to balance or change the nozzles at such low mileage? I haven't checked timing yet as I cant afford to buy an a-b light yet, i'm hoping that not the issue although the owners manual says to check timing at 30k miles and I have no way of knowing if that was done by the original owner. i also read that the lift pump can cause idle smoke, but would think that would lead to rough running under heavy load, which i don't have, but the engine did stall after changing the fuel filters. How can i test the lift pump?

Absolutely, none of them have ever had any problems at or near 0*. There was a time where an 87 W124 wagon I had gelled up its fuel system and wouldn't start - though I believe ambient was -15* that night. Cold up in the Northwoods!!!

Low mileage isn't a saving grace for anything - the way I see it, that's a lot of time for that car to either A) not have been driven, gumming everything up or B) being driven quite a bit at short distance, which is worse than A as it never gets a chance to clear itself out.

My recommendation is to service the injectors every 70-80k miles. Not necessarily replacing nozzles, but giving them a thorough cleaning. Mercedes/Bosch dealers had a brass service set that cleared out any carbon in the nozzles. Definitely worthwhile to do, or rather, have done by those equipped.

You don't need an RIV light to check timing. I have one, and sure, it's nice, but with a little more time a lock tool (available for around $30 on ebay) will do the same job in letting you know where the pump is in time.

I've never heard of the lift pump causing idle smoke, it just supplies the system with fuel. The engine WILL stall when changing the filters, Mercedes never implemented a way for the system to purge air when changing the filters - which can only done by continuous cranking. If your engine is running, chances are your lift pump is perfectly fine.

How often does the car see full throttle? Believe it or not, it helps the engine rid itself of excessive carbon build up that otherwise wouldn't be blown out with normal putting around. If it's smoking dark black at full throttle and won't do it again after, you need to full throttle more often.


Sent from my toilet paper phone because it's a piece of shi....

[pilot53]

Originally Posted by bsmuwk

Absolutely, none of them have ever had any problems at or near 0*. There was a time where an 87 W124 wagon I had gelled up its fuel system and wouldn't start - though I believe ambient was -15* that night. Cold up in the Northwoods!!!

Low mileage isn't a saving grace for anything - the way I see it, that's a lot of time for that car to either A) not have been driven, gumming everything up or B) being driven quite a bit at short distance, which is worse than A as it never gets a chance to clear itself out.

My recommendation is to service the injectors every 70-80k miles. Not necessarily replacing nozzles, but giving them a thorough cleaning. Mercedes/Bosch dealers had a brass service set that cleared out any carbon in the nozzles. Definitely worthwhile to do, or rather, have done by those equipped.

You don't need an RIV light to check timing. I have one, and sure, it's nice, but with a little more time a lock tool (available for around $30 on ebay) will do the same job in letting you know where the pump is in time.

I've never heard of the lift pump causing idle smoke, it just supplies the system with fuel. The engine WILL stall when changing the filters, Mercedes never implemented a way for the system to purge air when changing the filters - which can only done by continuous cranking. If your engine is running, chances are your lift pump is perfectly fine.

How often does the car see full throttle? Believe it or not, it helps the engine rid itself of excessive carbon build up that otherwise wouldn't be blown out with normal putting around. If it's smoking dark black at full throttle and won't do it again after, you need to full throttle more often.


Sent from my toilet paper phone because it's a piece of shi....

Thanks for the info, I'll look into the timing tool, it does smoke black/grey on full throttle, sometimes its hard to see the color because of lighting, the smoke looks minor in the daytime, certainly doesn't "roll coal", but at night it fogs up anyone behind me at full throttle. Since I have owned it I drive about 60mi a day highway, and try to give it full throttle at least once or twice a day. Ive been getting around 25mpg. Also, does reaming the glowplug holes effect running aside from cold starts?

[babymog]

Sounds like injectors need cleaning, balancing (aka: pop testing), or rebuilding. Can also be caused by fuel leaks netween the IP and injectors as small leaks can throw timing off on one or more injectors and also imbalance the injection quantity. Does it idle perfectly smoothly?

[pilot53]

Originally Posted by babymog

Sounds like injectors need cleaning, balancing (aka: pop testing), or rebuilding. Can also be caused by fuel leaks netween the IP and injectors as small leaks can throw timing off on one or more injectors and also imbalance the injection quantity. Does it idle perfectly smoothly?

Alright, Ive checked everything for leaks including the delivery valve seals, its all as dry as can be. It idles very smoothly and quietly in my opinion.

