anyone had a sulfer smell from the exhaust? What could that mean? Car is running fine, I did get a code once about fuel trim too lean but its not done it again since codes were cleared out.

 

It just seems to happen, usually after driving quite hard.
It is almost certainly due to the Devil in the CAT but he won't tell us how he does it.

 

I've seen cars in perfect condition that produce the odor intermittently. If the fuel trims read normal and you in fact have no misfires, it's probably nothing to worry about.

Below is something I found that seems to make sense. I'm not smart enough to write this.


"It's (the smell) hydrogen sulfide or H2S. It does not exist in the fuel or oil, which is why you can't smell it at the gas station. It does, however, come from the gasoline. Almost all gasoline contains organic sulfur compounds with sulfur levels ranging from 30 to 100 parts per million, approximately.

"As the fuel burns, the organic sulfur compounds break down into simpler compounds. If the engine is running lean (more air than is needed to burn the fuel), the sulfur is likely to be SO2, or sulfur dioxide. The catalytic converter can change this into SO3 (sulfur trioxide), which then reacts with the catalyst to form sulfates on the catalyst. Over several minutes there is a build up of sulfates. If the engine suddenly starts to run rich (not enough air to burn all the fuel), such as when you stop at a red light, climb a steep hill, or brake hard to slow down, the chemistry changes. Now the sulfates are unstable and they react to form hydrogen sulfide, which is expelled from the exhaust pipe all at once. The high concentration is the reason for the bad smell! This effect is a common problem with new vehicles because the catalyst is working at a very high efficiency. However, as the catalyst gets older, the activity drops. Fortunately for us, one of the first reactions to be affected is the formation of hydrogen sulfide. So as the catalyst gets older, the smell will go away. It should also be noted that many catalysts never smell bad. One reason might be because the vehicle doesn't run lean for much of the time, or perhaps the catalyst has an extra component that reduces the production of hydrogen sulfide.
"Next time Eggbert and Shelley stop behind a vehicle that smells bad, they can be grateful that it's at least not contributing much to atmospheric pollution."
Thanks to this month's Whizard, Dr. Gordon Bartley, a senior research scientist in the Emissions Research Department of the Automotive Products and Emissions Research Division. Bartley specializes in the development, aging, and evaluation of vehicle emission catalysts.