Exhaust System - Sulfur/Rotten Egg Smell
Information IB03-03-S001Sulfur (Rotten Egg) Smell From The Exhaust
ISSUE DATE: APRIL 2003
Affected Vehicles
1996 to current model year Isuzu Vehicles.
Service Information
On some vehicles the customer might complain of a sulfur odor or rotten egg smell from the exhaust when coming to a stop, hard acceleration or on start-ups. The sulfur odor is neither an indication of an engine concern nor cause of reduced driveability or durability of the engine and any of its emission components. The sulfur odor is a normal by-product of the catalytic converter during normal vehicle operations.
The sulfur odor or rotten egg smell is caused by the high amounts of sulfur in the gasoline the customer is using in the vehicle. Sulfur content in gasoline can vary from 30 to 1000 parts per million, depending on the source of the crude oil, refining process, and regional regulations. The vehicle's catalytic converter is designed to break down the sulfur in gasoline into Sulfur Trioxide (S03). As the vehicle is running slightly lean for a period of time (deceleration), Sulfur Dioxide (S02) is formed in the catalytic converter. The catalytic converter chemically changes Sulfur Dioxide (S02) into Sulfur Trioxide (S03). When the vehicle engine is running in a rich condition (acceleration), the chemistry in the catalytic converter changes. The sulfates are now unstable and they react to form Hydrogen Sulfide (H25), which is expelled from the exhaust pipe in the form of an odor. The complaint is more common on newer vehicles due to the catalytic converter working at its highest efficiency. As the vehicle (catalyst) gets older the chemical activity drops and the odor does not occur as often.
Recommendations
NOTE:
Replacing the catalytic converter will not eliminate the sulfur odor. Replacing the catalyst may extend the odor presence by not allowing the converter to "age".
1. Suggest the customer try a different brand of fuel; use the new fuel for at least 100 miles.
2. Inform the customer that conditions such as extended idling, hard braking, aggressive acceleration and long "wide open throttle" maneuvers may intensify odor condition.
3. "Fuel additives" or "octane boosters" could increase the odor.
4. Request information from your local fuel dealers regarding the amount of sulfur in their fuel. Try using fuels with the lowest amounts of sulfur content.
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