Emissions - Rotten Egg Smell From Exhaust

Group 18
Exhaust System

Bulletin Number
18 01 93 (3846)

Woodcliff Lake, NJ
August 1993
Product Engineering

SUBJECT:
Hydrogen Sulfide Odor from the Exhaust System

MODELS:
All

Complaint:
Rotten Egg Smell from Exhaust

Situation:
Since the introduction of the 3-way catalytic converter in 1978, BMW has been working with catalyst manufacturers to find the ideal type of promoter to minimize the formation of Hydrogen Sulfide (H2S) which is a by-product of the catalytic action and is often described as a "rotten egg" smell from the exhaust. Over the years changes have been phased into production to optimize the overall performance of catalytic converters.

Sulfur dioxide (S02) is formed in the catalytic converter, which subsequently attaches to the so-called promoters during constant speed driving with an ideal air/fuel ratio or slightly lean condition. Under acceleration or slightly rich condition, S02 is reduced to H2S and released through the tail pipe. The amount of H2S that is released from the catalytic converter depends heavily on the sulfur content of the fuel being used. The higher the sulfur content in the fuel the greater the odor from the exhaust pipe under the above circumstances.

Correction:
If a complaint is received of "rotten egg" smell from the exhaust system, and there are no faults stored in the DME Engine Control Module, the recommendation of a different name brand fuel may eliminate the complaint since the sulfur content of today's fuels varies significantly.

The replacement of a catalytic converter for the above complaint should not be considered since a new catalytic converter may even emit a slightly higher amount of H2S during its initial break-in period.

Warranty Information:
Replacement of catalytic converters for the complaint of "rotten egg" smell/odors from exhaust is not covered under warranty.