ENGINE ADJUST HIGH ALTITUDE INFORMATION (NA5)

Any low altitude equipped with as gasoline engine may receive adjustments to improve performance in high altitude areas. The only exceptions are the California closed loop (Computer Command Control) system which is self compensating for altitude and the 2.8L automatic transmission engines which meets the altitude requirements without adjustment. Both of the engines are available in the 1982 "S" truck.

This bulletin is applicable to low altitude (NA5) trucks, both in use and new trucks classified as "exempt" under the current high altitude regulations. Chevrolet recommends that exempt vehicles should receive the applicable adjustments prior to customer delivery. A statement on the tune-up label will identify an "exempt" vehicle. Sample is shown on page 3.

Adjustments to high altitude (NA6) trucks which will be principally operated at low altitude will be provided in a separate bulletin.

VEHICLE EMISSION CONTROL INFORMATION UPDATE LABEL

The label should be affixed in a readily visible position in the engine compartment and where possible beside and existing Emission Control Information (Tune-Up) Label and should not be affixed to any equipment that can be easily detached from the vehicle.

Prior to installation of this label, the dealer code number and date of modification must be typed (with or without ribbon) or lettered with ballpoint pen in the space provided. The label can be ordered direct from Helm Industries as outlined in GM Standard Parts Catalog #89, P/N 14057201.

DEALERS AND CUSTOMER INFORMATION

Owners of 1982 low altitude vehicles taking up permanent residence in one of these high altitude counties, should be encouraged to have these adjustments performed when vehicles are brought in for service.

After performing these adjustments, dealers should advise customers that, IF THE VEHICLE IS RETURNED TO CONTINUOUS, LOW ALTITUDE OPERATION, THE ENGINE SHOULD BE RE-ADJUSTED TO LOW ALTITUDE SPECIFICATION PER THE CORRECT CHASSIS SERVICE MANUAL FOR IMPROVED LOW ALTITUDE. IF RE-ADJUSTED TO LOW ALTITUDE SPECIFICATIONS, THE SUPPLEMENTAL LABEL SHOULD BE REMOVED.

PROCEDURE

To be used for all the following 1982 low altitude engines used primarily at high altitudes.

Light Duty Federal Emission Packages

1.9L - All 2.8L - Manual Transmissions Only 4.1L - All

(1) Advance timing to a maximum of 4 DEG over specification if no or little detonation occurs.

(2) Reset idle speed to specs.

5.0L and 5.7L Federal

(1) Advance timing to a maximum of 4 DEG over specification if no detonation exists.

(2) Increase choke vacuum break setting from 24 DEG to 26 DEG.

(3) Adjust idle speeds to:

(a) Automatic transmission - idle speed should be adjusted from 500 to 600 in drive.

(b) Manual transmission - curb idle is now 700 RPM (was 600) solenoid speed is now 700 RPM (was 750).

5.0L and 5.7L California

(1) Advance timing to maximum of 4 DEG if no detonation exists.

(2) Set idle speed to 600 RPM.

Heavy-Duty Emission - Gasoline

(1) Advance timing a maximum of 4 DEG if no detonation exists.

(2) Set idle speed to specifications.

COUNTIES WHICH ARE DESIGNATED HIGH-ALTITUDE AREAS

ARIZONA MONTANA UTAH

Apache Navajo Beaverhead Madison Beaver Cochise Yavapai Deer Lodge Meagher Box Elder Coconino Gallatin Park Cache Jefferson Silver Bow Carbon COLORADO Judith Basin Wheatland Daggett Powell Davis Adams Kit Carson Duschesne Alamosa Lake NEBRASKA Emery Arapahoe LaPlata Garfield Archuleta Larimer Banner Kimball Grand Boulder Las Animas Cheyenne Sioux Iron Chaffee Lincoln Juab Cheyenne Mesa NEVADA Kane Clear Creek Mineral Millard Conejos Moffat CarsonCity Lyon Morgan Costilla Montezuma Douglas Mineral Piute Crowley Montrose Elko Nye Rich Custer Morgan Esmeralda Pershing Salt Lake Delta Otero Eureka Storey San Juan Denver Ouray Humboldt Washoe San Pete Dolores Park Lander White Pine Sevier Douglas Pitkin Lincoln Summit Eagle Pueblo Tooele Elbertt Rio Grande NEW MEXICO Unitah El Paso Routt Utah Fremont Saguache Bernalillo Mora Wasatch Garfield San Juan Catron Rio Arriba Wayne Gilpin San Miguel Colfax Roosevelt Weber Grand Summit Curry Sandoval Gunnison Teller DeBaca San Juan WYOMING Hinsdale Washington Grand Sans Miguel Huerfano Weld Guadalupe Santa Fe Albany Jackson Rio Blanco Harding Sierra Campbell Jefferson Hidalgo Socorro Carbon Lincoln Taos Converse IDAHO Los Alamos Torrance Fremont Luna Union Goshen Bannock Franklin McKinley Valencia Hot Springs Bear Lake Fremont Otero Johnson Bingham Jefferson Laramie Blaine Lemhi OREGON Lincoln Booneville madison Natrona Butte Minidoka Harney Lake Niobrara Camas Oneida Klamath Park Caribou Power Platte Cassia Teton TEXAS Sublette Clark Valley Sweetwater Custer Jeff Davis Hudspeth Teton Parmer Vinta Washakie Weston

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.