Rotten Egg Smell in exhaust
Rotten Egg Smell in exhaust
(OP)
I have started to notice a rotten egg smell from my car's exhaust, and suspect it might be the catalytic converter. The vehicle is a GM Vectra V6 which uses premium unleaded and has always had the correct fuel (although who knows if a fill was adulterated with something else).
My question is do you think the converter is dead, and if so will this damage the engine, apart from the pollution issue.
My question is do you think the converter is dead, and if so will this damage the engine, apart from the pollution issue.





RE: Rotten Egg Smell in exhaust
If present, it converts to H2S in the combustion process or catalytic converter, giving the smell.
This is one of the undesirable side effects of polution control and lower quality unleaded fuels
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Rotten Egg Smell in exhaust
When the engine is required to put out more power and the catalytic converter heats up over 600°C, the catalytic converter starts releasing the SOx as H2S and SO3. The SO3 has no odor but the H2S (Hydrogen Sulfide) gas does, which is what you smell. That usually means the reduction section of your converter IS working, regenerating itself, and purging the accumulated sulphur. The older your O2 sensor and catalytic converter is and the slower they react, the more H2S you'll tend to get.
Because sulfur reduces the catalytic converters efficiency in converting NOx, it's conentration in gasoline and motor oil is being reduced in the U.S. (eventually close to zero) by EPA and CARB pressures. Most standard U.S. emissions tests check for NOx emissions but don't (yet) check for SOx or H2S emissions.
Chumley
RE: Rotten Egg Smell in exhaust
RE: Rotten Egg Smell in exhaust
It even made one of the questions on Klik and Klack the tappett bros on NPR last Sat AM.
I would prefer not to say the corporate names here, but you can find out easily enough. You might be one of the unlucky ones to have encountered this.
rmw
RE: Rotten Egg Smell in exhaust
I am in Australia but there's no reason why they wouldn't have shared the junk.
RE: Rotten Egg Smell in exhaust
Apparently the early (1975, etc) cats could also trap S, because I remember how those cars stunk so bad. This never happened on a cat-free car.
RE: Rotten Egg Smell in exhaust
I bought a Honda with the CVCC engine in 1975 (no converter required) just so I wouldn't have to deal with the then new technology. The $.10 per gallon price difference ($.55 per gallon vs. $.65 per gallon) between leaded and unleaded regular, and the minimal drivability issues also had something to do with my decision which proved over time to be a good one if you don't count the brain damaged infants harmed by the additional lead my car emitted while getting 30mpg and emitting little or no H2S.
Chumley
RE: Rotten Egg Smell in exhaust
You might be wise to look up an MSDS on it.
From memory, it initially smells real bad, but as we become affected, the smell reduces, we get a sweet taste under the tongue, and become intoxicated, then unconscious.
Like alcohol, sufficient exposure to cause noticeable intoxication will, will also cause a headache as an after effect
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Rotten Egg Smell in exhaust
It should be borne in mind that H2S is also quite intoxicating and toxic.
You might be wise to look up an MSDS on it.
From memory, it initially smells real bad, but as we become affected, the smell reduces, we get a sweet taste under the tongue, and become intoxicated, then unconscious.
Like alcohol, sufficient exposure to cause noticeable intoxication will, will also cause a headache as an after effect.
Regards Pat
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Cool. It must be a delayed effect. Our qualitative/quantitative analysis chemistry lab stunk of H2S every day. (well at least for the first hour) For 3 hours a day over 12 weeks I was exposed to it. Both instructors told me I should consider a different career path. Although I was one of the highest ranking students, I listened, just may be not soon enough! Most pre med students (now doctors) had to stay there in for far longer than I did!
Chumley
RE: Rotten Egg Smell in exhaust
When studying polymer chemistry, we had legitimate need to run a process where H2S was a byproduct. The fume cupboard failed, but we braved it out for a while. We did get effected, and suffered some headache.
The first car I had that used a catalytic converter left me with the sweet taste a few times. it probably would not have been recognised except for the previous experience.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Rotten Egg Smell in exhaust
According to this:
http://www.atsdr.cdc.gov/toxprofiles/tp114-c3.pdf
H2S has an odor threshold of .5 ppb. (that's parts per billion which is very very low) In another report I found that concentrations over about 100 ppm (parts per million) H2S has a numbing effect on the human sense of smell and can produce major headaches. That is also consistent with my chemistry lab experience!
So even though you can smell H2S as it comes out of the catalytic converter/tailpipe, the quantities produced are very low and wouldn't likely show up on anything but the most sensitive test lab equipment. (the human nose being one of them in the case of H2S)
Chumley
RE: Rotten Egg Smell in exhaust