Black Smoke coming out from exhaust

[1994volvo855T]

HI,
These days, I have been having black smoke coming out from muffler.
This does not happen all the time.
When I stucked in traffic jam or stopped about 5min with engine running, and start the car, I could see black smoke in rear view mirror.
What is this black smoke? I do not have "Check Engine" light.
Also, black smoke smells some cemical burning but not burning oil smell.

Thank you

[Jensen]

Sure your engine isn't running rich (too much fuel- multiple causes)
Could also be failling catalytic converter.

[UncleBoost]

Unplug your temperature sensor and see if the problem still exists.
Easiest thing in the world to try. If the smoke goes away, replace the Water Temperature sensor just under the thermostat housing. Don't ask why it works, it did for me. I had black smoke, High sporatic Idling, hard starting, No starting...the list goes on.

Holla back if it works.

DC in North Carolina

[Yetiman]

Unplug your temperature sensor and see if the problem still exists.
Easiest thing in the world to try. If the smoke goes away, replace the Water Temperature sensor just under the thermostat housing. Don't ask why it works, it did for me. I had black smoke, High sporatic Idling, hard starting, No starting...the list goes on.

Holla back if it works.

DC in North Carolina

It works because the computer gives the engine a richer fuel mixture when the engine is cold so it starts and warms up more easily. If it never sees the coolant warm up, the rich condition continues, Your car smokes and gets poor fuel economy and you eventually start dumping raw gas into the exhaust (cat converter) which makes things even worse.

The coolant sensor is Definately the first thing to check (replace, it's like $17 from a reputable source). It's worth having a spare one in your toolbox at home for those times you need it.