w108 Black Soot with water from exhaust at cold start

[Jazzenco]

Hi everybody,

Long time I observe that from my 280SE 3.5( D-jetronic m116.980) at cold start, there is a black soot mixed with water getting out from exhaust and there is a heavy exhaust gas smell.

If I'm not mistaken, as the exhaust pipes are black, car runing rich. Because when I touch pipes with finger, my finger gets black.

I try to adjust CO level from ECU to decrease/increase idle CO level, it's functioning we noticed but heavy exhaust smell, black soot and color of exhaust never gets better.

My ignition timing is currently BTDC 6 Degrees with vacuum and 35 degrees around 3000 rpm without vacuum.

I'm suspicious about MAP sensor because, this smell is always exist event on load(driving) not only at idle. Fuel consumption little bit higher.

In fact I electrically check MAP coil resistance and vacuum holding, it's in the range but not sure about aneroid cells position as I don't know how to check,

Do you think over time, MAP sensor, load and partial load settings changes?

Runing rich can decrease car performance?

Current fuel delivery is 2bar on ring line, all injectors are tested and cleaned.

Any suggestions about the reason?

Regards,

Kutluhan

[Tony H]

I think this is pretty normal for a D-Jet car-they run rich. The system gets no feedback and I suspect the engineers biased the system on the rich side to prevent a lean situation which would be more damaging than a rich situation. There are a lot of self learning aftermarket FI systems on the market now that can use your original fuel injectors. You would need to add a oxygen sensor.

[Jazzenco]

Thank you very much for reply. Do you think black carbon flakes in water at cold start is normal to see at exhaust tail. This is because of runing rich? Also, you mentioned about oxygen sensor, where can I install and connect with ECU? Pins to ECU?

Thank you

[Tony H]

I had the same black water on mine-that is the soot mixing with the water vapor in the exhaust-it would make a mess on the garage floor. You cannot add a oxygen sensor to D-jet-I was using that as an example of a modern closed loop system that receives feedback from the o2 sensor.

[Diseasel300]

The water is condensation. Once the exhaust system warms up, it should go away. At a cold-start, the engine is going to run fairly rich (even modern cars do) to allow the engine to run decently until it's warm enough to keep the fuel vaporized and run well on its own (similar function to the choke plate on a carbureted engine). Any time you have a sweaty exhaust, you can expect some carbon to come out with it, modern cars will even do that on a cool humid day.

I wouldn't worry too much about it. Keep in mind that you'll always smell gas on the exhaust of a vehicle without a catalytic converter, it's the nature of the beast. The smell is very different from a car with a cat and a lot of people freak out about it.

[Tomguy]

It's very normal. One time I cold-started my 4.5 with the garage door closed, about 14 years ago; the soot stain is still on the inside of the door!

[97 SL320]

The no black soot in tailpipe = OK was only valid on leaded fuel cars and modern ( 90's + ) feedback fuel injection cars. Lead would coat the exhaust leaving it gray, with modern FI fuel control is tight enough the tail pipe won't get black.

Water from the exhaust is a byproduct of combustion, and is one reason why it is a bad idea to start a car for 10 min on a regular basis then shut it off.

[Tony H]

If one goes to car shows you will be reminded of what car exhaust used to smell like. A lot of people in the hobby are not old enough to know that's the way cars used to smell. Where I moved to smog inspections are not required (at all) and I can smell cars with no cats.

[Jazzenco]

Thank you very much all of you for detailed information. So I understood that as the current fuels are unleaded not like in the past , exhaust will never be grey or rust color inside. As a result, car is running rich at cold start and does not have catalytic converter, until car warms up eyes burning(if I come very close to exhaust pipes) and heavy smell is normal?


By the way, there is a lead additive for patrol in markets, brand called liqui moly. Have you ever used? Or recommend to use?

Thank you very much for all again for detailed information


Kutluhan