Noticed some black smoke stains on the driveway after operating the 1991 560SEL. I've read this might be a bad ignition coil. any ideas?

might be a bad coil, leaky injectors, leaky fuel dist., platinum plugs, worn cap and rotor, etc. only way to find out is to get a spark tester for the coil and look at the injectors, etc. for leaks. could even be everything. done that a couple of times. the tester needs to be something that plugs into a plug wire and is adjustable up to 40kv or so. you need to see 25-30kv as a test for a good coil. good luck, chuck.

OK, any particular brand of spark tester that would be best for this job?

no brand per se, here's a picture of an example-

Amazon.com: Thexton 404 Adjustable Ignition Spark Tester: Automotive

good luck, chuck.

Is it misfiring too?

How does it run once on the go?

Need more symptoms.

RayH

it runs rough for the first five seconds upon first startup of the day then smooth as glass for the rest of the day.

That's the exact opposite of problems I've had so I'm probably not your best bet.

I wonder if it might generally be running rich but if you're happy with fuel consumption I imagine that it's merely a cold issue. I'd look at the cold-start injector first but I've never had problems with cold start.

Best to wait for the brainy boys to suggest something.

Bonne chance.

RayH

ok, that smells just like leaky injectors and/or fuel dist. it STILL could be a weak coil also, as a weak coil takes longer to fire a cold motor and fuel goes unburned. you didn't mention odometer mileage, but after 150k or so, all 3 would not surprise me. along wih the cap, rotor, plugs and wires. gotta look at everything. and don't cheap out on the parts-go bosch with the cap and rotor, bosch or ngk coppers for plugs, no platinums allowed, and beru or karlyn for wires, no bosch allowed. good luck, chuck.

Thanks everyone for the input, I think with the age and mileage of the car, most likely everything mentioned needs to be replaced. All it takes is time and money.......

We get black stains on the driveway from the condensation blowing/dripping out of the exhaust pipes when it is cold here. I don't know what your weather conditions are like now, but here in the winter, when we start up our cars (and warm them up for a few minutes) there is cloud of steam that rises from the warm exhaust- as the condensation that settles in the exhaust is burned off. There is steam and dripping until it's burned away, and it leaves little black spots of the driveway, since the moisture carries carbon deposits out the tailpipe. With good plugs and wires, good cap and rotor, etc. in a gas model, it may be a similar situation. Good luck.

Car runs rich when cold and first started, produces carbon, winter, condensation, blah, blah, blah there's nothing abnormal or wrong with this car. However if you have money to burn, start spending. Quick easy fix, take the hose and attempt to flood the last section of the exhaust, while the car is running. You will flush out a good half cup of carbon residue. In a couple years when you notice the carbon again repeat method



'91 350SD 200,000
'91 350SDL 296,000
'94 SL500 66,000

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'94 SL5000 60,000
'91 350SDL 545,000
'91 350SD 197,000
'00 E55 AMG 77,000

Classic symptoms of leaky injectors. You'll need to replace them -- about $30 apiece via auto haus az dot com. Be sure to get new plastic holders and injector seals, too. Cheap parts, all, but get the seals and holders FACTORY ONLY parts - DON'T USE AFTERMARKET FOR THESE - and order them via parts dot com.

The reason for the 5 seconds rough running is that you have one or more injectors that are leaking gas into the cylinder after the car is shut off. The rough running is the engine working through the spilled fuel, and then settling down into a normal idle pattern once the excess fuel is burned off.

It's about a 2-hour DIY job to replace the injectors. DON'T try to "clean" them with Techron or other injector cleaner. They are worn on the inside, so no amount of cleaning will cure them. Just do the right thing and replace them.

Cheers,
Gerry