What is the cause of the rotten egg smell my car makes when I drive it?

May 5, 2005 11:37 PM

It seems whenever I drive my 1996 Ford Contour over 40 mph or use my air conditioning, the car begins to smell of sulfur or rotten eggs. What do I need to do to fix this on my own?
posted by JFunk2800 to travel & transportation (7 answers total)

There's sulfur in fuel additives; your engine isn't burning it completely and your catalytic converter is storing it and then releasing it as hydrogen sulfide when you add load to the engine and force more air through.

Try switching gas stations, or fuel grades; then try a thorough tune-up: replace the spark plugs, plug wires, fuel and air filters, and oxygen sensor, and clean the fuel injectors. If that doesn't do it, replace your converter.
posted by nicwolff at 12:11 AM on May 6, 2005

Dealers will always blame cheap gas rather than the catalytic converter. If you do a lot of short hop driving, you may need to blow out that cat with an Italian tuneup. First, make sure your air filter is in good condition, or replace it, it's cheap. Then tank up with premium unleaded and get out on the superhighway or other open road where you can drive at sustained high speed to heat up the platinum catalyst and burn out the gunk.
posted by planetkyoto at 12:13 AM on May 6, 2005

Even if the fuel itself is OK, you may have a fuel mixture problem, if one of the sensors is bad or the computer is misconfigured. But for that you'll want a mechanic.
posted by nicwolff at 12:17 AM on May 6, 2005

Second nicwolff. Many cars make that stink when started from cold, because the converter can't convert all of the rich mixture that keeps a cold engine running smoothly. It's less noticeable with fuel-injected engines, because of the more-accurate fuel metering.

I can't guess why the AC makes this happen, and if the tuneup doesn't cure it, you're probably going to need a mechanic.
posted by Kirth Gerson at 4:17 AM on May 6, 2005

I have a 1995 Ford Contour and it used to do the same thing. Chances are, like everyone else has mentioned, it's the catalytic converter. That was the problem with mine.

It is fairly expensive to replace, however.
posted by C17H19NO3 at 6:36 AM on May 6, 2005

When I was a kid in the car and the catalytic converter kicked in, someone in the family always said: "Whew! There goes the crapalytic converter."
posted by Specklet at 10:39 AM on May 6, 2005

A/C will make this happen because the computer is enriching the mixture to account for the horsepower requirements of the A/C compressor.
posted by Mitheral at 11:33 AM on May 6, 2005