Greetings All,

I've got perhaps a dumb question, but I'm asking it anyways. What does black smoke coming out the tailpipe mean to the operator of a diesel engine at a no-load condition running flat?

If my survey answers don't fit the bill, please elaborate in a post.

Thanks,

Charles

__________________
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan

Water condesation?

__________________
... Kerry

126 tailed by a 203, 129 leading the pack.

Its getting too much fuel.. black smoke is uburnt fuel could be caused by injection timing or your ALDA out of whack among other things. Also could be caused by lack of air in the engine.. ie: clogged air filter.

Black is fuel. Blue grey is oil and White grey is water they say, although I could be wrong about the last two.

Filters are always worth changing, getting your injectors checked is also worth the effort, if the diesel has been condensated with dampness the spray nozzle thingy from the injectors opens up due to the effect of high temperature water (steam) going through them. Could be the cause of the smoke.

__________________
306D 1975 (camper) - rusting away
W116 450 SEL 1975 - sold
W114 long wheelbase ambulance, 3 litre diesel 1974

VW Golf 1 convertable - midlife crisis item
VW T4 van - support vehicle

Black smoke off idle at low load usually means low compression, unless you are driving a VW/Audi, in which case there is always a small "flag" of black smoke.

Black smoke under load has too many causes to come up with a simple diagnosis without more info!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Improper fuel mixture, for what ever reason (over fueling, dirty filter for inlet air etc.) Also low compression, and don't overlook poor quality fuel, or wrong fuel for that matter, bad injector on one or more cylinders, (overfuel), need I go on. No one answer, problem just has to be checked out.

The responses you received mostly apply to gasoline engines. The theory of a diesel engine and many of it's traits are totally dissimilar to their gasoline cousins.

Black smoke means that there is unburned fuel. The most common cause is dirty injectors, which have a spray pattern that is not uniform, causing incomplete combustion.

A tired engine, with blowby or worn guides allows oil in the combustion chamber. This will be burned as fuel to a certain point, when the engine really starts pumping oil the injectors get really crudded up causing this problem.

The second most common cause is, in the case of a turbo an incorrect ALDA adjustment or a problem with that system.

The third is a problem with the injection pump.

Blue smoke is of course an indication of so much oil in the combustion chamber that it cannot be burned and comes out the exhaust. This is more prominent in a gasoline engine because oil will be more easily combusted in a diesel engine rather than make it out the tailpipe.

From your description, it sounds like dirty injectors are the culprit, but you won't know until you start eliminating things. The first step is typically injector cleaner. I ran some through my daughters car after the engine overhaul. It's not perfect now, but it helped alot. The engine was sucking so much oil before the overhaul that the injectors were a real mess. Maybe I'll break down and replace them.

Have a great day,

Until you're certain otherwise, it's safe and cheap to assume it's dirty injectors like Larry stated.

Get some STP diesel injector cleaner (the blue bottle, not the red one, that's for gasoline), available at almost any chain parts shop. Pour it in at next fill-up, and see what happens. Run it hard for that tank to blow out any carbon & soot buildup from the valves & pistons.

Better yet, get some Diesel Purge (probably available from FastLane or PartsShop) and run it directly into the injection pump, following its instructions. This is heavy-duty stuff! If you have (that is, HAD) dirty or clogged injectors, you'll feel a significant improvement immediately.

Also, have you done a valve adjustment recently? You don't say what model you've got. The W123s and earlier require valve adjustment as routine maintenance. Again, a cheap fix that can be done in an hour by an experienced mechanic or in three hours by a first-time do-it-yourselfer.

- Nathan
'83 240D "Steiner"
'00 New Beetle TDI

Greetings All,

I guess I am grasping at simple solutions to perhaps a combination of things that contribute to a smoking diesel. When starting the diesel in the morning I notice a small trail of black smoke as I head down the road, probably because I don't let it sit and warm up much more than a minute or two before taking off. I suppose cold cylinder walls and the overall cold condition of the engine hasn't got things seated as a warm engine does. I don't get black smoke or even what I consider a trace haze after the little gal is warmed up to operating temps.
Blowby, yes I'd say there is some without a doubt. I checked the compression way back in Jan. when I got it only using a gas engine compression tester, it only went up to 300Lbs but all cylinders seemed to max it out. I know that isn't the most accurate way of doing things, but I was searching for a problem at the time and that's all I had. At the same time I pulled the injectors and they looked alright, just a trace of soot at the tips. I also looked into the intake manifold and found traces of oil residue that would confirm some useage of oil. I think I lose more oil out the rear crank seal than anywhere else. It doesn't leave a puddle or even a spot unless I park uphill and the oil is of course forced to the rear of the engine. I get a decent spot then. I don't know how much pressure is put on the seal traveling down the road at 60 or so mph but I'd say I lose about a quart between oil changes. Wish there was a fix for this leak without pulling the engine. If you have a make shift idea, let me know.
I also ran diesel purge through the system, directly into the pump back in March. No garbage came out and the return purge was as clean as what it was drawing, so I have doubts about dirty injectors. The spray pattern may be screwed up though as I don't have one to bench test them out . I do however feel that all diesel fuel is not created equal and some burns better than others. I have also used the diesel fuel additives such as Redline 85+ as well as it's brother. I don't want to feel like I spent over $6 bucks for something that didn't work, but it really did. I can't see paying that amout on an every fill up basis, diesel is costly enough without jacking up the price with additives.
All in all, I guess I was wondering if I screwed up the injection timing the last time I drip tested it. It definitely isn't an easy thing to do or else I'm doing it wrong. Constanly pumping the primer pump to keep fuel moving in the system while testing kind of throws you off as to whether it dripped or not.
Wish i had a reliable diesel shop within decent driving distance, I'd have them give it the once over, including the leakdown test to find out where compression might also be going.


Charles

__________________
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan