black smoke constantly - PeachParts Mercedes-Benz Forum

300SD81 · #1 08-23-2008, 04:35 PM

My car seems to have started to put out black smoke constantly. The first thing I thought was head gasket (between cylinders, since oil/coolant are both fine) since I overheated it a while back, and bought a compression tester, it has 400-420psi compression on all cylinders. I don't see how it could possibly be over fueling, since it does it at idle, and theres definitely more then enough air at idle.. Any ideas?

300SD81 · #2 08-24-2008, 12:33 AM

I'm only home from college for this weekend, so I really need to get this fixed.

Things I've tried so far:
Compression Test - 400-420psi on all
Oil Change - needed one anyway, no effect
Checked Valves - adjusted a month or so ago, still good
Diesel Kleen - not sure yet, poured in whole bottle, about 20x recommended concentration, can't get diesel purge locally.

What could cause black smoke, which I assume is unburnt fuel, at idle? It smokes throughout the range as well, power seems ok, maybe a little less than before but that could just be in my head.. The smoke seems white at times too, but isn't that partially burnt fuel?? My oil was completely water-free, and I'm not experiencing any coolant loss or oil in coolant either, so with the high compression numbers, I doubt its the headgasket, which I suspected since she was overheated a while ago.

compress ignite · #3 08-24-2008, 01:45 AM

That I.P. will fuel the engine mercilessly with no idea the Air Filter is clogged.

bgkast · #4 08-24-2008, 01:58 AM

Have you tried an Italian tune up?

If so take the injectors to a shop to have them checked for spray pattern.

Mister Byrnzoil · #5 08-24-2008, 07:41 AM

too much fuel (or bad spray pattern) or not enough air.

take her for a quick spin w/out the air filter, any change?

I would recommend finding some diesel purge and starting there.

Brian Carlton · #6 08-24-2008, 10:00 AM

Quote:

Originally Posted by 300SD81

What could cause black smoke, which I assume is unburnt fuel, at idle? .

Since you have good compression, the possibilites are limited to an injector or the IP.......with the injector being the most likely culprit.

See if you can isolate the cylinder by cracking each injector nut........in sequence.......in an attempt to see when the smoke disappears. The engine will run a bit rough on four........but, that's not a problem. You're looking for the one injector that will stop the smoking at idle.

When you find it, either remove it and take it to an injector shop...........or swap it with another cylinder and perform the same test again and see if the problem goes with the injector. This would provide positive confirmation of the injector as the problem.

BTW, I'm making the assumption that you've already checked the basic points regarding airflow........dirty air cleaner......debris in the intake.........plugged intake snorkel..........the most basic maintenance tasks that anyone who owns these vehicles should do before posting a question on here.

300SD81 · #7 08-24-2008, 10:43 AM

I've already checked the air filter, intake, etc, the one in there is less than 3 weeks old as well, and still looks new. I'm guessing I have to buy some heat shields before I do anything involving removing the injectors? How much should I expect to pay to have them tested?

winmutt · #8 08-24-2008, 12:02 PM

Turbodiesel electric (the Bosch shop in collega park) quoted 20 per with cleaning and shimming. start with cracking the injectors one at a time until you find the culprit.

Diesel911 · #9 08-24-2008, 12:35 PM

Did the problem start after the car was over heated?

300SD81 · #10 08-24-2008, 01:05 PM

I first noticed it about a month after the overheating, can't tell if its related or not. There seems to be less smoke now, could removing/reinserting the glow plugs have done anything to effect smoke? Or maybe the diesel kleen is doing its job...

DieselClack · #11 08-24-2008, 02:08 PM

I would suspect the fuel injectors since black smoke is an overly rich fuel condition!

It sounds like it's injector overhaul time.

Thecorrupterx · #12 08-24-2008, 02:27 PM

is the ALDA in good shape?

dieselnutnj · #13 08-24-2008, 09:14 PM

look for any restrictions in the air intake system as well. I didnt read everything, but does your car have any loss of power at highway speed? I doubt the overheat hurt anything since your compression is very good. You mentioned you put diesel clean in it? Less smoke now? I'd lean towards dirty or sticky injectors.

pawoSD · #14 08-24-2008, 10:05 PM

Quote:

Originally Posted by Mister Byrnzoil

too much fuel (or bad spray pattern) or not enough air.

take her for a quick spin w/out the air filter, any change?

I would recommend finding some diesel purge and starting there.

By all means do NOT do that! Never ever run the engine without the air filter, especially while driving, imagine what happens if a small pebble or something flew into the intake! Boom smash bang, silence. It'd ruin the turbo and probably some of the engine on its way through.

Always use an air filter!!

Caduceus · #15 08-25-2008, 01:59 AM

Quote:

Originally Posted by pawoSD

By all means do NOT do that! Never ever run the engine without the air filter, especially while driving, imagine what happens if a small pebble or something flew into the intake! Boom smash bang, silence. It'd ruin the turbo and probably some of the engine on its way through.

Always use an air filter!!

Pshhh,

I don't think anything TOO harmful could make it through the overkill of a metal screen inside the air cleaner. If the purpose it just to test it for a FEW minutes....