Piston Slap: Sulphur Farts

TTAC Commentator dastanley writes:

Well here I am again on Piston Slap about my 2006 Corolla w/ about 44k miles. This isn’t a burning question (no pun intended), I’m just curious. This time it’s the exhaust – it stinks. I know that the rotten egg smell comes from the catalytic converter, but why? Is the engine running rich and overloading the converter?

The check engine light isn’t on and the gas mileage is about the same, so the computer (apparently) hasn’t detected a problem. I use regular 86 octane fuel (high altitude), mostly Conoco-Phillips with “Pro-Clean”. I’ve been told that the fuel in this region of NM has a high sulfur content, although I can’t confirm that.

The exhaust odor doesn’t bother me when driving around (I’m not following my own car), but every time I pull into the garage, it smells pretty obnoxious and my wife thinks I’ve farted. WTF?

Sajeev Answers:

How the heck can you stay married when you do sulphur farts in front of your wife? It’s time to lay off the eggs and give up on the cabbage soup diet. Oh wait, you rang about the smell in the garage, not in the bedroom.

What’s happening to your Corolla is not rare. I’ve seen this many times during my 10-year quest to learn more about cars via message boards. The same two fail points always come up: Oxygen Sensors or catalytic convertors. In my experience, replacing the O2 sensors alone will clear up your farts. This is because they are gummed up with the same sulphur deposits in your catalytic convertors. But while the convertors can’t do much, the O2 sensor adjusts the air/fuel mixture, effectively toning down the amount of fuel/sulphur in your system.

Plus, replacing a catalytic convertor is a bit more than the $100-ish needed for a couple of sensors on a Corolla. New sensors, a healthy number of high throttle, high load runs down the highway (in 2nd and 3rd gear) and your problem should disappear like a ninja fart in a movie theater. If not, do one more thing before changing the cats: seafoam the motor for maximum diuretic bang for the buck.

And for the Seafoam newbies out there, keep this in mind: as with any good marriage, make sure you Seafoam your “system” away from those you care about.

Send your queries to mehta@ttac.com. Spare no details and ask for a speedy resolution if you’re in a hurry.