[mannys9130]

Injectors are due for rebuilding at 100k easily. If the car was driven rarely, deposits can form and cause issues with the spray pattern. The injectors need a cleaning at best, and a rebuild at worst. People see vast improvements with their engines because at 200k+ miles the injectors are toast.


Smoke when the engine's cold is one thing, but smoke at idle with a fully warmed up engine eliminates the glow system as a culprit and leaves only a few possibilities.

[pilot53]

Originally Posted by mannys9130

Injectors are due for rebuilding at 100k easily. If the car was driven rarely, deposits can form and cause issues with the spray pattern. The injectors need a cleaning at best, and a rebuild at worst. People see vast improvements with their engines because at 200k+ miles the injectors are toast.


Smoke when the engine's cold is one thing, but smoke at idle with a fully warmed up engine eliminates the glow system as a culprit and leaves only a few possibilities.

Makes sense, When I save up some money I think i'm going to go for some monarch nozzles and balance the injectors.

[mannys9130]

What is the oil consumption over one OCI?

[pilot53]

Originally Posted by mannys9130

What is the oil consumption over one OCI?

Im not sure as I haven't had the car long enough, but I know it burned zero oil in 2000 miles. Just changed the glow plugs and reamed the carbon, didn't effect the cold start much, maybe it starts a little bit better.
The roughness at startup does seem to get worse the longer the car sits. The odd thing is it doesn't leak a single drop of fuel. Also is it likely for the injection timing to be off at such low mileage? I know the owners manual says to check it once at 30k miles, not sure why only once.

[pilot53]

I have some updates on the smoke situation. Since my last post I have rebuilt my injectors using monark nozzles, and I personally balanced them and spray tested them before install. The car idles very quietly and smoothly but the symptoms are exactly the same. Rough running and smoke for the first 15 seconds or so, only on the first start of the day. And smoke at idle, hot or cold, always. Sometimes the smoke is hard to see, but in the right lighting conditions you can see it clearly. Also when revving the engine it continues to smoke, but stops for a second when backing off of the throttle. Here is a list of what I have done or checked:

1. Chain Stretch, 0 degrees of stretch
2. ZERO blowby from the oil cap
3. New Balanced monark nozzles
4. turbo has no shaft play and compressor is oil free, did not check exhaust side
5. Hydraulic lifters have all been checked and are good/quiet
6. No oil usage within the last 2700 miles
7. Alda holds vacuum pressure
8. EGR pipe blocked off
9. I did notice some oil in the intake pipe
10. New Bosch france glowplugs
11. Four cans of diesel purge, until it ran clear, this actually seemed to help cold starts the most.
12. Prechambers look good, no oil or damage.
13. I did a quick visual check of the timing pin, and it was where it should be using a mirror, but I dont have access to the tool so its not 100%.

Not sure where to go from here or what else could be causing the smoke.

[pilot53]

Still trying to figure this out, I dont notice any smoke on the highway, just a little haze under hard acceleration, that is worst when the engine kicks down and the rpms are higher. And the grey smoke at idle, hot or cold, is still there. I recently did a compression test and checked timing with the proper tool, the timing was exactly 15 deg atdc, and the compression read a max of 400, with a low of 370, but it was most likely higher because the cheap gauge I had leaked air slightly. Also I have burned a quart of oil in 3500 miles, not sure if thats ok or not, running mobil 0w40, there are absolutely no oil leaks. All thats left is a new IP (dont think its that, engine idles smooth as butter), valve stem seals, and to check the rear of the turbo for oil. I had a few questions:

1. If the turbo was leaking oil from the exhaust (intake side is clean, no shaftplay) wouldn't that mean huge clouds of white/blue smoke, not just a gray to black haze? I would like to avoid having to disconnect the exhaust side if this is not likely to be my problem.

2. I took off the intake to change the injector nozzles and found it wet with oil even after disabling egr, not dripping, but wet, is this normal? The engine has no blowby out of the cap.

3. My understanding is that a diesel wont smoke from bad valve stem seals like a gas engine would, because there is little to no vacuum to pull oil down the valve stem, is this assumption correct? Again, I want to avoid the labor unless it is likely to fix my problem, but don't mind doing the job to fix it right.

[vwnate1]

Thanx for all the details ~ interesting thread .

Yes , Diesels do smoke from bad valve stem seals ! .

I bought the IP lock tool but cannot seem to find the thread explaining how to use it ? .

I too have an exhaust smoking problem @ idle .