Catalytic Converter - Odor At Exhaust Pipe

9229audi01

Group: 24

Number: 92-04

Date: 03/10/92


Subject:
Odor at Exhaust Pipe


Model(s):
All

M.Y. All


Condition

Under certain operating conditions, a "rotten egg" odor may emanate from the tail pipe.


Cause

^ Sulfur content of gasoline

^ The characteristic of catalytic converters to store sulfur compounds (S03) and release them during rich engine running conditions i.e., idle or heavy acceleration

Under relatively lean engine running conditions sulfur found in gasoline is converted during the combustion process into sulfur trioxide (S03).

Under relatively rich engine running conditions (idling or heavy acceleration) sulfur trioxide is converted into hydrogen sulfide (H2S) within the catalytic converter. Hydrogen sulfide has the characteristic rotten-egg odor.


Service

Recommend to the customer to try a different brand of gasoline (which may have less sulfur content).

^ Generally premium grade fuels have less sulfur content than regular unleaded fuels.

^ It may take several tanks of a different brand before a change might be detected.

^ The "rotten-egg" odor will tend to lessen as the catalyic converter ages. Hydrogen sulfide odor is usually less noticeable on vehicles with more than 6 thousand miles.

It should also be noted that sulfur content of gasoline can vary from one geographic area to another.