DIESEL ALTITUDE ADJUSTMENTS ADJ. TO IMPROVE PERFORMANCE

1983 Monte Carlo models equipped with 4.3L V6 diesel engines will be manufactured with either high or low altitude diesel emission systems. Cars equipped with the high altitude emission 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 car was built for primary use at either high or low altitude. These procedures are considered al- titude performance adjustments and apply only to in-use vehicles. They should not be used to modify vehicles prior to sale.

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 following adjustment procedure. This adjustment 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 with the assembly shown in Figure 1. Refer to parts information for part numbers.

2. Install timing meter J-33075 or equivalent, set pump timing to -6 DEG, and set engine idle to specifications, turn off engine.

3. Remove air crossover assembly. Install screen covers J-29657.

4. With transmission in park and A/C off, start engine.

5. Loosen locknut (Figure 2) and slowly turn metering valve stop screw clockwise until idle speed drops approximately 10 rpm.

6. Turn metering valve stop screw counterclockwise exactly 2 1/8 turns. Tighten locknut.

7. Check for fuel leaks around metering valve stop screw.

8. Turn engine off.

9. Remove magnetic tachometer probe and screened covers from intake manifold and reinstall parts removed.

10. Fill in dealer code and date on the supplemental emission control label, P/N 14057201 or equivalent (Figure 3). This label must be placed next to the existing underhood emission control information label. 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 22519396 or equivalent

2. Label 14057201 or equivalent

SUGGESTED TIME

The suggested time to perform the Low to High Altitude Adjustment and part replacement is 0.8 hour labor.

CONVERSION OF HIGH ALTITUDE SYSTEM TO LOW ALTITUDE

Dealers should advise owners moving to low altitude areas that they should purchase the following altitude adjustment procedure. This adjustment 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 with the assembly shown in Figure 1. Refer to parts information for part numbers.

2. Install timing meter J-33075 or equivalent, set pump timing to -6 DEG, and set engine idle to specifications, turn off engine.

3. Remove air crossover assembly. Install screen covers J-29657.

4. Loosen locknut (Figure 2) and turn metering valve stop screw counterclockwise 1.5 turns. Tighten locknut.

5. Start engine. With engine running and transmission in park, check for fuel leaks around metering valve stop screw.

6. Turn engine off.

7. Remove magnetic tachometer probe and screened covers from intake manifold and reinstall parts removed.

8. Fill in dealer code and date 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. 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 22519395 or equivalent 2. Label 14055121 or equivalent

SUGGESTED TIME

The suggested time to perform High to Low Altitude Adjustment and part replacement is 0.8 hour labor.

DESIGNATED HIGH ALTITUDE COUNTIES* Requiring Hiqh Altitude Emission Control

STATE OF ARIZONA STATE OF NEVADA Apache Carson City Humboldt Navajo Douglas Lander Elko Lyon STATE OF COLORADO Esmeralda Mineral Eureka Storey Adams Jefferson White Pine Alamosa Lake Arapahoe La Plata Archuleta 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 Miguel Crowley Mantezuma Grant Santa Fe Custer Montrose Guadalupe Sierra Dolores Morgan Harding Socorro Delta Ouray Lincoln Taos Denver Park Los Alamos Torrance Douglas Pitkin Luma 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 Migual 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 Bonneville 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 Beaverhead Madison Fremont Platte Deer Lodge Meagher Goshen Sublette Gallatin Park Hot Springs Sweetwater Jefferson Silver Bow Johnson Teton Laramie Uinta STATE Of NEBRASKA Lincoln Weston Banner Sioux Kimball

*Counties vhich have substantially all of their area above 4000 ft. Ref. Federal Register, Vol, 42, No. 769 April 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.