Why does my exhaust smell like rotten eggs?
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For the same reason rotten eggs smell like rotten eggs: Sulfur. (Also spelled "sulphur")
The catalytic converter
(and water in the exhaust) react with the fuel's
sulfur, causing the bad smell. The problem primarily affects cars with
very new cats, and which live in areas with high sulfur content in
their fuels. Over time, the catalytic converter will get coated from
normal use, its efficiency will be reduced and the smell will go away.
Sulfur will normally NOT
damage the engine, and will
NOT affect your ability to pass emissions tests. However, there are
rare circumstances where the problem can be severe enough to cause
damage to the catalytic converter. Since the car or cat will be under
warranty, the best thing to do then is to take it in to the dealer and
have the pros tell you everythng's OK.
gives the details of the issue.
An excerpt from that page:
Here's a Toyota
TSB saying much the same thing.
It's very expensive to
from fuels. Since all the pressure for removal comes from
government regulation, refiners are reluctant to voluntarily be the
first to undergo the necessary large expenditure until everyone else is
forced to face the same big bills. Motor fuels are fairly low-profit
commodities. Nobody wants to be the only one stuck with unique heavy
expenses in a low-margin business. Eventually, tighter sulfur
regulations will cover all of North America, and the rotten egg thing
will be gone forever (and your fuel will be just a bit more expensive!).