DIESEL ALTITUDE ADJUSTMENT ADJ. TO IMPROVE PERFORMANCE

The 1983 Chevrolets equipped with 5.7L V8 diesel engines will be manufactured with either high or low altitude diesel systems. A vehicle with a high altitude system will be invoiced with option NA6. The type of system can also be identified by the emission label attached to the fan shroud. The label will indicate that the vehicle was designed for principal use at either high or low altitude.

These adjustments are considered Altitude Performance Adjustments and apply only to in-use vehicles. They should not be used to modify vehicles prior to sale.

Dealers must not sell vehicles with low altitude systems for principal use at high altitude.

CONVERSION OF LOW ALTITUDE SYSTEM TO HIGH ALTITUDE

Dealers in high altitude areas should encourage owners who have moved to high altitude counties to purchase the service adjustment procedure outlined below, which is considered an owner maintenance expense. See attachment for a list of counties which the Environmental Protection Agency has designated as high altitude counties. Diesel timing should be checked or adjusted at the same approximate altitude at which the vehicle will be driven.

1. Replace the EGR vacuum control valve assembly (Figure 1) with the assembly shown in the parts information.

2. Install timing meter J-33075 or equivalent, set pump timing -4 DEG, and set idle speed to specifications.

3. Remove air cleaner and air crossover assemblies and install screen covers J-26996-2.

4. Install shop towel in the intake manifold valley area under the injection pump head to absorb any fuel leakage. Remove housing pressure tap plug and seal located on the rear of the pump (Figure 2).

5. Using the parts contained in kit, P/N 22516487 or equivalent, assemble locknut and new seal ("O" ring) to metering valve stop screw.

6. Install assembly in injection pump until locknut contacts pump housing. Tighten locknut.

7. Place transmission in park, turn A/C off and start engine.

8. Loosen locknut and slowly turn metering valve stop screw clockwise until idle speed drops approximately 10 rpm.

9. Turn metering valve stop screw counterclockwise 2 1/2 turns and tighten locknut.

10. Check installation for fuel leaks and remove shop towel from intake valley.

11. Turn engine off.

12. Remove timing meter and screened covers from intake manifold and reinstall parts removed.

13. Type or print with ballpoint pen the dealer code and date in the space provided on the supplemental emission control label, P/N 14057201 or equivalent, Figure 3 (part of kit). The label must be placed next to the existing underhood emission control information label to the extent possible. The label should not be affixed to any equipment that can be easily detached from the vehicle. Wash off the area with soap and water, dry thoroughly, and apply the new label.

PARTS INFORMATION Part P/N

1. EGR Vacuum Control Valve Assembly High Altitude Application - All Models 22515542 or equivalent

2. Kit Contents 22516487 or equivalent Part Quantity Locknut 1 Seal 1 Metering Valve Screw 1 Label, P/N 14057201 or equivalent 1 (See Figure 3)

SUGGESTED TIME

The suggested time to perform High Altitude adjustment and part replacement procedure listed above is 0.4 hour labor.

CONVERSION OF HIGH ALTITUDE VEHICLES TO LOW ALTITUDE

Dealers should advise owners moving to low altitude areas that they should purchase the service adjustment procedure outlined below which is considered an owner maintenance expense. Diesel timing should be checked or adjusted at the same approximate altitude at which the vehicle will be driven.

1. Replace the EGR vacuum control valve assembly (Figure 1) with the assembly shown in the parts information.

2. Install timing meter J-33075 or equivalent, set pump timing -4 DEG, and set idle speed to specifications.

3. Remove timing meter.

4. Type or print with ballpoint pen the dealer code and date in the space provided on the supplemental emission control label, P/N 14055121 or equivalent (Figure 4). The label must be placed next to the existing underhood emission control information label to the extent possible. The label should not be affixed to any equipment that can be easily detached from the vehicle. Wash off the area with soap and water, dry thoroughly, and apply the new label.

PARTS INFORMATION

Part P/N

1. EGR Vacuum Control Valve Assembly Low Altitude Application - All Models 22514746 or equivalent

2. Label 14055121 or equivalent (See Figure 4)

SUGGESTED TIME

The suggested time to perform the Low Altitude adjustment and part replacement procedure listed above is 0.4 hour labor.

DESIGNATED HIGH ALTITUDE COUNTIES* Requiring High Altitude Emission Control

STATE OF ARIZONA STATE OF NEVADA Apache Carson City Humboldt Navajo Douglas Lander Elko Lyon STATE OF COLORADO Esmeralds Mineral Adams Jefferson Eureka Storey Alamosa Lake White Pine Arapahoe La Plata Archulets Larimer STATE OF NEW MEXICO Boulder Las Animas Bernalillo Mora Chaffee Lincoln Catron Rio Arriba Clear Creek Mesa Colfax Sandoval Conejos Mineral Curry San Juan Costilla Moffat De Baca San Migual Crowley Montezuma Grant Santa Fe Custer Montrose Guadalupe Sierra Dolores Morgan Harding Socorro Delta Ouray Lincoln Taos Denver Park Los Alamos Torrance Douglas Pitkln Luna Union Eagle Pueblo McKinley Valencia Elbert Rio Blanco El Paso Rio Grande Fremont Routt STATE OF OREGON Garfield Saguache Gilpin San Juan Lake Grand San Miguel Gunnison Summit STATE OF UTAH Hinsdale Teller Beaver Plute Huerfano Washington Box Elder Rich Jackson Weld Cache Salt Lake Carbon San Juan Daggett Sanpete STATE OF IDAHO Davis Sevier Duchesne Summit Bannock Custer Emery Tooele Bear Lake Franklin Grand Uintah Bingham Fremont Iron Utah Blaine Jefferson Juab Wasatch Bonnevllle Madison Kane Wayne Butte Minidoka Millard Weber Camas Oneida Morgan Caribou Power Cassia Teton STATE OF WYOMING Clark Valley Albany Natrona Carbon Niobrara STATE OF MONTANA Converse Park Beavehead Madison Fremont Platte Deer Lodge Meagher Goshen Sublette Gallatin Park Hot Springs Sweetwater Jefferson Silver bow Johnson Tenton Laramie Uinta STATE OF NEBRASKA Lincoln Weston Banner Sioux Kimball

*Counties which have substantially all of their area above 4000 ft, Ref. Federal Register, Vol. 42, No. 76, Aprll 20, 1977, pg. 20464

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.