I have a 04 3.5 L and the tail pipe is clean, I mean I put my finger in the tail pipe and rub it across the length of my finger and it is clean.Carissa249 said:Hi everyone, my car has been getting bad gas mileage. (see my other post). The dealership is giving me the run around. But today I was looking at the tailpipes and both of them are covered in black soot. What could this mean?
Well I must have the only car in the world with a clean tail pipe, 17 K miles. Soot is unburned fuel, a pure waste, you should check some more tail pipes before you call my statement BS. I will call the Guiness Book of records to get it in if I have the only one. BTW 35 MPG at 70 MPH, not much left for soot.bigbengt67 said:^ Cars are dirty machines, carbon is a by-product of the combustion reation that occurs in an engine. It ends up at the tail pipe, end of story. Take a walk in any parking lot and look at every cars exhaust, I promise the overwhelming majority will be black. There are only two reasons for a "clean" tail pipe.
1: The owner scrubs the hell out of them periodically.
2: The car is relatively new and has low miles such that the carbon hasn't built up yet.
Don't go telling people they have a problem until you look around a little bit.
Not to be picky, but the catalyst on a vehicle is not their to take care of unburnt fuel. In fact, unburnt fuel entering your catalyist will likely damage it if exposed long enough. Combustion in modern engines is not perfect, but a good engine comes very, very close. The actual combustion itself is very efficient. But your point is correct, the engine does produce some carbon and it will lead to a SLIGHT buildup on the exhaust, however I would say anything more than a dirty coating would be excessive. If you can wipe your finger across it and collect a gob of soot, then you might have a problem. However, the likelyhood that your having a fuel metering/combustion problem without the ECU picking up on it is probably pretty slim.bigbengt67 said:^ Soot is NOT unburned fuel, it is a by-product of the combustion process. The first law of thermodynamics says matter cannot be created or destroyed. If you are burning fuel it will be changed into another form. Carbon is what comes out of most combustion reactions. Anything you burn will produce by-products.Catalytic converters try to take care of any unburned fuel after it leaves the engine.
Here's the equation for burning fuel in a combustion reaction:
CxHy + (x + y/4)O2 ? xCO2 + (y/2)H2O
X and Y are various ratios of hydrogen and carbon that are what differentiate fuels (Propane, methane, butane, gasoline...)
In the real world things do not work out perfectly, if they did we would not have carbon monoxide and NOx emissions to worry about in our cars; only water and carbon dioxide.
In short, a real world combustion reaction WILL produce carbon atoms not bonded with any other molecules. That carbon is what turns your exhaust black.
This sounds about right. Any black you have on the tailpipe shouldn't really be something that wipes off easy. If there is so much that you can collect powder on your finger, then you would probably want to look into it.Lucius said:Black on mine. I tried wiping it off with a dry paper towel once to see if it would do anything, but it didn't.
Too lazy to clean them.
If the ECU never makes it into closed loop mode with O2 sensor feedback (for what ever reason), it will never be able to recognize that it is running too rich or too lean. This is always one of the first step in diagnosis - verifying closed loop mode with no codes set.jp375 said:However, the likelyhood that your having a fuel metering/combustion problem without the ECU picking up on it is probably pretty slim.