Rotten Egg Smell in exhaust 1

[BrianR]

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.

 

[patprimmer]

Sulphur can be a normal impurity in the fuel.

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.

 

[Chumley]

The reduction section in your catalytic converter, the part that changes NOx and some CO (carbon monoxide) back to N2 and CO2, also has the tendency to start absorbing SOx, or oxides of sulfur when its internal temperature drops below about 500°C. As Pat stated, sulfur is a natural contaminate in most fuels which, when burned, are emitted as oxides of sulphur.

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

 

[BrianR]

Chumley and Pat, those comments were very informative. Thank you.

 

[rmw]

If you are in the USA, you might have gotten ahold of some of the high sulphur unleaded gasoline distributed by two name brand refiners recently. There have been some real horror stories. It has been in the national news lately.

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

 

[BrianR]

rmw,
I am in Australia but there's no reason why they wouldn't have shared the junk.

 

[Metalguy]

Chumley,

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.

 

[Chumley]

Metalguy. Yeah, that's true. It is the catalytic converter that actually creates and stores most of the H2S and under certain conditions, releases it in quantities that you can smell. Remember that in 1975, that was the industries first shot at getting the converter technology to work. It's so much better now.

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

 

[patprimmer]

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 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.

 

[Chumley]

Pat writes:

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

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

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

 

[patprimmer]

It is from personal experience that I comment.

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.

 

[Chumley]

Patprimmer: I just found something interesting about H2S.

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

 

[JDana]

I have a 96 Grand Cherokee with a 2 yr old OEM converter with about 25,000 miles on it. It smells like sulfer lately (I asume from cheapo gas) will running better fuel eventually purge the sulfur smell? How about running hard with good fuel?