Exhaust - Sulfur Odor at Idle

NUMBER: 86-B-115

GROUP: 6E - Emission Controls

DATE: August, 1986

SUBJECT: EXHAUST ODOR COMPLAINTS

MODELS: 1986 M VAN WITH THE 4.3L TBI ENGINE (VIN CODE Z) AND AUTOMATIC TRANSMISSION FEDERAL AND CALIFORNIA EMISSIONS

Some 1986 M vans equipped with the 4.3L V6 engine may experience a "Sulfur Odor" at an idle after the engine has reached normal operating temperature. Sulfur odors can be an indication of a "rich" fuel mixture in the engine. This condition may be caused by an incorrect PROM calibration in the electronic control module (ECM).

If this condition is encountered and the vehicle has been checked using procedures on Page 6E2B-7 of the Service Manual, new service PROMS have been released to correct the condition. The new PROMS went into production starting with VIN breakpoints:

GB524481 - Federal Emissions
GB524599 - California Emissions

Service procedures for PROM replacement are in Section 6E2-C1 of the 1986 Service Manual.

Parts Information

P/N Emissions Transmission Axle Ratio

16068877 Federal Automatic All
16068926 California Automatic All

Notice: This prom will also reduce cold engine fast idle speeds from approximately 850 RPM to 750 RPM in drive.

Slight odor may still be present during warm-up, severe throttle maneuvers, or after wide open throttle applications. This is characteristic of systems equipped with three way catalytic converters. The vehicle should also be inspected to ensure no intake manifold or exhaust manifold leaks are present.

This bulletin applies to vehicles equipped with automatic transmissions only. When PROMS for vehicles equipped with manual transmissions are available, this bulletin will be updated.